Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02828028 2013-09-20
I
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DRYING OF FOODSTUFFS
Field
This application relates to apparatuses, methods and installations for drying
foodstuffs, for example fruits and vegetables, especially grapes.
Background
Drying of foodstuffs is primarily done in an effort to preserve food for
future use, or to
convert one foodstuff into another. Many different methods and apparatuses
have been
developed to dry food, but one problem with drying food is preserving a
desired food quality
in the final product. Other than nutritional value, the quality most desired
to be preserved is
usually taste.
In the wine industry, berries may be first dried to reduce their moisture
content. A
berry is a fleshy fruit produced from a single ovary. Grapes are an example.
The drying
process concentrates and develops aromatic compounds, sugars and polyphenols
in the
berries. When the berries are sufficiently dry, they are further processed
into wine.
Withering of berries can be achieved by over-ripening of the berries in the
field either
on or off the vines, or indoors under fully or partially controlled condition.
Clusters of berries
are typically placed on trays in a single layer. The structure and openings of
the trays are
important factors in facilitating air movement through and around the berry
clusters, and also
play an important role in preventing the growth of undesirable mold. The
drying process can
last up to 120 days and berries are usually crushed when they have lost 30% to
40% of their
original weight.
Appassimento drying is a particular process developed in Italy, which occurs
in
dedicated lofts called fruttaio under specific environmental conditions and
through an
established method. In Appassimento wine production there are two lines of
thought: the
traditional method where natural drying conditions are an essential
requirement; or new
system designs by which postharvest stresses must be controlled and recorded.
The main
environmental conditions which are considered during drying are the
temperature and the
relative humidity (RH), which affect respiration rate. Airflow may also play a
role. Certainly, in
the traditional method, the day/night environmental variations are considered
fundamental,
as well as the specific containers used to hold the berries.
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Traditional Italian wines made using the Appassimento method, such as Amarone,
Recioto and Ripasso, command premium prices. However, wine makers in North
American
regions, for example Ontario, have difficulty creating wines using the
Appassimento drying
method due to inconsistent results, losses from mold and the labor intensive
nature of the
traditional Appassimento drying method. In order to take advantage of the
market niche for
wines made using the Appassimento drying method, it would be desirable to have
a method
by which berries may be dried to achieve the same or similar result as the
traditional
Appassimento method.
Summary
There is provided an apparatus for drying foodstuffs, comprising: a pallet
having
sides, a bottom and a top, the top of the pallet configured to support a stack
of containers
from a bottom of the stack, the pallet comprising elongated support members
forming a
perimeter on which the stack is sealingly supportable, the top of the pallet
comprising at least
one aperture to permit air flow therethrough, the top, bottom and sides of the
pallet defining a
ventilation duct for receiving air through the top of the pallet; and, a low
pressure plenum in
fluid communication and sealingly engaged with the ventilation duct, the low
pressure
plenum configured to draw air down vertically through the top of the pallet
and out of the
ventilation duct into the plenum.
There is further provided an installation for drying foodstuffs, comprising: a
climate
controlled room; and, an apparatus as defined above situated in the climate
controlled room.
There is further provided a method of processing foodstuffs, comprising
providing
foodstuffs in a plurality of containers in the apparatus in the installation
as defined above,
controlling temperature, relative humidity or both temperature and relative
humidity of air in
the room, and drawing the air in the room vertically down past the foodstuffs
until the
foodstuffs are processed.
The apparatus comprises a pallet on which a stack of containers may be
supported.
The pallet comprises elongated support members forming a perimeter. The
perimeter may
be square or rectangular in shape, although other shapes such as triangular
circular or
ellipsoidal may be used. The pallet may be conveniently sized to be moveable
by a standard
fork lift. Each elongated support member may define a side, top or bottom of
the pallet, and
other elongated support members may be employed in different locations to
provide extra
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support for the stack of containers. For example, one or more elongated
support members
may be employed as cross-members that do not define the perimeter but are
positioned to
further support the stack of containers, for example at an interface between
at least two of
the containers in a bottommost row of the stack. There should be a sufficient
number of
elongated support members to adequately support the stack of containers and to
adequately
define the ventilation duct. The ventilation duct comprises a volume defined
by the sides, top
and bottom of the pallet. The top of the pallet comprises at least one
aperture to permit air
flow therethrough.
The low pressure plenum is in fluid communication and sealingly engaged with
the
ventilation duct. The seal may be provided in any suitable manner, for example
by a gasket,
an adhesive or simply a tight tolerance between a surface of the pallet and a
surface of the
plenum. A gasket (one or more) is preferred to both reduce manufacturing costs
and to
maintain modularity of the apparatus. Gaskets may comprise any suitable
material that can
form an air seal between the pallet and the surface of the plenum, for example
foam, rubber
and the like. Preferably, the low pressure plenum is in fluid communication
with one of the
sides or the bottom of the ventilation duct. When the plenum is in fluid
communication with
one of the sides, the bottom and the other sides are closed. The sides may be
closed with
elongated support members or a blocking member, although when a row of
apparatuses are
used in an installation, only the pallet at the end of the row needs to have
all three remaining
sides closed as the pallets in the middle of the row would be in fluid
communication with the
pallets on either side. The bottom of the pallet may be closed with a blocking
member, but is
more conveniently closed by a surface on which the pallet is resting, e.g. the
floor of an
installation. The interface between the bottom of the pallet and the surface
on which the
pallet rests may also be sealed if desired, for example with a gasket or a
sufficiently tight
tolerance between the elongated support members and the surface on which the
pallet rests.
Sealing the interface between the bottom of the pallet and the surface on
which the pallet
rests is not as important because the low pressure plenum is not usually
unduly affected by
such a lack of seal unless there is a large gap.
The low pressure plenum may comprise a confined space in fluid communication
with
the ventilation duct. Any suitable air flow device may be used to create low
pressure in the
plenum, for example air pumps or fans. A low pressure, i.e. a partial vacuum,
may be formed
in the low pressure plenum by drawing air out of the plenum with the air flow
device. A fan
equipped with a variable speed motor is particularly preferred. The moving air
creates a
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pressure drop between the ventilation duct and the plenum, which draws air out
of the
ventilation duct into the plenum. The apparatus preferably comprise only one
low pressure
plenum.
A vertical stack of foodstuff holding containers may be supported on the
pallet. The
stack of containers has sides, a bottom and a top, the sides of the stack
being sealed against
air flow while the top and bottom of the stack are open to air flow. The sides
of the stack may
be sealed by using containers that have a solid surface on one side and
ensuring that these
solid-sides of these solid-sided containers are exterior facing. The sides of
the stack could
also be sealed by a sealing panel sealingly engaged with the sides, or even by
a wall of the
installation sealingly engaged with the sides. The sides of the stack could
also be sealed by
wrapping the stack in thin plastic sealing wrap. Any suitable means may be
used to seal the
sides of the stack so that vertical airflow is maintained in the stack. Thus,
the low pressure
plenum draws air vertically down through the top of the stack through the
containers through
the bottom of the stack into the ventilation duct and out of the ventilation
duct into the
plenum.
The stack may comprise one or more rows of containers and there may be one or
more containers per row. The stack may simply rest on the pallet or may be
sealingly
supported on the pallet to prevent air from leaking out at an interface
between the stack and
the pallet. Sealing may be accomplished in a similar manner as described above
for the
plenum and ventilation duct. The bottommost row of containers in the stack may
be sealingly
supported on the pallet. Each row in the stack may have substantially the same
arrangement
and perimeter as neighboring rows in the stack. The arrangement and perimeter
of the rows
may be configured to conform to the perimeter of the pallet. The containers in
a row may be
arranged so that a side of each container abuts a side of another container in
the row.
Preferably, there are no large gaps between the containers in a row. Thus, the
vertical stack
may comprise a plurality of stacked rows of containers, each row of containers
comprising a
plurality of containers arranged so that a side of each container abuts a side
of another
container in the row, each row configured to have a substantially the same
arrangement and
perimeter as a neighboring row in the stack, whereby a bottommost row is
sealingly
supported on the perimeter of the pallet.
The construction of the container may be important to provide uniform drying
of the
foodstuffs in the container. The containers, for example baskets, boxes,
buckets, etc.,
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comprise apertures in bottoms thereof configured to permit air flow at least
from above the
containers through the bottom of the containers. The containers may also
comprise sides
and the sides of the containers may also comprise apertures. The tops of the
containers are
preferably open, or at least comprise a large aperture in relation to an area
of the top.
Container size may also play a role in efficient drying of foodstuffs.
Containers having a
bottom area in a range of from about 60,000 mm2 to about 1,200,000 mm2 or
about 60,000
mm2 to about 540,000 mm2 (e.g. about 300-1200 mm or about 300-900 mm in length
and
about 200-1000 mm or about 200-600 mm in width) are generally suitable. Bottom
areas in a
range of about 150,000 mm2 to about 350,000 mnre (e.g. about 500-700 mm in
length and
about 300-500 mm in width) may be preferred in some instances. The depth of
the
containers may be conveniently about 50-400 mm or about 50-200 mm, for example
about
100-140 mm. The containers may be disposable or reusable, although reusable
containers
help reduce cost and have less environmental impact. The containers may be
constructed of
any suitable material, for example plastic, metal (e.g. stainless steel) or
wood. Plastic
containers are preferred as they are lighter, more easily sanitized and are
less likely to impart
foreign tastes to the foodstuffs.
There may be any number of rows of containers, but the most efficient number
of
rows of containers may depend to some extent on the depth of the containers,
to some
extent on the air-drawing capacity of the plenum and to some extent on the
physical
requirements of the installation in which the apparatus is used. It is
desirable for a height of
the stack to be short enough to provide easy access even to a topmost row of
containers and
to permit a uniform distribution of vertical air flow from the top of the
stack to the bottom of
the stack providing consistent conditions of temperature, relative humidity
and air flow at all
locations in the stack. The height of the stack and the air flow rate through
the stack should
be balanced to provide uniform drying throughout the stack. Given the
container depth
ranges described above, there are preferably about 5-25 rows, or about 10-20
rows, for
example 15 rows, in the stack.
There may be one or more containers in a row, but the most efficient number of
rows
of containers may depend to some extent on the bottom area of the containers,
the size of
the pallet and the desired arrangement of containers in the row. For the
container
dimensions described above, each row may contain from 1 to 8 containers or 2
to 8
containers, preferably 4 to 6 containers, for example 5 containers.
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Drawing air vertically through the stack of containers from the top to the
bottom is an
important feature. To efficiently and uniformly dry the foodstuffs in the
containers in the stack,
a uniform distribution of air flow past the foodstuffs is desired. Drawing air
as opposed to
pushing air reduces or eliminated dynamic pressure differences in the stack.
Pushing air
through the stack causes dynamic pressure wherever the air flows resulting in
uneven drying
of the food stuffs. Drawing air through the stack results in more uniform
drying.
The installation for drying foodstuffs comprises a climate controlled room and
an
apparatus as described above situated in the climate controlled room. The room
may be a
room in a larger building, or may be a building unto itself. Climate in the
room may comprise
one or more of temperature and/or relative humidity. Temperature control may
be
accomplished in any suitable manner, for example with the use of one or more
air
conditioners, heaters, and the like. Combinations of temperature control
devices may be
used. Thermostats or other automatic temperature regulation devices may be
used to
automatically control the temperature in the room to within a predetermined
tolerance.
Relative humidity in the room may be controlled with any suitable device, for
example, air
conditioners, dehumidifiers and the like. Combinations of humidity control
devices may be
used. Humidistats or other automatic humidity regulation devices may be used
to
automatically control the humidity in the room to within a predetermined
tolerance.
Temperature and humidity measurement and control devices may be in
communication with
an electronic control system, for example a computerized system, to collect
climate
information and to adjust the climate control devices as needed to maintain a
desired climate
in the room.
Although the installation may comprise only one apparatus, it is preferable
for the
installation to comprise a plurality of apparatuses. Each apparatus may
comprise a dedicated
low pressure plenum. Alternatively, one low pressure plenum may be provided
for two or
more of the apparatuses, such an arrangement reducing overall installation and
operation
costs. In an embodiment, one low pressure plenum may be provided for all of
the
apparatuses. The plenum may comprise a single confined space longer than the
length or
width of the pallet and the stack of containers thereon, the confined space
having a plurality
of openings for interfacing with the ventilation ducts of pallets. Each of the
openings may be
interfaced with the ventilation duct of a pallet, or if not all of the
available openings need to be
used, unused openings in the plenum may be sealingly blocked with a cover.
Sealing may be
accomplished in a similar manner as described above for the plenum and
ventilation duct.
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Further, the installation may comprise one or more rows of apparatuses, the
ventilation duct of each pallet interfaced with the ventilation duct of at
least one neighboring
pallet in the row. The row can be any length and there may be any number of
pallets and
stacks of containers thereon in a row. Thus, the ventilation duct of one of
the apparatuses in
the row is in fluid communication with the low pressure plenum, and the
ventilation ducts of
the other apparatuses in the row are sealingly engaged and in fluid
communication with the
ventilation duct of a neighboring apparatus in the row. Sealing may be
accomplished in a
similar manner as described above for the plenum and ventilation duct. The
ventilation ducts
in the pallets between the plenum and a last pallet in the row would be open
on opposed
sides (or one side and the bottom in an embodiment where the low pressure
plenum is below
the first pallet) and the ventilation duct of the last pallet would be closed
on the bottom and all
sides except the side in fluid communication with the neighboring ventilation
duct.
The number of apparatuses in a row making use of a single low pressure plenum
may depend on the strength of the low pressure plenum. As the row gets longer,
the ability of
the plenum to draw air through the last apparatus in the row is reduced.
Further, apparatuses
on a row that are situated further from the plenum may experience less air
flow therethrough
than those closer to the plenum. Therefore, there may be a limit to the number
of
apparatuses in a row. Rows containing from 1 to 4 apparatuses (i.e. 1 to 4
pallets with
corresponding containers stacked thereon) are preferred.
In one embodiment, the installation may comprise a low pressure plenum
situated
beneath the floor of the room and running a length (or width) of the room. The
plenum may
be located at one wall of the room. The pallets may be placed over apertures
in the floor
above the plenum, the apertures sized so that the bottom of the pallet may be
sealed on the
floor of the room. Air may thus be drawn down through the bottom of the
ventilation duct of
the pallet. One side of the pallet may be sealed against the wall of the
installation, and the
other sides of the ventilation duct sealed with longitudinal support members
or a blocking
member, or a blocking member on the last pallet if a row of apparatuses is
used. This
embodiment is particularly suited for repurposing existing facilities, for
example tobacco
drying kilns.
Corridors may be provided between rows of apparatuses in the installation.
Corridors
permit access to all of the apparatuses in a row to enable inspection and
sampling of the
foodstuffs and servicing of the apparatuses. Alternatively or in addition,
various sensors
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and/or cameras may be installed in the installation to provide real time
information about the
status of the apparatuses and the foodstuffs drying therein. Foodstuffs may
thus be
harvested directly in the apparatus as the containers may never need to be
removed from
the pallet throughout the drying process.
The method of drying foodstuffs comprises providing the foodstuffs in a
plurality of the
containers in the installation as defined above, controlling temperature,
relative humidity or
both temperature and relative humidity of air in the room, and drawing the air
in the room
vertically down past the foodstuffs until the foodstuffs are dried. The
temperature may be
controlled to any desired temperature and will depend on the type of foodstuff
being dried. A
temperature is in a range of from 2-20 C is generally suitable. A temperature
in a range of
from 3-15 C, especially 5-10 C, is particularly suitable for drying grapes in
the Appassimento
style. Maintaining a constant temperature is usually desirable, but for some
applications
providing a temperature gradient over time may be suitable. Relative humidity
also may
depend on the foodstuff being dried. A relative humidity in a range of from 40-
90% is
generally suitable. A relative humidity in a range of from 60-80%, especially
65-75%, is
particularly suitable for drying grapes in the Appassimento style. The air
flow rate through the
stack should be balanced with the height of the stack to provide uniform
drying throughout
the stack. The air flow rate may be in a range of 0.1-2 Ukg/s, or 0.2-1 Ukg/s.
Where a fan is
used to provide low pressure in the plenum, the air flow rate through the
stack may be
controlled by controlling the speed of the fan. Other air flow rate
controllers known in the art
may be used.
The time required to dry the foodstuff to the desired level is highly
dependent on the
particular foodstuff being dried. It is generally an advantage that the drying
time for a
particular foodstuff may be shorter while maintaining quality and consistency
of the
foodstuffs. When the foodstuff comprises berries, for example grapes, useful
in the wine
industry, the berries are generally dried until a certain Brix level is
achieved. Total soluble
solid (TSS) is the sugar content of an aqueous solution and is expressed as
degrees Brix
( Bx). One degree Brix is 1 gram of sucrose in 100 grams of solution and
represents the
strength of the solution as percentage by weight (1)/0 w/w). Grapes generally
start at a Brix
level in a range of about 19-23 Brix, and the target for the drying process is
usually at least
25 Brix, preferably 25-30 Brix, for example 28 Brix. For berries, e.g. grapes,
the time to
reach this level may be less than 120 days, for example from 7-115 days. This
represents a
significant shortening in time in comparison to traditional Appassimento
drying methods. One
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advantage of the present process is to be able to customize and adjust the
drying process,
so shorter or longer drying times than the traditional 100 days may be used
depending on the
desired end result.
Exemplary foodstuffs that may be dried include fruit (e.g. berries, apples,
oranges),
vegetables (e.g. carrots), tubers (e.g. potatoes) and herbs (e.g. ginseng).
The present
invention is particularly useful for drying berries (e.g. grapes,
strawberries, raspberries, blue
berries, cherries), especially grapes.
In another aspect, the present invention may be used to process foodstuffs in
a
manner other than for drying. Thus, instead of or in addition to drying the
foodstuff, the
foodstuff may be otherwise processed, for example cured, cooled or treated
with
gas/fumigant. In one embodiment, a foodstuff (e.g. sweet potatoes) may be
cured at high
heat (e.g. 29 C) and high humidity (85-95%) in an apparatus or installation of
the present
invention to cure the skin of the sweet potatoes to prevent moisture loss.
The present invention may provide one or more advantages. For example, the
apparatus is very modular and can be adapted to large or small operations and
is adaptable
to different harvest conditions and winery requirements. The modularity also
permits
adaptation to existing facilities, for example tobacco drying kilns, thereby
potentially reducing
capital and start-up costs. The drying process is controllable and adjustable
leading to more
consistent product from year to year. Mold development is controllable thereby
reducing crop
loss due to mold. Drying times of the foodstuffs may be quicker, which is
useful especially in
the wine industry where vintners may be able to harvest earlier to avoid
inclement weather or
climatic conditions and still get consistency and quality. Grapes are dried
uniformly and
efficiently in the Appassimento style, without comprising the grapes' final
quality, allowing for
consistent production of a premium value-added wine independent of
meteorological
conditions. Further, the taste of wines produced from berries dried in
accordance with the
present invention may be improved, in part because spiders, earwigs and lady
bugs may be
largely eliminated from the berries before the berries are crushed. It has
been surprisingly
found that spiders, earwigs and lady bugs would migrate out of the berries
during the drying.
Furthermore, bottle yields may be as high as or higher than 500 bottles of
Appassimento
wine per ton of grapes with a drying cost as low as $1 CDN per bottle, making
the production
of such wines affordable. Labor costs are also reduced because less manual
labor is
required to dry the foodstuffs.
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. .
Further features will be described or will become apparent in the course of
the
following detailed description.
Brief Description of the Drawings
For clearer understanding, preferred embodiments will now be described in
detail by
way of example, with reference to the accompanying drawings, in which:
Fig. 1A depicts a schematic of a side view of a drying apparatus comprising a
vertical
stack of reusable plastic grape holding baskets supported on a pallet in fluid
communication
with a low pressure plenum adjacent to the pallet;
Fig. 1B depicts Fig. 1A with sides of the stack sealed against air flow into
the stack
through the sides of the baskets;
Fig. 1C depicts a front view of Fig. 1A;
Fig. 1D depicts a top view of Fig. 1A;
Fig. 1E depicts a pallet used in the drying apparatus of Fig. 1A;
Fig. IF depicts a front view of the low pressure plenum of Fig. 1A;
Fig. 2 depicts an installation comprising a plurality of rows of drying
apparatuses,
each row of apparatuses comprising a plurality of apparatuses in fluid
communication with at
least one neighboring apparatus, and each row of apparatuses in fluid
communication with
the same low pressure plenum;
Fig. 3 depicts another embodiment of an installation comprising a plurality of
apparatuses in fluid communication with a low pressure plenum below the
apparatuses so
that air flows out the bottom of the apparatus;
Fig. 4A depicts a graph showing titratable acidity for different drying
conditions for
three grape varieties;
Fig. 4B depicts a graph of pH values for different drying conditions for three
grape
varieties;
CA 02828028 2013-09-20
Fig. 5A depicts a graph of malic acid values for different drying conditions
for three
grape varieties;
Fig. 5B depicts a graph of lactic acid values for different drying conditions
for three
grape varieties;
Fig. 6A depicts a graph of acetic acid values for different drying conditions
for three
grape varieties;
Fig. 6B depicts a graph of acetaldehyde values for different drying conditions
for three
grape varieties;
Fig. 7A depicts a graph of glucose values for different drying conditions for
three
grape varieties;
Fig. 7B depicts a graph of fructose values for different drying conditions for
three
grape varieties;
Fig. 8 depicts a graph of ethanol values for different drying conditions for
three grape
varieties;
Fig. 9 depicts a graph of glycerol values for different drying conditions for
three grape
varieties;
Fig. 10A depicts a graph of ammonia nitrogen values for different drying
conditions
for three grape varieties;
Fig. 10B depicts a graph of amino nitrogen values for different drying
conditions for
three grape varieties;
Detailed Description
Apparatus:
Fig. 1A, Fig. 1B, Fig. 1C, Fig. 10, Fig. 1E and Fig. IF depict one embodiment
of a
drying apparatus 1 comprising a vertical stack 5 of fifteen rows of grape
holding baskets 10
(only one labeled). As best seen in Fig. 1D, there are five baskets 10 per row
of baskets in
the stack 5. The baskets 10 comprise a plurality of side wall apertures 11
(only one labeled)
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and bottom apertures 12. Each basket 10 has an open top. The baskets 10 are
configured to
nest on top of each other and sized to provide a rectangular cluster of five
baskets when
arranged as shown in Fig. 1D. The stack 5 is supported from beneath by a
pallet 20. Details
of the pallet are shown in Fig. 1E. A ventilation duct 21 defined by the
pallet 20 is in fluid
communication with a low pressure plenum 30 situated beside the pallet 20. The
plenum 30
comprises a plenum aperture 31 (see Fig. 1F) and a foam sealing gasket 35
provides an air
seal between the pallet 20 and the plenum 30 where the ventilation duct 21 and
the plenum
aperture 31 interface. The plenum 30 is provided with a variable speed fan 37
at one end,
which draws air down the length of the plenum 30 past the plenum aperture 31
creating a
drop in pressure in the plenum 30. Air flowing through the plenum 30 follows
air flow path A
as seen in Fig. 1C, Fig. 1D and Fig. IF. It should be noted that the plenum 30
as depicted in
Fig. 1C is behind the stack 5 since the plenum 30 runs alongside the pallet
20. It should also
be noted that the plenum may be shorter and only as long as the side of the
pallet if there is
only one row of pallets in fluid communication with the plenum. As shown in
Fig. 1B, the
sides of the stack 5 are sealed against air flow by a blocking structure 7,
which may be
transparent to be able to view the baskets 10. Simply wrapping the sides of
the entire stack 5
with a plastic film provides a suitable air seal.
As seen in Fig. 1E, the pallet 20 comprises two substantially parallel side
boards
22a, 22b that form opposed sides of the pallet 20. Two substantially parallel
top boards 23a,
23b connect the side boards 22a, 22b proximate ends of the side boards 22a,
22b. A cross-
member board 24 parallel to and situated between the top boards 23a, 23b also
connects
the two side boards 22a, 22b to provide rigidity to the pallet 20. The cross-
member board 24
is specifically located to align with an interface 14 (see Fig. 1D) between
differently oriented
baskets 10 in a row of the stack 5. A support board 25 parallel to the side
boards 22a, 22b
and beneath the top boards 23a, 23b and cross-member board 24 connect the top
boards
23a, 23b to provide greater rigidity and stability to the pallet 20. The
rectangular pallet 20
thus defines the ventilation duct 21 defined by the side boards 22a, 22b and
top boards 23a,
23b, the ventilation duct 21 having an upper duct opening 27, two side duct
openings 28a,
28b and an open bottom. The bottom may be sealingly closed by the floor, while
one of the
two side duct openings 28a, 28b may be sealingly closed by a blocking panel
placed across
the opening, or may be in fluid communication with a ventilation duct of a
neighboring pallet.
The other of the two side duct openings 28a, 28b is in fluid communication
with the plenum
aperture 31 of the low pressure plenum 30. The ends of the side boards 22a,
22b and the
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outside edges of the top boards 23a, 23b have foam sealing gaskets affixed
thereto, one of
the foam sealing gaskets being the sealing gasket 35 between the plenum 30 and
the pallet
20, and the other providing a seal between the pallet 20 and a blocking panel
or a
neighbouring pallet. The top surfaces of the four boards 22a, 22b, 23a, 23b
form a sealing
support for the bottom of the stack 5 and define the upper duct opening 27,
which is in fluid
communication with the baskets 10 in the stack 6.
In operation, the fan 37 draws air through the plenum 30 along the air flow
path A
substantially parallel to the floor past the plenum aperture 31 thereby
causing a pressure
drop from the ventilation duct 21 to the plenum 30. Air thus moves out of the
ventilation duct
21 into the plenum 30 along air flow path B substantially parallel to the
floor and
perpendicular to the height of the stack 5. Movement of air along path B in
turn draws air
down through the stack 5. Air from above the stack 5 is thus drawn down along
air flow path
C, through an open top of the stack 5, and through the bottom apertures 12 in
the baskets
10. Air is permitted to diffuse between the baskets 10 due to the side wall
apertures 11, but
as shown in Fig. 1B, air is not permitted to be drawn in through the sides of
the stack 5 due
to the blocking structure 7 surrounding the sides of the stack 6. Sealing
engagement of the
bottom row of baskets 10 of the stack 5 with the top surfaces of the four
boards 22a, 22h,
23a, 23b of the pallet 20 ensures that air is drawn vertically from the top of
the stack 5
through the bottom of the stack 5 into the ventilation duct 21.
Installation:
Fig. 2 depicts one embodiment of an installation 100 comprising a room 110 and
four
rows 120a, 120b, 120c, 120d of drying apparatuses in the room 110. Each row
120a, 120b,
120c, 120d comprises four apparatuses 115a, 115b, 115c, 115d (only the
apparatuses in
row 120a labeled) of fifteen vertically stacked rows of five baskets for
holding foodstuffs (e.g.
grapes). The drying apparatuses 115a, 115b, 115c, 115d are in fluid
communication with at
least one neighboring apparatuses. Each row 120a, 120b, 120c, 120d of
apparatuses is in
fluid communication with the same low pressure plenum 130. Air flow through
the plenum
130 is provided by a variable speed fan 137 that draws air along air flow path
D past plenum
apertures spaced along an inside wall 132 of the plenum in the room 110. Air
is drawn
vertically down through each apparatus 115a, 115b, 115c, 115d as previously
described and
air flows through the ventilation ducts of each apparatus along air flow path
E (only one
labeled for row 120a). Opposing wall 133 and end walls 134a, 134b of the
plenum 130 are
13
CA 02828028 2013-09-20
formed by the walls of the room 110. A roof for the plenum 130 seals the top
and air drawn
by the fan 137 along air flow path D is eventually expelled through the fan
137 of the plenum
130. Thus, the plenum 130 is built into the room 110 using the floor and three
walls 133,
134a, 134b of the room 110 as the bottom and three sides of the plenum 130.
The roof and
the inside wall 132 of the plenum 130 are additional building materials to
complete the
plenum 130. An air conditioner 140 cools the room 110 when required, and
heaters 145 heat
the room when required, the air conditioner 140 and heaters 145 controlling
temperature and
humidity in the room. Corridors 160 are provided adjacent the rows 120a, 120b,
120c, 120d
for inspection, sampling and servicing the apparatuses.
Fig. 3 depicts another embodiment of an installation 200 comprising a building
210,
for example a tobacco kiln, retrofitted to house the installation. The
building 210 comprises a
subfloor 211 acting as a roof of a low pressure plenum 230. The subfloor 211
comprises a
plurality of spaced-apart grates 213a, 213b, 213c, 213d, 213e, 213f over which
a plurality of
drying apparatuses 215a, 215b, 215c, 215d, 215e, 215f are situated. With
reference to one
of the drying apparatus 215f, each drying apparatus comprises a pallet 220 and
a vertical
stack 205 of baskets for holding foodstuffs (e.g. grapes). The bottom of the
pallets 220 are in
fluid communication with the low pressure plenum 230, the plenum 230 being
defined by the
subfloor 211, floor 212 and opposed walls 214a, 214b of the building 210. A
fan 237 draws
air along air flow path F underneath the grates 213a, 213b, 213c, 213d, 213e,
213f and out
through the fan 237 in the wall 214a of the building 210. Air is drawn
vertically down through
the apparatuses 215a, 215b, 215c, 215d, 215e, 215f along air flow path G (only
one labeled
for apparatus 215f) directly through the grates 213a, 213b, 213c, 213d, 213e,
213f into the
plenum 230. An air conditioner 240 cools the building 210 when required, and
heaters 245
suspended from the ceiling of the building 210 heat the room when required,
the air
conditioner 240 and heaters 245 controlling temperature and humidity in the
building. An air
return conduit 250 located outside the building 210 permits air venting out
from the fan 237 to
be recirculated through the air conditioner 240 back into the building 210.
Corridors 260 (only
one labeled) are provided adjacent the apparatuses 215a, 215b, 215c, 216d,
215e, 215f for
inspection, sampling and servicing the apparatuses. If there is sufficient
room in the building,
the apparatuses 215a, 215b, 215c, 215d, 215e, 215f may be replaced with rows
of
apparatuses.
14
CA 02828028 2013-09-20
=
Method:
The present method was applied to the drying of grapes, in particular for
drying
grapes to the standards of the wine industry. Specifically, the present method
was adapted to
the Appassimento drying method.
Experimental Design:
An installation comprising a cold room and an apparatus as described in
connection
with Fig. 1A-F was used to dry three varieties of grapes ¨ Cabernet Franc,
Cabernet
Sauvignon and Merlot. The cold room was used to control the air temperature
and humidity.
The temperature was regulated by adding heat when required using heated lamps
connected
to a thermostat. The humidity was removed by condensing air on an evaporator
surface of a
cooling system and a humidistat was used to control the level of relative
humidity. A stack of
containers containing the grapes (three varieties x five repetitions) was
placed on the
apparatus. The apparatus was composed of a variable speed fan used to create a
pressure
drop in a plenum located adjacent to a pallet at the bottom of the stack of
containers, thus
15 producing a vertical airflow movement from the top to bottom of the
apparatus. To account
for the experimental design, eight apparatuses were built and placed in four
different cold
rooms. The grapes were dried until the total soluble solids reached
approximately 29 Brix.
The containers used to hold the grapes have an important role in the efficacy
of the
drying process. The container was a reusable plastic container (RPC), model
IPL 6411, 600
mm long x 400 mm large x 120 mm high. These RPCs were designed to be easily
folded,
stacked, transported and sanitized. Their construction was ideal for the
drying system as
their openings were designed and optimized to allow air to circulate through
and around a
product when placed inside.
Grape varieties selected were Merlot, Cabernet Franc and Cabernet Sauvignon.
These are the main varieties grown in the Niagara Peninsula region of Ontario,
Canada, and
the ones used most commonly for red wine production. These grapes were easily
available
and the varieties that would benefit most from an aroma improvement. The
grapes were
harvested in early September 2012 at a Brix level ranging from 21.7 to 22.6.
The grapes
were manually harvested and placed directly into the reusable plastic
containers. The
average mass of grapes in each container was 8 t 1.5 kg. After harvest the
grapes were
quickly placed in the drying installation with minimal handling, to begin the
drying process.
CA 02828028 2013-09-20
Different drying parameters were tested using a full factorial design, with
temperature,
relative humidity, airflow rate and grape variety as factors, in order to
determine the most
favorable drying conditions with respect to the variety. The drying efficiency
of each
combination of factors was assessed by recording the grapes' total drying
time, total weight
loss and measuring the quality of the grapes through evaluating their chemical
composition.
The drying parameters were as follows: temperature of 10 C and 5 C; relative
humidity (RH)
of 75% and 65%; airflow rate of 0.4 L/kg/s and 0.25 Ukg/s; varieties were
Cabernet Franc,
Cabernet Sauvignon and Merlot. In total, there were a total of 24
combinations, each
repeated five times.
Temperature and RH were monitored during the drying process. Weight loss and
total
soluble solids (TSS) as Brix were measured every two weeks. Grape quality
analysis was
conducted initially (at harvest), at approximately 25 Brix (mid-drying period)
and at 29 Brix
(final drying period). Grape quality analysis was performed to determine if
the drying process
affected the biochemical composition of the grapes. The grape quality analysis
comprised
the following evaluations: visual observation of mold, total soluble solids,
pH, titratable
acidity, acetic acid, malic acid, lactic acid, glycerol, glucose, fructose,
ammonia nitrogen,
primary amino nitrogen, ethanol, and acetaldehyde. Experiments were performed
according
to a factorial design. Data were analyzed using 4-way ANOVA with interactions,
and the
means were compared by the Tukey test at a significance level of 0.05 using
the XLSTAT
software (Addinsoft, France).
Weight loss and TSS values for the grapes were used to determine the kinetic
drying
rate and the time at which the experiment was to be completed, the objective
being to attain
29 Brix. Weight loss was measured every two weeks for each of the 15
containers in each
apparatus using a balance (OHAUStm, model Ranger v2 RC12LS, 12 kg capacity
0.0005
kg). TSS was also measured every two weeks using 15 berries randomly sampled
from each
of the 15 containers, in each apparatus. Berries were manually crushed in a
plastic bag and
the juice used to determine the TSS value by means of a refractometer
(AtagoTM, model
PAL-1). Data are presented as weight loss per day (%/d), TSS per day ( Brix/d)
and ratio of
Brix per weight loss (BNVL).
Ten berries from each plastic container were selected randomly and crushed
manually in a plastic bag and the juice was transferred to 15 mL centrifuge
tubes. The tubes
with juice were centrifuged (Sorvall ST 16 centrifuge, Thermo Scientific) at
5000 rpm for 15-
16
CA 02828028 2013-09-20
20 minutes and the supernatant was transferred into 2 mL microcentrifuge tubes
and stored
at -20 C for further chemical analysis. The remaining juice was used to
measure pH
(accumet AB15 Basic pH meter, Fisher Scientific) and titratable acidity
(Metrohem
autotitrator, model 848 Titrino Plus) by titration of 2 mL of juice diluted
with 50 mL of water
using 0.1 N NaOH to an endpoint of pH 8.2. Two readings were taken from each
sample for
total soluble solids and titratable acidity, and one reading was taken for pH.
Concentration measurements of 10 quality parameters were performed according
to
the manufacturer's specifications, using MegazymeTM assay kits and an
absorbance
microplate reader (BioTekTm E1x808) for samples at approximately 25 Brix
(midpoint) and
29 Brix (final point). For the initial samples taken at harvest, the
concentration of the 10
quality parameters was measured using a spectrophotometer (Smart Spec Plus Tm
from
BioRad) and Megazyme assay kits, and carried out according to the
manufacturer's
specifications, with the modification of scaling down the volumes by half. The
10 quality
parameters measured and Megazyme assay kits used to analyze their
concentrations are
listed in Table 1. For kits where the microplate assay protocol was not
available, the assay
volumes were scaled down 10 times in order to use the microplate reader. For
determination
of ethanol, malic acid and lactic acid, the samples were concentrated five
times (i.e., instead
of using 10 pL of sample, 50 pL was used, and the volume of water to which the
sample was
added was decreased by 40 IL to maintain the overall volume of solution). For
determination
of lactic acid the samples were concentrated 10 times using the same method.
Triplicate
analysis was performed on each sample and two data points were chosen for
analysis for
each sample.
17
CA 02828028 2013-09-20
'
Table 1. Kits utilized to determine concentration of 10 quality parameters
Quality Parameter Kit Name
Acetic Acid Megazyme K-ACET
Malic Acid Megazyme K-LMALR
Megazyme K-LMALL
Lactic Acid Megazyme K-LATE
Glycerol Megazyme K-GCROL
Glucose Megazyme K-SUFRG
Fructose Megazyme K-SUFRG
Ammonia Nitrogen Megazyme K-AMIAR
Primary Amino Nitrogen Megazyme K-PANOPA
Ethanol Megazyme K-ETOH
Acetaldehyde Megazyme K-ACHYD
For the quality analysis, samples were grouped together according to the
drying
temperature (i.e., 5 C and 10 C) and Brix measurement at the point of
chemical analysis
(i.e., at approximately 25 Brix, mid-drying period (MP), and 29 Brix, final
drying period (FP)).
For each group, the average and standard deviation was calculated and graphed
along with
the data from the initial harvest samples for each variety.
Results:
Drying was concluded when the grapes attained the targeted Brix level, which
was
29. The Brix level was monitored every two weeks by randomly selecting 10
berries from
each container in order to determine the total soluble solids level.
Drying time
Depending on the drying conditions and grape varieties, the time required to
dry the
grapes varied from 42 to 114 days (Table 2) and weight loss varied from 23% to
40% (Table
3). It is generally though that the Appassimento process should last up to 120
days with a
weight loss of up to 40% in order to fully allow the grapes to develop the
necessary
specificities that will produce a premium wine. From the three varieties
evaluated, Cabernet
Sauvignon meets most of the Appassimento requirements when dried at the lower
temperature and the higher RH. In order to establish the ideal Appassimento
drying
combination, with respect to the individual grape variety, it is importrant to
follow the grapes
beyond the drying process through to wine making. By creating wines from the
grapes after
the Appassimento drying it would be possible to determine the real
relationship between
18
CA 02828028 2013-09-20
these results and the development of flavors and aromas that contribute to the
creation of a
premium wine.
Table 2. Drying time in days (d) to reach the target Brix value
Condition Drying time to reach 29 Brix (d)
Cab. Cab.
Merlot Franc Sauv
C-65% RH 47 42 65
10 C-75% RH 65 57 96
5 C-65% RH 60 58 110
5 C-75% RH 78 92 114
5
Table 3. Weight loss (%) over the total drying period
Total Weight Loss (%) at
Condition 29 Brix
Cab. Cab.
Merlot Franc Sauv
10 C-65% RH 29 23 32
10 C-75% RH 33 25 40
5 C-65% RH 28 24 42
5 C-75% RH 28 31 35
Based on visual observation mold development was considered negligible.
Drying parameters
10
The overall effects of temperature, relative humidity and airflow on the
drying kinetic
of the three grape varieties are presented in Table 4. The drying kinetic is
presented as the
percent (%) of weight loss (WL) per day (d) and the Brix increase per day, as
well as the
ratio of Brix/weight loss (B/WL).
Temperature had a significant effect on the dependent variables. As
temperature
increased, WL and TSS increased as well. This response was expected, as higher
temperature allows for a higher respiration rate and also created an increase
in the partial
water vapor pressure of the grapes. Correspondingly, the effect of relative
humidity is also
significant, as higher relative humidity conditions resulted in less WL and
lower TSS values.
19
CA 02828028 2013-09-20
The airflow by itself did not represent a significant factor in the drying
process. This
may be a result of too small of a difference between the two airflow values
tested or due to
the water evaporation rate from the grapes being very small as compared to the
air's
capacity to absorb moisture.
The grape varieties did not respond the same way to drying, all three
varieties being
significantly different from each other. Merlot (M), due to the thin skin of
its berries, had the
higher rate of weight loss, followed by Cabernet Franc (CF) and finally
Cabernet Sauvignon
(CS) (Table 5). TSS values were also significantly different, with CF having
the highest rate
of Brix increase, followed by M and CS. One of the most important factors to
consider during
the drying process is the ratio of Brix increase per percentage of weight
loss (B/WL). A
higher B/WL value means that the percentage of weight loss that the grapes
must achieve
during drying in order to reach the targeted Brix level will be lower. A
higher B/WL ratio
results in a higher yield for the winery since the target Brix can be
achieved with less overall
weight loss occurring in the grapes. Cabernet Franc had the highest B/WL
ratio, followed by
M and CS, which means that CF is concentrating more sugar during the drying
process for
the same amount of WL, as compared to M and CS.
Table 4. Overall effects of temperature, RH and airflow rate on the drying
kinetic
Weight loss
Temperature ( C) (%/d) TSS ( Brix/d) Ratio (
BrixM/L)
10 0.504a 0.118a 0.236a
5 0.378b 0.085b 0.225a
Relative Humidity Weight loss
(%) (%/d) TSS ( Brix/d) Ratio (
Brix/WL)
65 0.487a 0.118a 0.242a
75 0.394b 0.086b 0.219b
Weight loss
Airflow (L/min-kg) (%/d) TSS ( Brix/d) Ratio (
BrixNVL)
0.25 0.445a 0.105a 0.234a
0.4 0.436a 0.098a 0.227a
For every independent variable, means with the same letters are not
significantly different at
alpha = 0.05.
Table 5. Effect of grape variety on the drying parameters
Variety Weight loss TSS (Brix/d) Ratio (Brix/WL)
CA 02828028 2013-09-20
(%/d)
Cabernet Franc 0.434b 0.127a 0.293a
Merlot 0.486a 0.106b 0.220b
Cabernet Sauvignon 0.403c 0.072c 0.178c
Means with the same letters are not significantly different at alpha = 0.05.
The interaction between temperature and weight loss and the resulting response
from
the different varieties was also significant (Table 6). At the higher
temperature, Merlot was
significantly more affected than the other varieties. At the lower
temperature, the difference is
less marked, however Merlot still has the higher rate, which is significantly
different from
Cabernet Sauvignon. As expected, the TSS increase rate was higher for Cabernet
Franc at
both temperatures but not significantly different from Merlot at low
temperature. Cabernet
Franc had the higher B/WL ratio at the higher temperature, significantly
different than the
other varieties but not different from what is observed for itself at low
temperature.
Correspondingly, similar results were observed for RH, with the exception that
there was no
significant difference between low and high RH for TSS development and B/WL
values for
CS, as well as B/WL values for M (Table 7). The two airflows were not
significantly different
in any of the cases but the response to airflow was significantly different
between varieties,
with M being the most affected through WL and CF for TSS and B/WL (Table 8).
Table 6. Interaction between temperature and weight loss
Temperature ( C) Weight loss (%/d)
Cab. Cab.
Merlot Franc Sauv
10 0.561a 0.491b 0.459b
5 0.410c 0.376'1 0.3481
Temperature ( C) TSS ( Brix/d)
Cab. Cab.
Merlot Franc Sauv
10 0.118b 0.152a 0.085c
5 0.095c 0.1026c 0.059d
Temperature ( C) Ratio ( BrixNVeight loss)
Cab. Cab.
Merlot Franc Sauv
10 0.209cd 0.315a 0.184d
5 0.23113c 0.270ab 0.173d
Means with the same letters are not significantly different at alpha = 0.05.
21
CA 02828028 2013-09-20
22
CA 02828028 2013-09-20
Table 7. Interaction between relative humidity and weight loss
Relative Humidity (%) Weight loss (%/d)
Cab. Cab.
Merlot Franc Sauv
65 0.536a 0.484b 0.442 ec
75 0.435c 0.383d 0.365d
Relative Humidity (%) TSS ( Brix/d)
Cab. Cab.
Merlot Franc Sauv
65 0.122b 0.150a O.081
75 0.090cd 0.104bc 0.063e
Relative Humidity (%) Ratio ( Brix/Weight loss)
Cab. Cab.
Merlot Franc Sauv
65 0.230bc 0.316a 0.180d
75 O.210 0.269b 0.177d
Means with the same letters are not significantly different at alpha = 0.05.
Table 8. Interaction between airflow and weight loss
Airflow (Umin-kg) Weight loss (%/d)
Cab. Cab.
Merlot Franc Sauv
0.25 0.491a 0.438b 0.4081'
0.4 0.481a 0.4301' 0.399c
Airflow (L/min-kg) TSS Brix/d)
Cab. Cab.
Merlot Franc Sauv
0.25 0.111b 0.129' 0.076c
0.4 0.101b 0.125a 0.068c
Airflow (L/min-kg) Ratio ( Brix/Weight loss)
Cab. Cab.
Merlot Franc Sauv
0.25 0.228b 0.299a 0.187cd
0.4 0.21213c 0.286a 0.169d
Means with the same letters are not significantly different at alpha = 0.05.
Titratable acidity and pH
23
CA 02828028 2013-09-20
The acidity level of juice or wine is a very important factor which will
affect the
composition, color, microbial stability, chemical reactions, structure, and
above all the
sensory perception and taste of the wine. Acids can be divided into two
groups: the fixed
acids (predominantly tartaric, malic, citric, and succinic), and the volatile
acids (almost
exclusively acetic acid).
The perception of acidity is also influenced by the type of acid present in
the wine,
with malic acid having the greatest perceived sourness of all the wine acids.
Acid thresholds
are increased by the presence of ethanol and also by sugar. The overall
sensory perception
of acidity is a function of a balance between all of these influences. Acidity
in wine can come
from those acids which are already present in the grape at harvest, or from
those which are
generated during winemaking or drying.
Acidity in wine is typically measured as titratable acidity (TA); chemically
the acids
influence total titratable acidity and pH.
Titratable acidity in grapes usually is in the range of 5 to 16 g/L. The pH of
grape juice
is ideally in the range of 3.0 to 3.8 at harvest. Both TA and pH could be
higher or lower
depending on the climate where the grapes are grown. Grapes which are grown in
cooler
regions tend to ripen later and at harvest they typically yield juice with a
lower pH and higher
TA than grapes grown in warmer climates. Typical harvest parameters for
Merlot, Cabernet
Sauvignon and Cabernet Franc in the Niagara Peninsula are a pH between 3.3 to
3.5 and a
TA between 5 to 7 g/L. In general, wines produced from a high Brix must, in
the range of
23.0 to 26.0, are recommended to also have a must TA ranging from 5.0 to 7.5
g/L and a pH
of 3.3 to 3.7.
In this study, the starting ranges of TA at harvest were consistent with the
expected
range of 5.0 to 16 g/L (Fig. 4A), with respect to the variety and typical
values for the Niagara
Peninsula region. Harvest values were on the higher end of the expected range,
which is
representative of a cool climate region, such as the Niagara Peninsula. The pH
levels were
lower than a typical harvest target value for the region but increased over
the course of the
drying process as TA declined (Fig. 4B). The results after drying were grapes
with pH values
very close to or within the ideal range for the region of 3.3 to 3.5. The
decrease in TA and
corresponding increase in pH during drying is likely a result of malic
respiration, as malic acid
is quickly consumed early in grape dehydration.
24
CA 02828028 2013-09-20
. .
Malic acid and lactic acid
At equal levels of each of the common wine acids, malic acid has the highest
perceived sourness, followed by tartaric acid, citric acid and lactic acid.
Malic acid is
biologically fragile and is readily metabolized by numerous wine bacteria in
the process of
malolactic fermentation. During malolactic fermentation, bacteria in the wine
convert malic
acid to lactic acid. This malic acid decrease is greater in conditioned drying
systems than
what is seen in natural drying systems. For wines grown in a cool climate, the
level of acidity
may be too high at harvest, resulting in overly tart wines. In many wines,
malolactic
fermentation can function as an important deacidification process. The
bacteria responsible
for the malolactic conversion are also responsible for producing compounds
which can
contribute to complex aromas and cream and buttery characteristics in the
wine. Malic acid is
typically in the range of 2 to 4 g/L in grapes at harvest and may be as high
as 6 g/L in grapes
from a cold growing region. Lactic acid is usually found in concentrations of
0 to 2.5 g/L in
wines.
The low values reported herein for the initial concentration of malic acid and
the
subsequent increase seen at the mid-drying point suggests that there might
have been an
error in the reporting of the initial values (Fig. 5A). The levels at the mid-
drying point are in
the range of normal values for malic acid in grapes and these levels decrease
over time by
the final drying point, which is expected as malolactic fermentation occurs.
Lactic acid in
wines is produced mainly as a result of malolactic fermentation; however,
lactic acid can also
be produced using other sources besides malic acid by the microorganisms
present, and
thus malolactic fermentation is measured by the disappearance of malic acid,
rather than by
the increase of lactic acid. An increase in lactic acid concentration was
observed between
the initial very low harvest values and the higher mid-drying point values
(Fig. 5B). There was
an overall decrease in concentration of lactic acid by the final drying point,
however this drop
was minor. The literature suggests that once lactic acid is formed, the levels
should not
undergo much change.
Acetic acid and acetaldehyde
Volatile acidity in wines is most often viewed as a spoilage characteristic
and includes
compounds such as acetic acid, acetaldehyde and ethyl acetate, which generate
undesirable
sensory characteristics (e.g. aromas of vinegar, oxidized, or nail polish
remover) at high
CA 02828028 2013-09-20
concentrations. In certain botrytized wines these acids can sometimes
contribute positively to
the aroma and flavor characteristics. Levels of volatile acidity are usually
monitored closely
throughout the wine making process, as concentrations can easily increase due
to microbial
activity. Volatile acidity can be veiled by high levels of sugar and alcohol
and also increases
the sensory perception of tannins and fixed acids.
Acetic acid is a by-product of microbial metabolism through the process of
wine
making and it eventually becomes the main volatile acid in the finished wine
with a typical
concentration range of 200-400 mg/L. The production of acetic acid during
fermentation is
not well understood. It has a distinct odor and like other volatiles it
evaporates quickly. The
production of acetic acid will result in the formation of other undesirable
compounds, such as
acetaldehyde and ethyl acetate. Acetaldehyde is a major component in the
production of
ethanol and it is normally reduced during fermentation. In some instances it
is still present in
wine at concentrations of 20 to 200 mg/L but the threshold ranges from about
100 to 125
mg/L. Both acetic acid and acetaldehyde can have negative effects on
fermentation, as they
are toxic to the Saccharomyces cerevisiae yeast.
Results for the present method show an initial increase in acetic acid levels
as a
result of microbial activity and metabolic processes (Fig. 6A). This is
followed by a decrease
in levels; acetic acid is a volatile and evaporates quickly which could
explain some of the
decrease in concentration, especially at the higher temperature. Production of
acetic acid
during wine making also slows down at pH levels over 3.2 and the pH in the
grapes was
increasing to this level or close to this level as the drying progressed.
Acetaldehyde levels
will increase as acetic acid concentration increases, since it is a by-product
of acetic acid
production, and an increase in acetaldehyde was visible by the final drying
point in all
varieties (Fig. 6B). The threshold for acetaldehyde ranges from 100 to 125
mg/L and the final
levels in this study are far below this concentration.
Glucose and fructose
Glucose and fructose are the two major sugars in grapes and comprise the
majority
of the soluble solids. These sugars are fermented into alcohol by the yeast.
Determining the
Brix does not accurately represent the sugar content in grapes and a
measurement of the
glucose and fructose levels can help to determine the fermentability of a
wine. Both fructose
26
CA 02828028 2013-09-20
=
and glucose are partially responsible to impart sweetness to grape juice, and
also to the wine
if still present after fermentation.
In unripe berries, glucose is the predominant sugar. In ripe berries, the
sugar content
is usually between 150 to 250 g/L with variability based on the variety and a
ratio of glucose
to fructose concentration that is close to one (1:1); however, climatic
conditions could affect
the 1:1 ratio. Glucose is metabolized slightly faster by the yeast during wine
making and
consequently the ratio declines gradually during fermentation.
Results showed that the glucose to fructose ratio was close to the expected
1:1 level
in the grapes at harvest in all varieties. Glucose was a bit higher in
concentration than
fructose, which is typical of grapes that are not completely ripe or those
grown in cooler
regions, and corresponds to the high initial TA levels seen (Fig. 7A and Fig.
78). The initial
combined sugar content for each variety was within the typical range of 150 to
250 g/L.
Overall there was a concentration effect of the sugars during drying, which
created an
increase in sugar levels. At the same time that sugar was being concentrated
through the
drying process, sugar was also being metabolized, and glucose at a slightly
faster rate than
fructose. Accordingly, the data shows that although both sugars increased in
concentration
as the grapes lost water, the fructose concentration increased at a faster
rate.
Ethanol
Ethanol in wine is produced through alcoholic fermentation and it is the main
by-
product of this process. Ethanol affects the flavor of a wine and also the
wine's body. Prior to
fermentation, the level of ethanol is almost zero in grape juice. Ethanol
content increases in
both control and tunnel-dried grapes. The effect of ethanol concentration due
to weight loss
in dried grapes is partial. The increase in ethanol during the drying process
is also due to
metabolic processes. As expected, results show an increase in overall ethanol
content due to
metabolic processes (Fig. 8). In two of the three varieties, there is a slight
drop in
concentration at the final point for the higher temperature treatment. This
could be due to the
stress of the higher temperature and evaporative nature of ethanol.
Glycerol
Glycerol is an alcohol found in trace amounts in sound grapes, typically less
than 1
g/L. It is produced as a by-product during sugar fermentation and is typically
found in
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CA 02828028 2013-09-20
concentrations of 4 to 12 g/L in table wines, and can be as high as 15 to 25
g/L in late
harvest wines. Glycerol is viscous and sweet, and the detectable sweetness
level in wine is 5
g/L.
The general perception is that glycerol contributes positively to the quality
of wine. It
has been suggested to contribute specifically to the mouth-feel, body and
texture properties
of wine, although no positive relationship has been established between
glycerol and mouth-
feel. Glycerol content increases in tunnel-dried grapes by the end of the
dehydration process
to 1.5 g/L.
Results in the present method showed initial glycerol levels to be in the
typical range
expected for grapes, less than 1 g/L (Fig. 9). In Merlot and Cabernet Franc
there was an
overall increase in levels by the end of the drying process, which is
consistent with the prior
art. In all varieties there was an increase in glycerol concentration from mid-
drying point to
final drying point at the higher temperature, and also at the lower
temperature for CF and CS.
Ammonia nitrogen and primary amino nitrogen
Nitrogen is a very important compound in wine production, as it is a nutrient
used by
yeast in the fermentation proces. Ammonia Nitrogen and Primary Amino Nitrogen
together
represent the total Yeast Assimilable Nitrogen (YAN), which is the total
nitrogen available for
yeast to use. A good fermentation process will result in good alcohol
production. If there is a
deficiency of nitrogen in the must, then fermentation will not proceed without
problems,
including stuck fermentation and the potential production of hydrogen sulfide,
which has a
rotten egg odor. Additionally, if there is too much protein present then there
could be
clarification issues with the wine.
Ammonia nitrogen is the primary form available for yeast to metabolize and is
usually
present in a range of 24 to 209 mg/L in grapes. Generally yeast need at least
150 mg/L for
YAN requirements and 200 to 250 mg/L is preferred. As stress variables
increase, the YAN
concentration needed in the must will also increase. Stress factors include
temperature
extremes and high Brix .
Results in the present method were highly variable between varieties. Overall
there
was likely a concentration effect occurring during the drying process, along
with some
metabolic activity (Fig. 10A and Fig. 10B). Initial levels were overall quite
low in the grapes
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and the values at the end of the drying process were still low, however VAN
requirements will
vary depending on the winemaker and the specific wine being produced.
The most promising combination of drying parameters in terms of total
Appassimento
wine yield produced from the dried grapes, would be to use Cabernet Franc at a
faster drying
rate; in this case the best parameters were 10 C and 65% RH. However, a faster
drying time
may be viewed as contrary to the spirit of the Italian Appassimento wine
making process,
since the hallmark flavors and aromas may not have adequate time to fully
develop in a very
fast drying process. A slower drying process would require a low temperature
and a higher
relative humidity; for this study the parameters to create a slower drying
time were 5 C and
75% relative humidity.
Results showed that the Appassimento drying principle is variety related.
Cabernet
Sauvignon was naturally a slower drying variety than Cabernet Franc and
Merlot, for the
particular harvest year.
The Appassimento process particularly benefits red wine made in cooler
climates,
however this method is not a miracle cure for bad quality grapes. The
harvested grapes
going into the Appassimento process must be of high quality and dried
consistently to
produce a premium wine.
The novel features will become apparent to those of skill in the art upon
examination
of the description. It should be understood, however, that the scope of the
claims should not
be limited by the embodiments, but should be given the broadest interpretation
consistent
with the wording of the claims and the specification as a whole.
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