Method for improving the softness of raisins

A method for improving the softness of raisins in which the raisins are placed inside of a sealed, heated vessel with an excess of glycerin and allowed to stand for approximately sixteen hours. The method comprises the steps of increasing the moisture content of a quantity of raisins is increased to yield a quantity of hydrated raisins; applying a coat of glycerin to the hydrated raisins to yield a quantity of coated raisins; forming a six foot high column of the coated raisins inside of a heated vessel with an excess of glycerin; keeping the coated raisins inside the heated vessel for approximately sixteen hours; and periodically mixing the coated raisins with the excess glycerin during the sixteen hour period.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates to the processing of dried fruits to improve 
their softness retention characteristics, and more particularly to the 
infusion of raisins with glycerol. 
2. Background Information 
It is well-known that raisins and other dried fruits lose enough moisture 
over time to reduce their softness characteristics beyond desirable 
limits. This problem is especially pronounced when the dried fruit is 
mixed with a dry cereal, such as corn or bran flakes. Many methods have 
been disclosed for minimizing this problem. For example, U.S. Pat. No. 
5,439,692, discloses a method in which glycerol is infused into raisins 
under vacuum in order to improve the softness retention characteristics of 
the raisins. A problem with this technique is that it requires an 
apparatus capable of achieving and maintaining a reduced pressure of about 
35 mm of Hg. The reduced pressure requirement adds to the cost and 
complexity of the process for treating dried fruit with glycerol. What is 
needed is a simpler and less expensive method of infusing dried fruit with 
glycerol. 
BRIEF SUMMARY OF THE INVENTION 
Briefly, the present invention comprises a method for infusing glycerol 
into a dried fruit, such as raisins, that doesn't require a reduced 
pressure infusion apparatus. In the method of the present invention, the 
moisture content of a quantity of raisins is increased by soaking the 
raisins in warm water. A coating of glycerin is added to the hydrated 
raisins and the glycerin coated raisins are transferred to an infusion 
vessel. A column of the coated raisins that is at least approximately six 
feet in height is formed inside of the infusion vessel. While the column 
of the coated raisins is in the vessel, the vessel is maintained at 
approximately normal atmospheric pressure, at a temperature above 
approximately 100.degree. F., for a period of time that is greater than 
about fifteen hours. This period of time is referred to as the infusion 
period. Periodically during the infusion period, the coated raisins are 
mixed for short periods of time (e.g. three minutes). For example, the 
raisins might be mixed during three separate three minute intervals during 
the infusion period. After the infusion period is over, the raisins are 
removed from the vessel, washed with water and dried.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates a raisin infusion apparatus 10 for infusing raisins with 
glycerol. Glycerol is an edible three-carbon trialcohol having the formula 
HOCH.sub.2 CHOHCH.sub.2 OH. Glycerol is also referred to as glycerin or 
glycerine. The apparatus 10 comprises an infusion vessel 14, a rotation 
mechanism 18, a glycerol mixing mechanism 22 and a frame 26. A catwalk 28 
is positioned above the vessel 14 to provide a place where an operator can 
stand to monitor the loading of raisins into the vessel 14. The catwalk 28 
also provides support for the mixing mechanism 22 and other mechanical 
equipment. The mixing mechanism 22 comprises a mixing trough 30, an auger 
32 and a slide 34. 
A weigh belt 36 weighs the hydrated raisins and delivers them to the mixing 
trough 30 where glycerol is mixed with the raisins. The rotational action 
of the auger 32 mixes the raisins and the glycerol and conveys the raisins 
along the trough 30 to the slide 34. Generally, raisins are moved through 
the trough 30 at a rate of approximately eight short tons of raisins per 
hour. The slide 34 directs the raisins and excess glycerol into the 
infusion vessel 14 through the opening 38. 
The infusion vessel 14 is an air-tight multisided drum comprised of 
stainless steel, and which has a capacity of approximately 20,000 pounds 
of raisins. The infusion vessel 14 has the vertical inside height "h" of 
approximately nine feet. One side of the vessel 14 (preferably the top 
side) includes a large opening 38 that is used for adding and removing 
raisins to and from the vessel 14. An opposite side (preferably the bottom 
side) includes a smaller opening 42 which is used for cleaning purposes. 
The opening 38 is covered with a water and air-tight lid 46 and the 
opening 42 is covered with a water and air-tight lid 50, both of which are 
preferably bolted into place. 
The vessel 14 is constructed from two layers of stainless steel with a 
cavity positioned between the two layers (see FIG. 3). The cavity provides 
a space for warm water to flow around the circumference of the vessel 14, 
so as to warm the vessel 14. An inlet hose 52 and an outlet hose 53 
provide an inlet and outlet for the warm water respectively. A water valve 
54 controls the inflow and outflow of water to the hoses 52 and 53. The 
two-layer construction of the vessel 14 allows water to flow completely 
around the vessel 14 in an upper section 56 and a lower section 57, but 
not in a middle section 58. Another hose (not shown) connects the sections 
56 and 57 so that water can flow between the two sections. 
The rotation mechanism 18 allows the vessel 14 to be rotated 360 degrees 
about a horizontal axle 60. The frame 26 is comprised of stainless steel 
and functions to support the vessel 14 and the loading mechanism 22. 
Additionally, the frame 26 should be able to support at least thirty 
thousand pounds in the preferred embodiment. The mixing trough 30 has a 
length "k" of eight to twelve feet and which preferably provides at least 
approximately eight feet of length in which the raisins and glycerol are 
mixed before being delivered into the vessel 14. The top of the mixing 
trough 30 is positioned at a height "n" above the catwalk 28. Preferably, 
"n" is approximately 2.7 feet. Several mixing vessels 14 can be positioned 
underneath the trough 30 at fixed intervals. The vessel 14 has an inside 
height "h" (preferrably approximately nine feet) measured from the inside 
of the lid 46 to inside of the lid 50. 
FIG. 2 illustrates that raisins from the trough 30 are delivered to the 
slide 34 via a chute 70. The slide 34 is positioned to direct the raisins 
to the opening 38 in the vessel 14. The rotation mechanism 18 includes an 
hydraulic actuator which provides enough torque to the axle 60 to rotate 
the infusion vessel 14. A circle 80 (shown in phantom lines) illustrates 
that the vessel 14 can rotate 360 degrees about the axle 60. Typically, 
the axle 60 comprises a six inch stainless steel rod that extends entirely 
through the vessel 14. The apparatus 10 utilizes an overall height "k" of 
approximately twenty-two feet that extends from a floor 86 to an upper 
region 88. 
FIG. 3 illustrates a piece 100 of the vessel 14 taken from section 57 
(shown in FIG. 1). A cavity 104 is formed between an outer wall 108 and an 
inner wall 112. The cavity 104 provides the passageway for warm water to 
flow in, thereby providing a means for heating the vessel 14. This two 
layer construction extends around the entire circumference of section 57 
so that warm water can flow on all sides of the vessel 14 encompassed by 
section 57. Similarly, section 56 of the vessel 14 is comprised of the two 
layer construction shown in FIG. 3 so that warm water can flow on all 
sides of the vessel 14 encompassed by section 56. A reaction chamber 116 
comprises the space enclosed by the inner wall 112 (i.e. the chamber 116 
is the inside of the vessel 14). 
Referring to FIGS. 1 through 3, the method of improving the softness of 
raisins can be explained. In a first step, the moisture content of raw 
raisins is increased from approximately 9-14% to 20-24%. This is done by 
immersing the raw raisins in warm water at a temperature of approximately 
130-180.degree. F. for one to two minutes to yield the hydrated raisins, 
and then removing the excess water from the raisins. The warm hydrated 
raisins are then transported to the weigh belt 36, preferably by a 
conveyor belt. The weigh belt 36 weighs the raisins that pass in a given 
amount of time so that the weight of raisins per unit time is known (e.g. 
lbs/hr.). The raisins then enter the mixing trough 30 where they are 
coated with pure glycerin that has been heated to approximately 
160-180.degree. F. The amount of glycerin used is approximately 18 to 23% 
of the weight of the raisins being processed, and preferably about 22%. 
The proper amount of glycerin to use is automatically calculated from the 
weight of raisins per unit time provided by the weigh belt 36. The warm 
glycerin can be mixed with the raisins by any number of techniques, such 
as by spraying the glycerin on the raisins, but preferably, the warm 
glycerin is mixed with the raisins using the mixing auger 32. The mixing 
auger 32 runs longitudinally along the trough 30 as is illustrated in FIG. 
1. 
The mixing auger mixes the raisins and glycerin and moves the raisins and 
excess glycerin along the trough 30. The raisins and excess glycerin are 
delivered into the reaction chamber 116 inside the vessel 14 via the slide 
34 and the opening 38. The excess glycerin arises because not all of the 
glycerin added to the raisins in the mixing trough 30 (i.e. the 18 to 23% 
amount of glycerin) is immediately absorbed by the raisins. The glycerin 
that is not absorbed initially is the excess glycerin. 
The quantity of raisins added to the vessel 14 is sufficient to create a 
column (pile) of raisins in the reaction chamber 116 that is at least six 
feet high, and preferrably nine feet high. It is believed that a six foot 
or higher column of raisins is important to the method of the present 
invention so as to create a head pressure that is high enough to 
facilitate the infusion process. The inside height "h" of the vessel 14 is 
sufficient to permit the six foot or higher column of raisins to be formed 
inside of the vessel 14, and preferrably the column of raisins extends 
along the entire inside height "h". The term column of raisins simply 
refers to the orientation the pile of raisins assumes when the raisins are 
added to the vessel 14. It does not imply a symmetrical cylindrical column 
in the geometric sense. 
Before the raisins are added to the vessel 14, the vessel 14 is heated to 
approximately 100-160.degree. F. (preferrably 130.degree. F.) by warm 
water flowing in the cavity 104. After the raisins are added to the vessel 
14, the lid 46 is secured in place, preferably with a bolt-type mechanism 
90. The raisin/glycerin mixture is tumbled soon after it is added to the 
vessel 14 by continuously rotating the vessel 14 through the 360 degree 
circle 80 for several minutes. The vessel 14 is maintained at 
approximately 100-160.degree. F. (preferrably 130.degree. F.) for an 
infusion period of approximately fifteen to twenty-four hours, during 
which time the vessel 14 is periodically subjected to several minutes of 
rotation. The rotation ensures mixing of the excess glycerin in the vessel 
14 with the raisins in the column of raisins. Generally, at the end of a 
rotation cycle, the vessel 14 is positioned 180 degrees from its 
orientation before the rotation cycle was started (i.e. the top becomes 
the bottom). This ensures that the pressure effect of the six foot column 
of raisins is experienced equally by all of the raisins. 
After the infusion period, the raisins are rinsed with water to remove the 
excess glycerin. Preferably, after the raisins are removed from the vessel 
14, they are directed up an inclined conveyor belt so that the excess 
glycerin runs down the conveyor belt and is collected. At the top of the 
conveyor belt, the raisins enter a shaker where they are washed with a 
water spray so as to remove excess glycerin. The raisins are then 
dehydrated to reduce the moisture content to approximately 11-14% by 
weight. At this point the raisins are found to have absorbed glycerin in 
an amount of 12-16.5% by weight. Finally, the raisins are coated with 
vegetable oil, such as a medium chain triglyceride (MCT), available from 
companies such as Hulls America or Stephan Company, to reduce stickiness 
between the raisins. A preferred example of this process is given below. 
EXAMPLE 
Raw raisins with a moisture content of about 11-14% are dumped into a 
hopper, then metered into a rehydration tank where the raisins are 
submerged in hot water at a temperature of approximately 130 degrees F. 
The raisins stay inside the rehydration tank for 1 to 2 minutes. Once they 
exit they are blasted with air to remove unnecessary surface moisture. The 
combination of hot water immersion and air blast elevates the raisin 
moisture content to about 18 to 22%. 
The warm rehydrated raisins are then mixed with pure glycerin, which has 
been heated to a temperature of 170 degrees F., at a ratio of 22 lbs. of 
glycerin for every 100 lbs. of processed raisins. The mixture of glycerin 
and raisins is loaded into an infusion vessel with a capacity of about 
20,000 lbs. of product, through the top of the vessel. The vessel is 
preheated to approximately 130 degrees F. by warm water flowing in the 
sides of the vessel before the raisins are added. The top of the vessel is 
sealed and the heating of the vessel is continued during the entire 
duration of the infusion process (about sixteen hours). The mixture of 
glycerin and raisins form a column approximately nine feet high inside the 
vessel so that the head pressure will assist in the infusion process. 
After the top of the vessel has been sealed, the infusion vessel is rotated 
for about 3 minutes to ensure proper mixture of the materials. The 
rotation is stopped with the top of the vessel pointing vertically upward. 
After about five hours, the vessel is rotated for another three minutes, 
but this time, the rotation is stopped with the top of the vessel pointing 
vertically downward. After about ten hours, the vessel is rotated for 
another three minutes, and this time the rotation is stopped with the top 
of the vessel pointing vertically upward. After about 16 hours of infusion 
time the wet glycerated raisins are unloaded from the vessel, rinsed with 
tap water and dehydrated in a 3 stage continuous belt dryer at a 
temperature of about 170 degrees F. in the first stage, 140 degrees F. in 
the second stage and 70 degrees F. in the third stage. The drying process 
takes place in about 60 minutes. The finished product presents a glycerin 
content of about 12 to 16.5% by weight and 11 to 14% moisture. As the 
glycerated raisins come out of the dryer they are sprayed with vegetable 
oil, preferrably MCT, at a ratio of 1 lb. per 100 lbs. of glycerated 
raisins. 
In view of the description and example given above, the method of the 
present invention can be summarized as follows: 
1. The moisture content of a quantity of raisins is increased to yield a 
quantity of hydrated raisins; 
2. A coating of a humectant, such as glycerin, is added to the quantity of 
hydrated raisins to yield a quantity of coated raisins; 
3. A column of the coated raisins that is at least approximately six feet 
in height, is formed inside of a vessel, and excess glycerin is present 
inside the vessel; 
4. While the column of the coated raisins is in the vessel, the temperature 
of the vessel is maintained at a temperature above approximately 
100.degree. F. for a period of time that is greater than about fifteen 
hours. This period of time is referred to as the infusion period; 
5. Periodically during the infusion period, the coated raisins are mixed 
for short periods of time (e.g. three minutes). For example, the raisins 
might be mixed during three separate intervals during the infusion period; 
and 
6. After the infusion period is over, the raisins are removed from the 
vessel, washed with water and dried. The dried raisins may optionally be 
coated with a vegetable oil. 
The method of the present invention has the advantage that less glycerin is 
required to attain the final glycerin concentration in the processed 
raisins. Typically, a reduction of 10-15% in glycerin usage is realized 
with the method of the present invention. Additionally, the raisins 
display a more uniform glyceration level when treated according to the 
present invention. The method of the present invention is also more 
amenable to automation than methods of the prior art. 
In the description given above, a glyceration process for improving the 
softness retention characteristics of raisins has been provided. It should 
be appreciated that this same process can be used with other dried fruits, 
such as dried strawberries, dried cherries, dried blueberries or dried 
cranberries, to improve the softness retention characteristics of these 
other dried fruits. 
Although the present invention has been described in terms of the presently 
preferred embodiment, it is to be understood that such disclosure is not 
to be interpreted as limiting. Various alterations and modifications will 
no doubt become apparent to those skilled in the art after having read the 
above disclosure. Accordingly, it is intended that the appended claims be 
interpreted as covering all alterations and modifications as fall within 
the true spirit and scope of the invention.