Applications of Freeze-Dried Fruits in
Confectionary Products
From "The
Manufacturing Confectioner"/June 1989
In freeze-drying, moisture sublimes directly from the
solid state to vapor, thus producing a product with controllable moisture, no need for
cooking or refrigeration, and natural flavor and color.
INTRODUCTION
Freeze drying is a rather specialized segment of the food industry.
Many people may know of the general nature of freeze drying and some may even be familiar
with selective freeze-dried foods. Despite this, most people are not familiar with the
basic process of freeze drying.
That mystery should be cleared up now. Compare evaporative drying with
freeze drying. If one were to place an ice cube, which is the solid state of water, at
room temperature for an extended time, the ice would first melt to the liquid phase. If it
is left there long enough, the liquid will evaporate into the atmosphere and become the
vapor form of water. This transfer of liquid to vapor is what's known as evaporation.
Evaporative drying is what is occurring when conventional dehydrated fruits and
vegetabales are processed. The moisture present in the food item is in the liquid form,
and it is evaporated to the vapor state. Now, if one takes that same ice cube, the solid
state of water, places it in an extremely low vacuum and applies a little heat to
accelerate the process, the moisture from the solid state will sublime directly to the
vapor state and bypasses the liquid state. The technical terms for this phenomenon is
"sublimation and lyophilization". Commercially, the process is reffered to as
freeze drying and when heat is applied to make the process economically viable, it is
referred to as "accelerated freeze drying" (Figure 1).
Evaporative drying is done at atmospheric conditions. Consequently, as
the moisture evaporates from the cellular structure of the food, the atmospheric pressure
tends to collapse those cells. The end result is a relatively hard and shriveled piece of
food which will require a considerable amount of time to reconstitute. When food is
dehydrated by the freeze-dried method, there is virtually no pressure on the food during
the drying process under the high vacuum conditions. Thus, as the watter is sublimed
from the foods, the cellular structure does
not collapse and remains porous. Hence, it will reconstitute quite rapidly, merely with
the addition of water. In some cases, the heat applied during the conventional dehydration
process is enough to alter the natural flavor of the food and may even impart a slight
cooked note. With freeze drying, the moisture is being sublimed from the product while
it's in the frozen state which permits maintenance of the natural fresh fruit flavor.
ADVANTAGES OF FREEZE-DRIED FRUITS IN CONFECTIONERY PRODUCTS
Natural flavor
As discussed above, the freeze drying process is a very gentle process
and preserves the natural flavor of the food. In most cases, the starting raw material for
freeze drying will be fresh frozen fruits. This allows production of a freeze-dried fruit
containing less than 3 percent moisture which will have a very nice fresh flavor present.
With confectionery products, one proviso does exist that there must be sufficient moisture
present to activate and release the flavor to the taste buds.
Natural color
Here again, comparable to what was discussed on the fresh flavor,
freeze drying preserves the natural color of the fruit. This is an asset to labeling of
premium confectionery products in that one can achieve both flavor and color from the
natural freeze-dried fruit.
Moisture control
It is well-established that the moisture content of confectionery
products must be controlled within prescribed limits to avoid spoilage by fermentation.
Use of freeze-dried fruits fits this concept very well. Since the freeze-dried fruit
product is less than 3 percent moisture, one merely needs to add sufficient water to allow
blending of the material into the formulation. Often times, moisture is only added to