Case Hardening
“Case hardening”
If the food is dried at a temperature that is
too high, the outer surface will harden by preventing moisture from escaping
from the center of the slice. This is called case hardening.
If drying takes place too fast, however
“case hardening” will occur. This means that the cells on the outside of the
pieces of food give up moisture faster than the cells on the inside. The
surface become hard preventing the escape of moisture from the inside.
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Figure 1-: process
of case hardening
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So many food can dry using the case
hardening process.
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Ex-: Fruits-:Apples,
pears, peaches, banana, strawberries, plums,pineapples
Vegetables-: Tomatoes, Carrots
Fish
and Meat
Dry oven is the most popular equipment
for the case hardening process. We can use trays in the oven to dry food.
We can’t use solid metal trays or cookie
sheets to dry food. Because air must circulate all around the food. So that
drying can take place from the bottom and the top at the same time.
When you selecting a material for trays,
be aware about following things.
v Don’t use galvanized Screen, aluminum, copper, fiber, glass or
vinyl.
v If you use copper material, it will destroy vitamin C in the food.
v Stainless Steel trays are the best.
When you drying food, their cellular
structure will begin to shrink and cells will smaller. But if that food face to
case hardening process, that food differ from normal dried food as follows.
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Fruits are easier to dry than vegetables.
Because moisture evaporate is easy and not as much moisture must be removed for
the product to keep.
If you pack case hardened
foods,
Moisture at the center of
the food may begin to travel very slowly through the thick layer of collapsed
cells at the surface of the slice. Then it will move into the air inside the
package where it condenses on the cooler packaging surfaces to form water
droplets. These water droplets are now available to support mold growth on the
dried product. Any mold growth will spoil the product and unfit for eating and
then it must be tossed.
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What you can do if you
experience case hardening…..
Suppose that case
hardening has occurred to your food item. There are few options to overcome
from that. You can try following things.
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You can refrigerated the food as soon as possible.
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You can eat as soon as possible(fish, fruits)
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You can Rehydrated at the correct temperature. (This method is
not always 100% effective).
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You can prepare another food item. ( even curry)
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How we can prevent
Case Hardening……….?
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Use correct temperature
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Using cooler drying at the start of the drying process.
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Product should be cut into small pieces prior to drying. (cut
pieces uniformly)
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Rotate trays.
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Check machines’ temperature regularly.
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