Why is understanding Case Hardening important?
As moisture is removed from fruits, meat, or vegetables, their cellular structure begins to collapse and the cells become smaller. The result of this is the shrinking of the product as it dries.
If the heat is too high, in hopes of a faster drying time, “Case Hardening” will occur. This is when the outside of the food hardens and moisture remains trapped on the inside. This moisture is then unable to dry because it is encased in a hard shell.
This hard shell layer is much like a skin that can trap moisture inside the food product. It severely reduces the efficiency of the drying process and may prevent this trapped moisture from leaving the food.
Once this outer shell has formed, there is little that can be done to dry the product in a controlled manner. An additional problem is that a look at the case hardened product will look like it is dry. When you feel them and bend them, the slices actually appear dry enough to remove from the dryer and be packaged for storage.
After packaging, 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. It then goes 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. Of course, any mold growth will make the product unfit for eating and then must be tossed.
What you can do if you experience case hardening….
If, after your food has dehydrated, you realize case hardening has occurred, there are a few options you can try.
- You can refrigerate the food and use as soon as possible.
- You can freeze the food and use up in dishes that require cutting the food up.
- You can grind the food into a paste and rehydrate at the correct temperature. Note: this method is not always 100% effective.
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