The Process of Freeze-Drying
Freeze-drying is a complex process of preserving fresh or already-cooked food by removing up to 98% of the food’s moisture, leaving intact the food’s texture, flavor, aroma and nutritional value.
The process requires that the fresh or cooked food be quickly frozen at temperatures as low as -50°C. The frozen food is then placed into a vacuum chamber. This vacuum chamber lowers the pressure, and raises the temperature to just about 0°C.
At this specific temperature and pressure, the ice crystals in the food evaporate into water vapor, bypassing water’s liquid form, through a process called sublimation.
This process preserves the cell structure and nutritional content survival food of the food, resulting in a product that, when rehydrated, very closely resembles the original food.
The process also prevents the water from being reabsorbed by the food and thus decreases its weight significantly.
Most food items such as fruits, vegetables and meats are well-suited to freeze-drying, and can be used for long-term food storage and preservation.
The Process of Dehydration
Dehydrating food is a food preservation method which has been used for centuries. Native Americans dehydrated their buffalo kills in their hunting camps to make it simpler to transport. Pemmican (a dehydrated concoction of buffalo meat mixed with fat and berries) was a staple of many of the nomadic North American tribes. This low-heat dehydration process involved either air drying (with nearby campfires), or sun drying strips of meat on drying racks.
Dehydrators are a modern method for slowly removing the moisture from food without actually cooking it. A drawback of dehydration is the limited amount of food which can be dried at one time. The positive aspect of dehydration is that this method of processing for food storage can be easily done at home.
How Do These Two Methods Affect the Food?
Freeze-dried foods preserve much of the original color, shape, aroma and freshness of fruits, vegetables and meats. Freeze-dried food does not usually contain additives or preservatives, so it remains true to its original form. And the look, texture and flavor of the food remains after re-hydration.
Unlike low-heat dehydration, freeze-drying allows for the preservation of pre-cooked meals, including recipes such as soups, stews, stroganoff, and the like. An obvious benefit is that since the meal was prepared in its entirety prior to freeze-drying, all you need to do is simply add water, then heat for a few minutes in order to create sumptuous meals.
Rehydrating freeze-dried food takes just a few minutes, simply by adding boiling water. Some foods, like many fruits and vegetables, need no re-hydration before eating.
Dehydrated foods shrink during processing as the moisture is removed. So the food item itself is considerably smaller than its original size.
The re-hydration time of dehydrated foods takes a bit longer than freeze-dried, but it stills tastes like the original form of the food. Some dehydrated foods contain added ingredients to enhance flavors or assist in preservation. As with freeze-dried fruits and vegetables, dehydrated fruits and vegetables can be eaten without any re-hydration.