James:
I am sure the readers are interested in the way that industrial produced freeze dried foods are made. I was a kashrut masgiach (kosher supervisor) at a major freeze dry producer in the United States before I emigrated to Israel. Mashgichim are flown all over the world to places where there is no Jewish community to certify the kosherness of foods for consumption by Jews. (The laws of kashrut are much too complex to describe here). The plant I certified had two major types of chamber one that was bus-sized and another that was the size of a minivan. Trays were fed in by an electrical railroad placed on the floor, hundreds if not thousands of pounds were freeze dried at a time. The chambers start out at below freezing when the vacuum is applied and as the time passes (the program depends on the food) the temperature is raised to (again depending on the food and its temperature tolerance) up to around 150° Fahrenheit. Freeze drying is simply quickly subliming away all of the water, the same thing that happens in freezer burn. Vacuum goes a long way to assist the subliming
process, at a vacuum of 20 mmHg, water will boil at 15°C stay below the boiling temp until almost all of the moisture is gone. Freeze drying keeps the food both feeling and tasting much fresher by maintaining the basic cellular structure of the food just desiccating. A standard food dehydrator which I have used at home radically changes both the mouth feel and flavor not to mention making for high re hydration times, there is also the question of how much nutrient is lost long term due to oxygen exposure. Vacuum pumps are available used for reasonable prices a coop might be able to purchase or build and run a small chamber. If anyone is feeling creative and builds their own freeze dry chamber, please write in with your results.
From David In Israel: How Freeze Drying Works
