The Science Behind the Magic of Freeze Drying
Freeze drying is definitely a scientific process. It seems so simple, you “Freeze” and “dry” the food, but when I actually looked into what goes on it felt so complicated. Many people think freeze drying is the same as dehydrating but it’s actually a very different process. Freeze drying involves multiple smaller processes and has specific vocabulary, such as temperature, atmosphere, pressure (I’m still not sure what a militorr is), and sublimation. I will do my best to simplify it for you.
Freeze-Drying is like a 3 Act Play. In Act I the food is frozen; in Act II the food is basically sent to outer space (no air pressure, no heat); Act III finishes drying (and I mean drying like the Sahara Desert) and gets it ready for packaging.
Queue Act One: Food is loaded into the machine on trays and frozen. I mean frozen the regular way, not "born of cold and winter rain and mountain air combining". Frozen down to minus 50 degrees. Yes, you read that right…That is 50° below ZERO or 82° below "freezing". Once the food is THAT COLD, all of the water, liquid, fluid, moisture, H2O, whatever... has become ice crystals. It is important for the process to work properly that the ice crystals be not too big and not too small so that they can sublimate out of the food without affecting the texture of the food.
In Act Two the machine uses a vacuum pump to pull almost all of the atmosphere out of the chamber. So, now it's like we've sent the food into outer space. No warmth, no atmospheric pressure. Conditions are right for what scientists call "sublimation" drying (which is a word used here to describe when H2O skips the liquid phase and goes straight from solid ice to steam vapor). The machine ever so slowly warms just the trays to around -10° F. This is the tricky part. Because there is no (or very little) atmospheric pressure the temperature needed to turn the ice crystals into vapor (sublimate) is also very low, only about -20° up to +0°) As the temperature rises the ice crystals become vapor and condense onto the frozen chamber walls.
The Third and Final Act of the play, desorption drying, begins (the removal of bound water molecules). At this point the food is only mostly dry - about 95%. There is a big difference between mostly dry and completely dry. The machine now warms the trays further, while still maintaining the vacuum inside the chamber. It slowly warms the shelves to over 120° F. Now, because the bulk of the ice crystals are gone, the texture of the food remains the same no matter the temperature (up to 150°!). Once the sensors read no more vapor in the chamber, the play is over. The food is warm and dry and the chamber walls are covered in condensation ice.
What we are left with is food that is now “lighter-than-air” and crispy with flavors that have been intensified. What was once a chewy, gummy candy is now crunchy like a cheese puff. Taffies now melt in your mouth like cotton candy. Cold, creamy desserts like Ice Cream and Banana Pudding are now crispy like a cookie but once you put it into your mouth it begins to rehydrate on your tongue and you get the smooth creamy feeling of ice cream or pudding.
Note: Our Freeze Dried creations are not intended for long term storage. However, if stored properly your unopened candies should remain fresh for 3 - 6 months. Do not store in direct sunlight and keep in mind humidity is like Kryptonite to freeze dried food.