Food Preservation - The Different Methods of Freeze Drying
After mentioning freeze drying in the last blog, I got to thinking: How could you do it on a smaller scale, because it would actually be the best way to preserve many foods that you wouldn't really want to ferment necessarily. Like raspberries and blueberries, etc.
I had some experience with freeze drying in my lab at school. Only they don’t call it freeze drying in a lab. They call it Lyophilizing.
The me now would have looked that word up immediately, but when I went to school they kind of taught you that your teachers were the source of your information. And everyone said it was just another word for freeze drying.
(Which I didn’t look up either, come to think of it.)
Since the lyophilizer apparatus was in my office lab, I was asked for my keys more than once so that the professors could fill up their instant coffee jars when they got low. Yes they used the lyophilizer to freeze dry the coffee. One teacher had a Yuban jar on her desk, the other a Nescafé jar and another a Sanka jar, but they were all filled with coffee from my lab. Ha Ha.
Well when you use a lyophilizer you generally use dry ice to do the freezing and you pull a vacuum on these little round flasks that you put the liquid substance in that you are going to freeze dry. I never really understood how it worked at all. I only knew the procedure to do it.
So now I just looked up freeze drying for the home and the equipment looked more like a dehydrator than a lyophilizer. It was then that it hit me - what the heck does that word actually mean? And why don’t they just call it freeze drying instead of acting so knowing, like it’s a sort of special club that says “L-y-o- phil- ize”.
Well OK. I found out that yes it does mean freeze drying, but the purpose is the difference. Freeze drying is for preserving food and Lyophilizing means creating a substance that will readily take in a solvent and reconstitute totally. Industry used to call these substances lyophils.
Lyo means solvent. Phil means love or lover of and of course ize means to make or change to. So when you lyophilize something, you are making it so that you can put the water or some other solvent into it so you can fully reconstitute that thing. You are basically making a solvent lover. This is largely used in pharmaceuticals to make easy packaging and storage of substances.
When you just dehydrate something like food, you can never fully rehydrate it because of the structural damage that occurs because dehydrating is so gradual that tissues are stressed and stretch when they have differing degrees of water in them.
I used the lyophilization process to manipulate lipoproteins and fatty acids in the experiments I was doing as a part of my research at the time. It’s funny how deep you can get into things without even understanding what you are doing.
It’s not that I didn’t ask, but so many before me just did without understanding what they were doing either.
So this just presses home how important it is to actually look up words that you don’t understand until you do understand them. I am finding that it makes all the difference in the world. It creates clarity that you don’t even know was missing.
Now it’s about time I define these things even though you might have gotten impatient and looked these things up on your own. If you did, good on you. It is a good habit to get into, not passing by words you don’t understand.
Lyophilization or Freeze drying is a process where water is removed from something after it is frozen by the process of sublimation.
After quick freezing the substance at a lower-than-freezing-point temperature, preferably much lower, it is put under a vacuum. In this vacuum ice can be removed by sublimation. You probably have familiarity with evaporation where liquid water becomes water vapor or gas like in dehydration. Well sublimation is when a solid skips becoming a liquid first and just goes right into being a gas in the air.
Nature abhors a vacuum and the water vapor attempts to fill the vacuum leaving behind a dried item that has its structure intact except that now the surface has fine pores where the water vapor escaped.
Now because of those pores even more water can be pulled out of the surface when subjecting it to a vacuum again. This is called desorption.
Desorption comes from Latin sorbere to suck in, and de- means a reversal of, in this case. So basically more water is sucked out with desorption.
So altogether freeze drying/lyophilization is a process containing 3 smaller processes.
Quick Freezing
Sublimation (First Drying)
Desorption (Second Drying).
Previously I had gotten erroneous data that one could freeze dry with cold air flow. And there are appliances being sold under the name freeze dryer which claim to do that, but they are not true freeze dryers. They might be like a combo freeze dryer/dehydrator. But it would not be quick enough with that method to not distort the structure of the item being preserved. It really wouldn’t be much more than a dehydrator without being able to pull a vacuum.
This is probably the reason why, historically, the freeze drying of food was only done in industry because special equipment was necessary to be able to control temperature and atmospheric pressure.
I was pleased to find, however, that as of 2013 someone ventured into making home units. And presently there are four companies that provide true home freeze dryers. They are Harvest Right, Stay Fresh, Prep 4 Life and Blue Alpine. The size, capacity, electrical equipment and cost vary between brands and models.
I don’t usually mention brands, but there were very much cheaper looking “freeze dryers” from Temu, Walmart and Target that look like freeze dryers, but then again they also look like high quality dehydrators, too. I don’t want anyone getting fooled into thinking they are getting a freeze dryer when they are not.
The questions to ask regarding these units are how does it freeze and how does it create a vacuum? If it can’t do either, then it is not a freeze dryer.
Prices will probably come down as freeze drying at home is a relatively new possibility. When I did a simple Google search I found that the current price ranges from about $2000 to $5000 for a true freeze dryer.
Well, that is not completely impossible and would be a good investment if you did make a habit of having bumper crops of delicious healthy food.
This makes me picture a world where there is so much good food around that you have to give it away and nobody would go hungry, at least not around you. And with freeze drying it would be possible to send your extras to some poor country. Ha Ha. Freeze drying drastically lightens the weight of the substance because water is the heavy component, as well as preserving the food for 10 to 25 years.
For those of you who didn’t get that joke. It was a common thing for parents in my generation at least to tell you that you had to eat all your food and not waste it because there were starving kids in various overseas countries. And many wise aleck kids used to respond with, “Well, send it to them!”
Well, I hope you enjoyed learning about freeze drying and might at least think about expanding your home gardening ventures knowing that there are ways to preserve the fruits (and vegetables) of your labor.