Freeze-drying is a food preservation process where food is quickly frozen, and then the ice is turned into water vapour. It is then removed by placing the frozen food in a vacuum, resulting in it being dehydrated.
Normally freeze drying is done by professional companies with specialist equipment. But, it can be done at home.
What is the point of freeze drying food?
Freeze-dried foods are used by astronauts, campers, backpackers, food manufacturers, doomsday preppers and the military. You can buy freeze-dried foods for home use. For example, fruit pieces that you might find in some cereals and space ice cream. You can get entire freeze dried meals, as almost all foods can be freeze-dried.
Advantages and Disadvantages of Freeze Drying Food
- As the water is completely removed from the food, it is very light. This is why it is used by astronauts, campers and the military, as it is easier and cheaper to move around.
- Freeze-dried foods tend to retain most, if not all of their nutrients, taste, shape and size.
- You don’t need to refrigerate freeze dried food, and it can last for months or years.
- Freeze-dried foods can be rehydrated very quickly, unlike dehydrated foods.
- Freeze drying food is can be quite expensive due to the specialised equipment.
- Freeze dried food takes up almost as much space as fresh foods, while dehydrated foods take up less space.
Even though freeze dried foods can be expensive, they can come in very useful. You just simply rehydrate them with cold or hot water. Therefore, you can carry the food you need without worrying about having to keep it hot or cold. Their long shelf life also makes freeze-dried foods a viable option for emergency food stores.
How to Freeze Dry Food
Before we get in to how to freeze dry food, there is a little bit of preparation to do.
1. Choosing the types of food for Freeze Drying
As we said before, fruit and veg with high water content are the best ones to freeze dry, as are certain meats and fish. It is best to Freeze dry food at the peak of its ripeness or freshness. This is because it will taste as good as it possibly can when it’s rehydrated.
- Fruits and vegetables should be freeze dried when they are in season and fully ripe.
- Meat should be freeze dried after it has been cooked and cooled, as should full meals. Make sure you don’t freeze dry them after they have been in the fridge for a few days, or they’ll taste like leftovers when you bring them back to life.
You really don’t want to freeze dry foods that won’t taste good when they are reconstituted. Some foods, such as berries and apples don’t need to be reconstituted and taste nice as they are. However, meat or spaghetti, will need to be reconstituted with moisture in order to be edible. Examples of foods that cannot be reconstituted are bread, cake or anything yeast based. This is because their texture is altered by its freshness.
2. Get your food ready for Freeze Drying
- Wash and dry the food thoroughly if it needs to be
- Slice the food into small pieces. Cut apples, peppers, potatoes and other fruit and vegetables into small chunks, so that the moisture is easily removed.
How to Freeze Dry Food Using Different Methods
1. Freeze Drying Machine
The easiest way to freeze dry food is to use a freeze drying machine. These are a little bit bigger than a microwave and do all the hard work for you. Simply slice the food up and lay it on the trays, switch the machine on and let it do its thing. 24 hours later your food is perfectly freeze dried without any intervention from you.
Have a look at the video below to see how the Harvest Right Home Freeze Dryer works.
2. How to Freeze Dry Food with your Freezer
- Place the prepared food on a plate or tray making sure the pieces of food are not too close together or touching.
- Put the tray of food in the freezer. Ideally, the freezer should be empty of other items.
If you choose this method, do not open the freezer while the food is freezing. This is because it will slow the freezing process, and cause ice crystals to develop on the food.
A deep freezer, is best and the food should be frozen at the lowest temperature possible.
3. Keep the food in the freezer until it has freeze dried. It will take about a week for all of the moisture to be removed from the food.
To make sure the food is completely freeze dried. Remove a piece of it and allow it to thaw. If it turns black, the food is not freeze dried yet.
Once you are sure the food is completely freeze dried, put it in freezer bags. Make sure you push the air out before you seal the bags. You can now store them in your freezer, a cool dry cupboard or in your emergency preparedness kit.
3. How to Freeze Dry Food with Dry Ice
- Place your food in freezer bags and lay them out flat.
- Push all the air out of the bags before sealing them up.
- Make sure you seal the bag up airtight.
- Place the freezer bags in a large cool box and cover the food with dry ice.
- Put the cool box in the freezer.
- After 6 hours, put the lid on to the cool box.
- After 24 hours, check to see if you still have dry ice. If it has gone, the food is ready.
Remember to always wear gloves and long sleeves while handling dry ice.
4. How to Freeze Dry Food with a Vacuum Chamber
- Place your food on a plate or tray. Make sure you spread it out so that the pieces of food are not too close or touching.
- Place the tray of food in the freezer and freeze until solid.
- Place the frozen food in the vacuum chamber set to about 120 m Torr. Set the temperature to 10 °C (50 °F).
This process should take about a week depending on the set parameters. Check a piece of food after waiting the proper time to make sure it is properly freeze dried.
How to Reconstitute Freeze Dried Food
- Remove the freeze dried food from the freezer bags and put it in a bowl or saucepan.
- Boil some water on the stove.
- Pour some boiling water over the freeze-dried food. As it absorbs moisture, it will fill out. If it seems to need more water, pour a little more over the food. Repeat until the food is fully reconstituted.
What are your thoughts on freeze drying? Please let us know in the comments section below.