Freeze Dry
Freeze drying removes moisture from food through vaporization, which turns water molecules into vapor. Freeze drying food affects its texture more than other preservation methods, like canning or freezing, but the nutritional value and flavor stay intact. Since freeze dried food is so light, it's great for taking on backpacking trips or storing in your Make an Emergency Kit. Read on for information on how to choose what to freeze dry and process it using one of several freeze-drying methods.
Contents
Steps
Preparing to Freeze Dry Food
- Choose the types of food you want to freeze dry. Foods that contain high amounts of water work best for freeze drying. Their structure remains intact after the process. These foods hold up particularly well:
- Fruits like apples, bananas, berries, persimmons and pears.
- Vegetables like potatoes, peppers, carrots, sweet potatoes and parsnips.
- After you're familiar with the process, try freeze-drying chicken breasts, cheese, and even entire meals, like spaghetti and meatballs. Any food that contains moisture can be preserved using the freeze-drying process.
- Choose the freshest food possible. Freeze drying food at the peak of its ripeness or freshness helps make sure it will taste good when it's reconstituted.
- Fruits and vegetables should be freeze dried when they are in season and fully ripe.
- Meat should be freeze dried right after it has been cooked and cooled.
- Full meals should be freeze dried as soon as they have been cooked and cooled. Don't freeze dry them after storing them in the refrigerator for a few days, or they'll taste like leftovers when you reconstitute them.
- Avoid freeze drying foods that won't taste good reconstituted. Berries and apples don't need to be reconstituted - the freeze-dried version of these fruits tastes good as it is. Freeze dried meat or spaghetti, on the other hand, will need to be reconstituted with moisture in order to be edible. Don't freeze dry foods for which this won't be possible.
- Bread is not a good choice for freeze drying since its texture is so dependent on freshness.
- Cake, cookies and other yeast-based foods are not good candidates for freeze drying.
- Process the food for freeze drying. Get the food ready to be preserved by doing the following:
- If applicable, wash and dry the food thoroughly.
- 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.
Freeze Drying Food with a Freezer
- Place the food on a plate or tray. Spread it out so that the pieces of food are not clumped together.
- Place the tray in the freezer. If possible, make sure the freezer is empty of other items.
- Don't open the freezer much while the food is freezing. This will slow the freezing process, and cause ice crystals to develop on the food.
- If you have a deep freezer, use it. The food should be frozen at the lowest temperature possible.
- Keep the food in the freezer until it has freeze dried. Over the course of about a week, the process of sublimation will take place, and all of the moisture will be removed from the food.
- Test to make sure the food is completely freeze dried by removing a piece and allowing it to thaw. If it turns black, the food is not freeze dried yet.
- Store the food. Once the food has completely freeze dried, place it in freezer storage bags. Push out the air, seal the bags, and store them either in the freezer, in your pantry, or in your emergency preparedness kit.
Freeze Drying Food With Dry Ice
- Place the food in freezer bags. Lay the bags out flat, so the food doesn't bunch up in one corner.
- Push out the air before sealing the bags.
- Make sure the bags are sealed airtight.
- Place the freezer bags in a large cooler. Cover the food with dry ice.
- Wear gloves and long sleeves while handling dry ice.
- If you have a lot of bags of food, alternate food bags and dry ice until the cooler is full.
- Place the cooler in the freezer. After 6 hours, cover the cooler with a lid. After 24 hours, check inside the cooler to see if the dry ice is still there. If it's gone, the food is ready for storage.
- Remove the bags of food from the cooler. Store them either in the freezer, in your pantry, or in your emergency preparedness kit.
Freeze Drying Food with a Vacuum Chamber
- Place the food on a plate or tray. Spread it out so that the pieces of food are not clumped together.
- Place the tray in the freezer and freeze until solid. If possible, make sure the freezer is empty of other items.
- Don't open the freezer much while the food is freezing. This will slow the freezing process, and cause ice crystals to develop on the food.
- If you have a deep freezer, use it. The food should be frozen at the lowest temperature possible.
- Place the frozen food in the vacuum chamber pulled to about 120 m Torr. Set the temperature to {{safesubst:#invoke:convert|convert}}.
- The sublimation process should be complete within a week depending on the set parameters.
- Check one of the slices after waiting the proper time to make sure the freeze-drying is complete.
- Place the food in air-tight containers for storage.
Reconstituting Freeze-Dried Food
- Remove the food from the package. Place it in a bowl or pot.
- Boil a few cups of water on the stove. When the water has reached a boil, remove it from heat.
- Pour a little of the boiling water over the freeze-dried food. It will begin to fill out as it absorbs moisture. If it seems to need more water, pour a little more over the food. Repeat until the food is fully reconstituted.
Tips
- The purpose of storing freeze-dried foods is reduce water activity and moisture content so microbial activity is stunted. Adding a silica gel pack helps reduce the chances of condensation and moisture inside the container.
Warnings
- Handle Dry Ice with care. It will burn your skin if it touches you.
- Be sure to keep the foods in their proper storage containers to avoid spoilage.
Things You'll Need
- Food items for freeze-drying
- Metal tray
- Home freezer or refrigerator/freezer combination
- Freeze dry vacuum chamber (virtis, nitro, millrock etc)
- Glass jars or resealable storage bags
- Masking tape or labels of any sort
