Have you heard about the freeze-drying process? Or how to freeze dry fruit with dry ice? Freeze-drying food, most commonly of fruits because of how quick they are to prepare, are becoming a popular method when you need to store food for emergency purposes.
If stored right at room temperature and at right location, a freeze-dried food can still be edible after a decade!
To know the wonders of freeze-drying, read this article on how to freeze dry fruits and how you can try it in your home. In addition, it has the benefits of freeze drying your food.
As it is sometimes called lyophilization, it is a chemical process of preserving the edibility of the food through freezing and then drying, hence, its name. In layman’s terms, freeze-drying is like the suspended animation of the food.
Basically, you remove all the moisture and water content of the food, but the chemical composition stays the same. Because you’re just removing the water, if you’re ready to eat it, just rejuvenate the freeze-dried food with hot water.
It is already proven in many accounts that after many years, a freeze-dried food still has its texture and taste as if prepared that same day.
If you have the necessary equipment, you can freeze-dry virtually anything! Fruits are number one on the list because they are easy to acquire, and the water content is easily sucked out.
For example, if you want to store meat through freeze-drying, you’d want to cook it first before freezing. This is because if you rehydrate a freeze-dried raw meat, it would still be raw.
The main reason why we preserve food for storage is to avoid spoilage and inhibit the growth of disease-causing bacteria.
In freeze-drying which has other names like lyophilization or cryodesiccation is a smart way to preserve a perishable food by freezing it and then reducing the atmospheric pressure.
Sublimation is the main chemical principle about freeze-drying and it makes the food shift from a solid phase into a gas phase without undergoing a liquid form (e.g. like naphthalene balls).
Normally, you place the food in a vacuum container that uses lower pressure. The first stage in the process is the pretreatment. For fruits, you may need to slice them into chewable bits, and for larger food like beef stew, you must need to cook it firsthand and wait to cool.
The second process is the freezing. This can be done in machines specific for the process alone, or you can use your freezer at home.
You will need to freeze the food to its lowest temperature where both the solid and gas phase can be both present.
The typical freezing temperatures are ranging from -50⁰C to -80⁰C and must need to be done rapidly and appropriately. This is the most crucial process because the food can be spoiled if you have done it wrong.
Drying follows the freezing process and is broken into two parts: primary and secondary drying. In the primary drying, most of the water is removed, and the pressure is lowered as controlled in a vacuum container.
Heat is also applied for the ice to sublime, thus removing the water content. Heat must be applied gradually because too much heat can change the chemical structure of the food.
The last stage is the secondary drying wherein you effectively remove the residual moisture from the primary drying. This is done by subjecting the food to higher temperatures like more than zero degrees Celsius. The estimated water content percentage after the process would then be at 1% to 4%.
How To Freeze Dry Fruit With Dry Ice
Dry ice (or cardice) is carbon dioxide in the solid phase. Freeze-drying food in this method is relatively faster than putting it directly into your freezer. The way to use dry ice is to prepare a large container, twice the size of the food you’re going to freeze-dry.
The food (in this context, fruit) that you should freeze-dry should never be in contact with dry ice, so you need to place it in a sealed plastic bag.
After you placed the food in the plastic bag then into the large container (the bottom base should already have one layer of dry ice), you can now cover the whole container with dry ice. Word of caution for this method is to always wear gloves
Dry ice should never be melted prematurely, and that’s why you will need to store it in a freezer. Dry ice can make the moisture evaporate from the food because the environment is already at zero humidity.
As the dry ice will sublime and gas will escape, you should punch holes on your large container.
Regularly check your container every 24 hours. You will know the freeze-dried fruit is ready when all the dry ice had sublimed. After that, the freeze-dried fruit is ready for storing.