What is Freeze Drying?

Freeze Drying is a hot topic on many forums and platforms today.

I’ve been preserving food for almost a half a century!! Having said that out loud scared me to death-:) A few years back, I got interested in freeze drying, probably through a blog or a podcast, but I just couldn’t bring myself to spend that amount of money for the two of us especially since I was already doing all the canning, fermenting and dehydrating that I thought was possible . I’ve successfully canned, dried and fermented foods for all our previous sailing trips so I didn’t really “need” another device to fill up my condo. However, good quality food and the knowledge of exactly what we put in our bodies have always been of great interest to me, so freeze drying kept on popping op. We actually bought a used machine on E-Bay, but got scammed out of $600 and received violent threads because we didn’t want to send the rest of the money!

Anyway, we spent another season sailing in the outer islands of the Bahamas, had wonderful food that we prepared at home and brought with us, but I kept on thinking that I can still do better with our food. Firstly, we prefer to go to the most remote places we can find where there are inevitably no restaurants – mostly not even inhabitants, and secondly, my constitution doesn’t do well with deep fried foods or preservatives, so I’ve always made as much food as I can from scratch with ingredients that I source locally.

When we returned to the USA after spending 18 glorious weeks on the boat, I again started looking into freeze-drying seriously and this time took the plunge and bought a Harvest Right Medium Freeze-Dryer. It has worked non-stop since the day we brought it home and everyday I’m still in awe at the quality of the end product as well as the retained nutritional value of the foods. And off course, music to any sailor or cruiser’s ears is the fact that you don’t need any refrigeration to store the food! I store most of the food we intend to eat within a reasonable amount of time in mason jars which I vacuum seal, but the longer term storage, and especially meat products, I store in mylar bags with oxygen absorbers to ensure the proper storage for longer term.

So, what is freeze-drying?

In layman’s terms, it’s the process of freezing food to a very low temperature, about -40F or colder, then vacuum freezing which sublimates the moisture and then drying the product until there is a very small percentage of moisture left. The less moisture, the better it stores for longer terms. Now, there are all the technical terms and details that can be Googled and Wikipedia explains it as follows: Freeze drying, also known as lyophilization or cryodesiccation, is a low temperature dehydration process that involves freezing the product and lowering pressure, thereby removing the ice by sublimation. This is in contrast to dehydration by most conventional methods that evaporate water using heat.

How does it work?

Most foods, including meats, vegetables, fruits and dairy are mostly comprised of water and this water content needs to be frozen, sublimated and then dried in order for the original product to retain about 98% of it’s nutritional value as well as retain the texture and color it had before the process. So the process in easy terms are as follows:

1. Freezing: The product is frozen under atmospheric pressure to about -40F.
2. Vacuum-freezing: Also known as proper freeze-drying, this is the sublimation step in which frozen free water is removed.
3. Drying: Also known as desorption drying, it’s the drying of products to their desired humidity by removing the remaining bound water.

Are Freeze-dried foods healthy?

Freeze-dried foods are without a doubt the healthiest way to preserve food. In fact, freeze-drying is becoming one of the most common dehydration methods due to its numerous benefits.

As a result of the process of freeze-drying, most (about 98%) of the nutritional value of the food is retained and the color, flavor and structure of the food is also remarkably preserved.

Studies show that compared with other drying methods, freeze-drying is the most effective at retaining antioxidants, such as anthocyanins, flavonoids, and ascorbic acid or vitamin C.

Additionally, given that decreased water activity inhibits the growth of most bacteria, yeasts, and molds, by removing a product’s water content, freeze-drying helps prolong a food’s shelf life.

Lastly, removing a product’s water content leads to a reduced volume and weight, making it easier to handle, store, and transport. The most common ways to store freeze-dried foods are glass, metal cans and mylar bags. If stored properly, these foods can last up to 25 years, which also makes it desirable as an emergency food supply and off course a great addition to any sailor’s pantry.

Foods that can be freeze-dried

Freeze-dried foods are often used for hiking, camping, space exploration, emergency and survival applications, sailing and cruising as well as military rations. They are preferred over regular foods due to their light weight, long shelf life, portability, and ease of preparation. Most foods only need water to reconstitute, while fruits and veggies are often consumed without any reconstitution.

Here’s a list of some of the foods that can be freeze-dried (in my opinion, most foods can be freeze-dried with great success):

• Fruits: strawberries, apples, blackberries, bananas, pears, oranges, and fruit puree
• Vegetables: almost all vegetables, such as carrots, asparagus, mushrooms, peppers, pumpkin, and tomatoes
• Meats: beef, fish, chicken, eggs, pork, turkey, and shrimp
• Grains: cooked rice, beans, pasta, quinoa, and polenta
• Legumes: cooked beans, lentils, peas, and tofu
• Frozen meals: whole meals like soups, stews, chili, and snacks
• Beverages: milk, juices, coffee, and tea for instant drinks
• Spices: ginger, oregano, mint, basil, and garlic
• Sweeteners: maple syrup for sugar powder

I’ve experimented with yogurt, and many different fully cooked meals and soups and they all work amazing. I haven’t done any syrup since honey is not recommended and supposedly makes a big mess in the drier.

Foods that cannot be freeze-dried

Very oily foods: Freeze-dryers extract water from the food, but the oil will remain in the food. Some foods don’t react well because of this. Pure butter, peanut butter and chocolate do not freeze dry. However, if these items are included in other foods, they freeze dry just fine.

Honey, syrups and jams: These foods make a sugary mess when freeze dried and can’t be reconstituted.

Bread, cake and muffins: These foods can be freeze dried, but reconstituting such foods in a bowl of water makes for a very soggy texture. However, when reconstituted properly, things like sliced bread, banana bread, pound cake and turkey stuffing turn out perfectly. Some of the items need to be wrapped in a damp paper towel, while others need a spritz of water or a light steam.

How the freeze dryer works

Step 1: Fresh or cooked foods are placed on the shelves where they are frozen to -40F or colder. (in other words, you push the button and the machine does the work from here on-:)

Step 2: Once the food is frozen, the freeze dryer creates a powerful vacuum around the food. As the food is slightly warmed, the ice in the food sublimates and changes directly from a solid to a gas. That water vapor is then discarded.

Step 3: When completely dry, food is removed from the freeze dryer and sealed in moisture and oxygen proof packaging to ensure freshness until opening.

Step 4: When you are ready to eat the food, simply add water. It will regain it’s original fresh taste, aroma and appearance!

A word of caution: The process can take up to 48 hours and sometimes even longer. The expense is quite high if you’re only going to use it a few times a year. You need space to keep it since it is noisy, about the size of a small refrigerator and heavy. It also heats up the space where it is kept a few degrees, so consider your options before running out to purchase it.