Why is freeze-dried food not much more popular?

Question

Freeze-drying seems to be the perfect method for food preservation to take on trips to the outdoors: is the most lightweight food can be, can be shipped around the world easily, the majority of nutritional value is retained, no preservatives are needed and most important, no energy, no electricity is required to keep it good, and it can last years. Just add water and mix to get kind of a smoothie. Seemingly it should be vastly superior to any other method of food preservation.

Why are other methods still much more popular, and easier to buy such preserved foods:

• canning
• soaking in solutions of large amounts of sugar or salt
• high-heat drying
• freezing
• fermentation

All these above methods seem not as good as freeze-drying, yet they are all much more popular on the market, and freeze-dried food seems to be quite a rare and obscure thing to buy.

There are some freeze-dried powdered fruits and vegetables on the market, but few and far in between, there is infinitely more vendors selling canned fruits and vegetables, which are heavy, don't last as long, and are often loaded with added sugar.

It's even more rare to find freeze-dried meat or fish for sale, but you can buy canned sardine almost everywhere. Canned food seems to be the most popular preserved food to take on hiking trips without cooking facilities.

Freeze-dried milk is kinda available, but also mostly for speciality milk like camel milk, normal cow milk is mostly heat spray dried, which not only doesn't have as much water removed so it doesn't last as long, but also the heat used damages some vitamins, so freeze-dried would be more nutritious and healthy.

You can buy an expensive freeze-drier and do it yourself at home, but given all the amazing benefits of freeze-dried foods, and almost no difference compared to fresh when making a smoothie, I find it strange commercial-made freeze-dried food is relatively rare to find for sale.

One might say that the canned version more resembles the original fruit or vegetable, but blenders and smoothies are very popular, so why not freeze-dried food?

The high cost of freeze-drying and thus the final price of the food being too high could be the reason, but there a lot of food intended as pet food sold freeze-dried. One usually have a higher acceptable price for food for their pets then themselves, so if the economy works for pet food, it should work for human food too. Actually the majority of freeze-dried food for sale online is pet food (although some of it could be fine to eat as humans too).

What is wrong with freeze-dried food, what is the reason it is not much more popular then it is, resulting in poor choice and very small amount of vendors selling it?

Answer 1

The answer is that it is very expensive to make compared to other forms of preservation, especially in the home. Canning can be done at home with nothing more than jars, lids, water and an oven. Smoking you need a fire and something to hold the meat. Freezing, you need a source of cold (which we usually didn't have until very recently in human history). Drying can be done at low or high heat, so you can use a fire, or even lay it out in the sun if your climate is warm and dry enough.

To freeze-dry you need both a vacuum unit and a heavy-duty refrigeration unit in one device. Freeze-drying is usually done by lowering the temperature below the triple-point and then lowering the pressure so that any ice formed sublimates. This is a very slow process for solid materials such as meats and vegetables, because removing enough of the water out of a lump of meat is difficult, relying on diffusion (in the order of micrometers/hour). For liquid formulations such as used in vaccines and similar materials it is much faster because the liquid can be spread out over the surface into a thin layer allowing the ice to sublimate rapidly.

Additional issues involve rehydration - this is slow for most meats (diffusion again) and often results in unpalatable food that is difficult to eat (chewy or hard) and is not particularly tasty. Vegetables and fruit that have been freeze-dried are much better (in my opinion) and can often be eaten in the freeze-dried state or rehydrated.

In my country (NZ) the majority of freeze-dried food is sold as food for hikers and hunters, it is relatively expensive per meal (~$8-12 per person/meal). It is generally sold as a pre-packaged meal designed to look like your average meal - some visible carbohydrates, some vegetables and often some strips of meat. It is not usually sold as a powder suitable for turning into a smoothie. In my understanding most vegetables might be suitable for this form of preparation, but most meats are not because of the structure of the myosin fibers in the muscle tissue and the connective tissues will not form powders, no matter how much they are dried (this is why they used to be used for things like bow-strings). Liver and sweet-breads might be some exceptions to this as they are much more homogenous in structure and don't contain much, if any, connective tissue.

Pet-food on the other hand can be lower quality and the pets tend to not care (as far as we can tell) about taste and texture so much as people do. Pet foods can also be manufactured to lower safety standards than foods for human consumption, these combined make it more affordable for the companies to freeze-dry pet foods.

Dairy products need to be heat-treated before or during the drying process to kill any contaminating micro-organisms. This is a process called Pasteurization, and is performed because milk can carry pathogens like Mycobacteria and Listeria. It is cheaper and easier to spray-pasteurize into a powder than it is to freeze-dry. In fact I think in most of the western world at least, that most milk is spray-pasteurized and then reconstituted to make the 2% (skim), 4% (regular) etc. milk that is bought in many shops.

Answer 2

This is an addition to @bob1's answer.

 no energy, no electricity is required to keep it good,

That's only part of the energy balance: the drying process takes a lot of energy.

Vaporization enthalpy of free water is 2.257 kJ/g. (Condensation of the water vapor may recover some of this.)

In contrast, heating water 0 °C -> 100 °C (or 20 °C -> 120 °C in a pressure cooker) takes 418.55 J/g, so a bit less than 1/5 of the energy needed to dry out that same amount of water. (The other ingredients have lower specific heat capacity) (The analogy to recovering vaporizaton latent heat here would be to use the heat released when the canned goods cool to pre-heat the next batch.)

Here a business that does freeze-drying as a service lists a rough guesstimate for freeze-drying a 100 kg load of strawberries, evaporating 88 kg of water with an energy consumption of 330 kWh if we disregard short-time storage which would be needed for other preservation processes as well. 330 kWh / 88 kg = 13.5 J/g water. (This is not only "free", unbound water but includes also a secondary drying stage that removes e.g. desorbed water which needs additional energy.)

Even if we say that canning has an energy efficiency of only 50 % (that should be reachable at home), that's still an order of magnitude less than the professional freeze drying at 100 kg scale.

 and it can last years.

As you have already discovered, that is not true for all dried products. Lipids are difficult to preserve. (freeze dried vs. e.g. vacuum dried does not matter). E.g. in whole milk powder the residual water is sufficient to allow the lipids go rancid within a few months. In contrast, skimmed milk powder lasts many months.

 Seemingly it should be vastly superior to any other method of food preservation.

No, see above. All these preservation techniques (including freeze drying) serve better or worse for different purposes. The idea is to apply each technique where it is most suitable.

canning

see above. "natural" advantage for food that is anyways cooked.

soaking in solutions of large amounts of sugar or salt

even less energy needed - but suitable only for specific foods. With sugar, in particular food that will be eaten with the added sugar.

high-heat drying

Whenever the food will anyways be heat-treated, this is an obvious option that avoids all inefficiencies of the cooling part of freeze drying.

freezing

Allows to preserve raw food. Energy needed depends on storage time: the longer the more. (Initial energy spent on freezing can be partly recoverd e.g. by thawing in the fridge)

fermentation

Often done to obtain particular, different food. I.e., sauerkraut to me is a different food from white cabbage. I also distinguish between wine and grape juice.

The same for curing, btw.