Freeze Dry & Dehydration

Before we get into the nitty-gritty, let's first start off by learning the difference between the two...

Freeze-drying is a low-temperature dehydration process that involves freezing the product, lowering pressure, then removing the ice by sublimation. Because of the low temperature used in processing, the quality of the rehydrated product is excellent, and the original shape of the product is maintained[1].

Commercial_Freeze_Dried.jpg

Freeze Drying is so effective that it removes 98%-99% of the water from the food and has a shelf life of at least 25 years[4].

Drying or dehydration is, by definition, the removal of water by evaporation, from a solid or liquid food, with the purpose of obtaining a solid product sufficiently low in water content. Most commonly, heat is added to the food by hot air, which also carries the moisture away from the food. [2].

China-Industrial-Commercial-Food-Dehydra

Regardless of the process, the act of processing does change the nutrient value. Removal of water is not the only consequence of most drying operations. Other important quality-related changes in taste, flavor, appearance, texture, structure and nutritive value may occur in the course of drying. The extent of such changes depends on the process conditions[3].

Most dehydrated food has removed between 70%-95% of the water and has a shelf life of up to 15 years[4].

Nutrient changes
When you process any food, there will be nutrient changes, that doesn't always mean for the worse, processing simply changes the nutritional profile.  Where heat and air are used, this can be problematic due to volatile nutrients such as vitamin A & C that are sensitive to such processes.

particularpantry.com states that in reference to dehydration, the heat that causes the water to evaporate from dehydrated food, unfortunately, cooks some of the nutrients out too. This leaves dehydrated food with an average of 50%-60% of the original nutrients[5]. We don't have a clinical study or paper to validate their statement, I personally had heard it was 70% = 30% loss, this was many years ago and I haven't been able to find the source of that information today.

They go on to say that since freeze-dried food is preserved without using heat, the nutrients are almost perfectly preserved. Freeze-dried food retains 98%-99% of the original nutrients of the food[5].

The University of Missouri states that the nutritive value of food is affected by the dehydration process - vitamins A and C are destroyed by heat and air but don't go into detail about the average % of nutrient loss or retention[6]. 

Harvest Right, the Freeze Drier company state that the process of dehydrating affects the taste, color, and nutrition. Dehydrating destroys nearly half of the nutritional value. Freeze-dried food, in contrast, preserves nutrition and looks and tastes just like it did when fresh. They cite their source of this statement as an article called "How Dehydrated Food Works" where they state "Depending on how the food is prepared and dehydrated, losses of heat-sensitive vitamins like vitamin C and thiamin can be significant. Fruits like apples, apricots, peaches, and prunes lose about 6 percent of their vitamin A, 55 percent of thiamin, 10 percent of niacin and 56 percent of vitamin C" - the source of this information was Wiley Encyclopedia of Food Science and Technology, however, the link they provided didn't take us through to the specific claim, so we cannot validate that.

What does this mean to you as the pet parent?
Whilst at this time we can not verify a more accurate nutrient loss in dehydrated food, we can safely assume there is a nutrient loss so we would recommend that you do not use dehydrated food in place of unprocessed foods on a regular basis.