This is a question that we get quite often, so it might be more useful to explain it in a blog post 🙂
So, both processes are food preservation processes, used specifically for dog food (of course they are also used for human food, but our focus here is dog nutrition). Both processes remove moisture from foods and thus prolong their shelf life, but there are some differences.
First, let´s cover the basics:
AIR-DRYING is literally “drying with air”. The process depends on the machine, but generally the drying happens by circulating hot, dry air. The food/ingredient is fresh (not frozen). Through the process, the moisture evaporates, so the finished product is dry and it usually loses a bit of the shape (but not too much).
FREEZE-DRYING is also a process where moisture is removed from the foods/ingredients, but in this case the initial ingredient is frozen. In case of freeze dried meat treats in our shop, the meat is frozen raw. The process of removing moisture from the food is called “sublimation”, which means that ice is directly transformed into vapour. Since the initial ingredient is frozen, the finished product keeps its original shape.
Neither process cooks the raw product, so both retain nutritional value. Freeze-dried products are often considered the closest to fresh foods, since they retain most of its nutritional value. The heat applied throughout air-drying may break down certain nutritional elements, but it preserves many as well (definitely more than baked, cooked or other preservation processes).
The final results vary greatly on the type of food (meat, fish, fruit, vegetables, herbs, etc.), its shape and the ripeness, water content, colour, etc.
Generally, these are the (very minor) differences:
- Colour: usually the air-dried final product has more intense colour, due to higher amount of moisture; freeze-dried fruits are slightly paler, but still intense.
- Smell: in terms of meat and fish, freeze-dried final product has a mild and more pleasant smell, while air dried meat and fish can have a more intense smell (though be mindful of super stinky airdried treats, this might mean that their quality is not the best!)
- Flavour: freeze-dried final products have a more intense and concentrated flavour (and are therefore a preferred choice of my dogs). This doesn´t mean that air dried finished product is not flavourful, but when comparing the two, my dogs will always choose freeze-dried.
- Texture: freeze-dried final products are usually more crunchier and brittle, while air-dried are more dense and don´t really break easily (due to higher water content).
- Weight: freeze-dried final product is very light, much lighter than air dried (due to higher amount of moisture that was removed). In some cases, freeze-dried products can break easily, especially in case of fruits.
- Moisture: as mentioned before, both processes remove water from the ingredients, but freeze-drying removes more of the moisture. This is why the freeze-dried final products are dry, without any grease or residue. In case of fruits, especially blueberries and raspberries, they might leave a trace of colourful dust on your hands and make them blue/pink.
- Option to rehydrate: Because cell structure remains intact throughout the freeze-drying process, those cells remain ready to take on water again. Freeze-dried products may rehydrate in a couple minutes, whereas air-dried products may take closer to thirty minutes – once again depending on the specific product.
- Nutritional value: as mentioned before, freeze-dried final product is the closest to the original ingredient. No process is perfect, so we cannot claim that the nutritional value is exactly the same, but compared to air-dried finished product, freeze-dried contain more nutrients and less moisture (which is why, on the other hand, you need to always have water available for your dog!).
- Shelf life: this is directly connected to the amount of moisture that has been removed from the initial ingredient. Removing water removes potential for bacterial growth. Since air-dried products contain more moisture, they have a shorter shelf life. Actual length of shelf life for any given freeze-dried or air-dried product depends on packaging, storage temperature and the product itself.
Generally, there is a simple rule: with good ingredients, you will get a quality final product. The process itself is not as important as the initial ingredient, its quality and nutritional value. So be mindful of that, when you are buying treats or food for your dog and/or cat!
You can find a variety of different types, shapes and flavours of freeze-dried and air-dried treats for dogs (and cats) in our shop: www.lyodog.com/shop
