There are countless advantages to dried fruit and vegetables: they are shelf-stable, portable, lightweight, nutrient dense, and easily added to any recipe. Today we are exploring and comparing these two value-added fruit products and their processes.
Drying fruit and vegetables is a value-added process. Freeze-drying and air-drying add value to fresh fruit and vegetables for the grower and the consumer. These processes enable the food manufacturer and the consumer to use and enjoy the fruit long after it is harvested. Any fruit or vegetable can be dried, but today we will focus on blueberries as an example. Let’s examine these two processes and define some often-misunderstood terminology.
Freeze-drying locks in the nutritional composition and structure of the blueberry through the process of sublimation. Sublimation occurs when frozen water crystals evaporate directly from ice to water vapor under atmospheric change. Processed, IQF (individually quick frozen) free-flow blueberries are used in the freeze-drying process.
This is what happens inside the freeze-drying chamber:
- IQF free-flow blueberries are loaded onto stainless steel trays on carts, which are placed inside the chamber.
- The chamber is sealed and the temperature is lowered until the blueberries reach a preprogrammed subzero temperature. A vacuum lowers the atmospheric pressure until it goes below .06 ATM (measurement of atmospheric pressure).
- Heat is introduced and the ice is vaporized, skipping the liquid phase. The blueberry temperature never rises above 78 degrees F, making them a certified R.A.W. product.
- Within a specific time frame, often 18 to 30 hours, the dry cycle is finished and the chamber is turned off.
- Once the chamber is opened and the carts are rolled out, the fruit or vegetable is allowed to “settle” and then off-loaded into the appropriate packaging.
It is paramount that the packaging protects the resulting blueberries from any moisture. Freeze-dried products are extremely hydroscopic: they take on any available moisture and become chewy very quickly.
This process ensures a long shelf life by removing approximately 98% of the water (more than air-drying) within the blueberry but maintains its shape and color. The unique freezing and then drying technique provides a crunchy treat full of flavor. Think crisp and delicious, not freezer burned.
The air-drying process uses warm air instead of cold atmospheric changes.
This begins with washed and processed blueberries:
- The blueberries are placed on a stainless-steel drying tray in a single layer and fit into a stainless-steel cart that is rolled into a dehydrator tunnel with warm air circulating through it.
- Water activity (Aw) is monitored closely through the process. Aw is important because available moisture left in the blueberries is a perfect medium for microorganism growth and enzyme activity after processing.
- The drying time and air temperature in the tunnel depends on the particular food product being dried.
- Humidity control is very important to the resulting quality in this process. The flavor profile and resulting color of the blueberries is influenced by the percent humidity maintained during the air-drying process.
- When all measurable specifications are met, the carts are removed from the tunnel and the blueberries are allowed to “settle” before being packaged appropriately.
This air-drying process removes approximately 70-80% of the moisture in the blueberries. It does not remove the bound water (the water inside the cell structure) in order to maintain a tasty and delightful eating experience. Removing the bound water can cause the sugar inside the product to become crunchy, often tasting burned and lifeless. This degree of water removal can alter the fruit’s just-picked flavor. Performed correctly, air-drying provides fruit in a shelf-stable form at a lower processing cost than freeze-drying.
End results: what’s the difference?
The major differences between the two processes are moisture content, appearance, and flavor intensity. Freeze-dried fruit retains the fruit’s original shape and becomes crunchy with an intense flavor profile, while air-dried fruit has a higher moisture content and the shape matches the traditional perception of dried fruit. But what are the technical differences?
How to use freeze-dried and air-dried fruit
Both can be eaten as a healthy snack or used in baked goods, salad, oatmeal, or yogurt. These two applications make excellent product ingredients as well and the possibilities are endless. Use them in nutrition bars, trail mix, salad mix, baking mix—anything your R&D team can imagine.
Freeze-dried fruit can be used in most places fresh is used. Just remember freeze-dried fruit takes moisture from whatever it is paired with and will become chewy (but still tasty).
Our main goal is to capture and keep the original “just picked” nutrients in our value-added products while preserving the delicious flavor profiles that each fruit and vegetable brings on their own.
Why we do what we do
We take what we do seriously. The nutritional impact of our crops is important and we pursue value added forms like freeze-dried and air-dried food products for our customers in order to give consumers a variety of delicious ways to include healthy fruit and vegetables in their daily food choices.
If your brand, business, or company wants to incorporate freeze-dried or air-dried fruit into your products, get in touch. Or, if you have further questions about what we do, let us know. We would love to talk.