Excerpt from the test report LVA
Development of a high quality
Drying process for food
(Summary of the test report of the LVA - Austrian Food Research Institute)
November 9, 2018
Various parameters were tested for the drying of fine-fiber to coarse-fiber plants and plant parts. As experimental products, e.g. Herbs, cut fruit and minced vegetables, berries in the whole, mushroom pieces and flowers for use.
The very gentle water extraction process allows the production of premium quality products and, associated with that, higher added value.
As part of process development, the technological principle of water extraction is used. The air is dried in a closed body by a dehydration process, and the dry air is passed over the dry matter. By circulating the air and maintaining a cycle with intervals of less and more strained air, a quality of the material to be dried is achieved which is similar to that of freeze-dried products.
The material to be dried is pushed onto food-safe plastic trays with perforated trays on the rail guide into the drying cabinet and remains there until the desired quality is achieved (breakage test). A precise removal is not necessary - there is no risk of over-drying.
Particularly noteworthy is the short drying time. The short process time favors the preservation of ingredients that are affected by conventional drying processes.
For the quality issues concerning the product, optimal process parameters were tested, the final products were tested by sensors and analytics, the product safety was evaluated and the shelf life was estimated.
The drying process itself was observed in terms of temperature / humidity history and outlined an implementation concept for the adaptation of alternative products.
As a rule, a foodstuff is stable on storage if the aw value does not exceed the limit of 0.7. Low aw values indicate high resistance to microbial attack and spoilage. The samples of food from the oven were examined and data were collected on the aw value range after chemical analysis.
An important measure of the roadworthiness of food is the microbiological safety. In particular, herbs are often heavily contaminated in high numbers of germs. Using classical cultural techniques, general indicators from the product flora were recorded, analyzed and assessed.
Various product samples were presented, evaluated and reconstituted. Analytical tasting under controlled conditions extended laboratory tests to include sensory parameters.
A holistic approach to product and technology evaluation was chosen, highlighting the strong dependence on product quality and process management.
Assessment of the products
It could be confirmed that the original texture of the different foods remained relatively well preserved (the capillaries of the tissue do not collapse). The ingredients that give color and taste, even in the dried product still have an optimal effect.
The food tested for water activity provided assay results ranging from 0.2 to 0.6. As a rule, products in this aw value range can be classified as above average stable.
The results of the laboratory analyzes are summarized here in tabular form
Sample name (aw value)
Aronia 3 days 0.425
Apple slices 0,317
Wild garlic 0,610
The microbiological parameters were thoroughly assessed. Especially herbs and spices are often highly contaminated with germs, because the technological processing inhibits the natural flora, but the manipulations often cause recontamination. The project samples apple slices and wild garlic were in a remarkably good microbiological state with germ counts below 1000 and 11000.
Summary of the technology
The developed water extraction process can be classified as extremely efficient in terms of achieved drying parameters.
Shelf life of the products is considered to be superior to that of conventional dry produce, given the low aw values.
In addition, the preservation of a near-natural texture and rehydratable matrix succeeds.
The dry products with pure fruits and vegetables achieve a high quality of the products and thus a higher value creation in the marketing possible.
Due to the short process time high throughput rates are possible, whereby a high production quantity can be achieved. In view of the longer drying times in the conventional drying could for this variant with the short drying intervals an energy potential can be detected.
The considered drying process goes beyond the usual state of the art in terms of drying rate and achievable product quality. The drying oven can be used to produce stable, storable products with a high quality level (sensory and hygienic).