Swell-drying - DIC drying and texturing

Fruits and vegetables, cereals and seeds, plants and algae, mushrooms and roots, ingredients and spices... intended for food, pharmaceutical or cosmetic consumption, often require a preservation operation prior to use, enabling storage, transport and facilitating processing. However, agricultural production throughout the world suffers losses of over 40%, mainly due to the absence of appropriate preservation operations capable of taking into account the specific requirements of the products and the specific infrastructure of the production areas. Although simple, freezing and appertizing operations are not easily accessible to farmers, are difficult to apply in the harvesting area, and are economically penalizing in terms of transport.

On the other hand, traditional hot-air drying stands out for its ease of application, its suitability for a wide range of products, and the fact that it can be used directly by the farmer close to the production area. Solar drying also offers the advantage of a considerable reduction in the normally high cost of energy. However, poor organoleptic and nutritional quality, hygiene problems and difficulties in further processing (grinding, rehydration...) prevent the appropriate adoption of this process and the finished product.

Other drying processes (freeze-drying, superheated steam, microwaves, etc.) have been aimed at improving quality, but have failed to meet the need for perfect microbiological decontamination and low final cost.

The poor quality of hot-air-dried products is often due to their low drying speed, with the result that their texture becomes even more compact as a result of shrinkage. As long as the product has not yet undergone glass transition, the body loses water and collapses under its own weight.

Texturing operations were then proposed to intensify conventional drying, and improve the quality of the dried product. Swell-drying" was thus defined as a combination of hot-air drying and controlled instant expansion (CIE) texturing. CID enables a wide range of products to be processed, despite their possible thermal fragility, considerably improving drying speed and product quality. As a result, the finished product has a higher vitamin content than conventionally dried products, without reaching the level of a freeze-dried product. However, CID does enable color preservation, flavonoid availability and antioxidant activity to be considerably higher than with the raw material. What's more, thanks to extensive microbiological decontamination and complete disinsectisation, DIC ensures a much longer shelf-life.