Freeze Drying basic
The product to be freeze dried must be present in a deep frozen form. The freeze drying takes place under vacuum conditions below the "triple point" (6.2 mbar = 4.6 torr). Here water will only be present in two phases: ice and vapour. By adding energy to the ice it will sublimate (evaporate) directly into the vapour phase. The vapour is condensed immediately on vapour traps to maintain the vacuum.
Water vapour has easier access through any product cel structure compared to water penetrating the product mass to evaporate from the surface from the product as in the case in after drying methods. The gentle escape of water vapour in the freeze drying process leaves the product close to its original shape, and its taste and colour is preserved and there is no loss of aroma.
The vacuum and temperature used during the freeze drying operation depends on the product, its shape, water content, product structure and composition.
Preparation of the products
Products for freeze drying falls into three basic categories:
- Liquids such as coffee and tea, juices and other extracts
- Individual quick frozen (IQF) product. Such a segment of or whole fruits, berries and vegetables as well as for instance shrimps or segments of fish and meat products.
- Combined products such as soup blochs, rice, dishes, baby purees, camping foods etc.
Freeze drying of liquids is the most complex. First the liquids must be treated to achieve the optimal solids content and colour. The preconcenttrated liquids must be frozen before the freeze drying. This is done either slowly on a CAB (Concentrated Air Blast) freezer or mor quickly on ROTA freezer. The frozen product is then granulated (milled) to obtain granules of the desired size before loading and weighing on trays before the freeze drying. The IQF products are loaded in frozen form directly by weight or volume on the trays before the freeze drying.
Combined products are normally filled into trays with special plastic moulds that can withstand the extreme temperature changes. The product is then deep frozen in the moulds before freeze drying.
World leading supplier of freeze dryer systems
GEA Niro is the world leading supplier of Atlas freeze dryer system and equipment utilized by the coffee and food industry. GEA Niro designs and delivers complete drying plants for the coffee industry, and the leading coffee brands are produced on GEA Niro equipment.
Freeze drying is a superior preservation method for a variety of food products and food ingredients. Atlas freeze dryers set world standards for design, operation and quality. The delivery programme includes plant sizes ranging from pilot scale to large industrial batches and continuous plants.
GEA Niro delivers five types of freeze dryers:
- RAY™ batch plant
- RAY™ S batch plant
- CONRAD™ continuous freeze drying plant
- Pilot RAY™ 1 batch plant
- RAYCON™ for the pharma industry