Freeze-drying and its application to some Finnish agricultural products

Abstract

This study deals with the freeze-drying of berries, vegetables, roots and pork produced in Finland. The products were freeze dried whole, in slices or cubes. The pressure in the drying chamber was 10—20 Pa and the maximum surface temperature +23—+ 40°C. The products were packed after freeze-drying into glass jars under air and in polyester-aluminium-polyethene foil under vacuum or nitrogen atmosphere. The drying temperatures and drying times were measured. During storage for 4 months, the differences in quality were evaluated. The drying times ranged from 8 to 25 hours. The moisture content of the dry products was 1—3 %. The sublimation rate at the beginning of the drying process was very rapid, being there after constant. Bilberries, carrots and radishes collapsed during drying. Most of the products dried moistened and underwent aroma changes during storage in glass jars under air. The products packed under vacuum or nitrogen atmosphere proved stable.