Effect of Freezing Rate on the Quality of Freeze Dried Berries and Vegetables at Institut for Fødevarevidenskab - Københavns Universitet


Freeze drying is used for preservation of food due to its gentle processing and specific quality attributes attainable compared to other drying methods. Specifically, the preservation of nutrients, vitamins, flavour and colour, as well as the development of the characteristic brittle texture.

The standard freezing method for berries and vegetables, as a pre-processing step prior to freeze drying, is air blast freezing, providing a medium-fast freezing rate. Several other freezing methods are available to the industry, such as natural convection freezing or freezing by submerging in liquid nitrogen. These methods provide radically different freezing rates.

The effect of different freezing rates on quality attributes, as well as drying rates, have been investigated for liquid products, such as concentrated coffee extract and pharmaceutical formulations, but has yet to be investigated for solid foods such as berries, fruits and vegetables.

The idea of this project is to investigate the effect of freezing rate of berries and vegetables on quality attributes of the freeze dried product. The processing is to be carried out at the GEA Test Centre located in Søborg, using different industrial freezing methods in pilot scale and small-scale freeze dryer.

A primary indication of the differences in the freezing structure could be differences in time to execute the freeze drying process (sublimation rate), which might be caused by differences in ice crystal morphology. Analytical work would be expected to cover dry matter, shrinkage, colour change, physical strength of the dry product, scanning electronic microscopy investigation as well as others. Some to be carried out at KU, some at GEA.

Ideally, the time frame of the project would be set to enable the use of fresh berries sourced locally in Denmark (meaning August/September). Products used as case study could be raspberries, cubed carrots and others.

Contact persons / supervisors:

Karsten Olsen, Associate Professor, Design and Consumer Behavior (ko@food.ku.dk)
Jens Risbo, Associate Professor, Ingredient and Dairy Technology (jri@food.ku.dk)
Troels B. Pedersen, Process Technologist, GEA Process Engineering A/S (Troels.Pedersen@gea.com)

Attention: When applying for this thesis, remember that there are specific regulations and requirements that needs to be met in order for you to include it as part of your education. For more information on criteria, please contact your local student advisor as outlined here Faculty student advisors (in Danish)

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