The purpose of this experiment was to calculate the water content of the food sample. This was done through freeze-drying and comparing wet and dry weights of the sample.
Bench top Freeze Dryer
(pharmaceuticalonline.com)
Water Phase Diagram
(socratic.org)
Methods
To start the freeze-drying process, it is first necessary to freeze the raw material at a temperature of -18°C (-0.4°F)
The second step of the process is the extraction of the water from the raw material. The product is placed in a vacuum chamber. Under very low pressure, the frozen water contained in its structure is removed in the form of steam. This is called sublimation. To create sublimation, energy in the form of heat is needed. This energy can either be gained from the temperature difference between chamber and product or be supplied by built in heating systems. Freeze-drying starts to be possible at a temperature of 35°C (95°F).
After the free ice has been removed by sublimation, the product still contains bound water which could affect shelf life and quality. During post-drying the most strongly bound water inside the product is converted into steam. This is a slow process. Post drying is called the third step, but begins during the main drying.
A crushed wet weight was taken prior to Freeze Drying, and a dry weight was taken after.