Freeze drying—technically known as lyophilisation, or cryodesiccation is
a dehydration process typically used to preserve a perishable material
or make the material more convenient for transport. A freeze dried fruit
is a dehydrated fruit derived from lyophilisation which can be stored
for longer duration and can be consumed throughout the year.
Process of freeze drying is practically done in three main phases:
• Freezing, or sub-cooling of product below its eutectic point (cca. -30°C and lower);
• Dehydration (drying) by ice sublimation under vacuum; and
• Completion of product drying up to moisture content lower than 3% by the normal
vacuum drying.
Traditionally, freeze-drying is performed at vacuum (vacuum
freeze-drying, VFD), resulting in extensive drying periods with high
operating costs. In order to shorten this period, alternative processes
can be used, such as atmospheric freeze-drying (AFD), where the primary
drying stage (sublimation) occurs at atmospheric pressure. AFD has been
used successfully for drying of berries. Traditional freeze drying
(lyophilisation) is used to quick freeze and vacuum moisture from
a blueberry. This gets the blueberry to a 2 % moisture level where it
is crunchy.
The freeze dry blueberry maintains all of the nutrients of the blueberry
minus the water and an intense blueberry flavor.
According to one study, freeze drying resulted in a higher retention of
total polyphenols and anthocyanins as well as higher antioxidant
activity in the glycoside forms. (International Journal of Food Engineering, Volume 4, Issue 6 July 2008)
Freeze dried blueberries