The fast freeze facility on a freezer is basically a button you press which lowers the temperature of the freezer or a part of it. It bypasses the thermostat control and stays that way until you cancel it.
Research has shown that whereas 95% of fridge-freezer owners value highly a frost free feature, only 7% value a fast freeze feature.
Even when owners have a fast freeze feature on their fridge freezer, the vast mmajoroty do not even know it exists.
This facility is used when you need to freeze larger amounts of fresh, unfrozen food. The faster that food is frozen, the better the quality will be when the food is thawed.
Most freezers can cope quite well with freezing small amounts of food without a fast freeze button. Anything over 1 kg (2.2lb) though will result in poorer quality food. We recommend that you turn on the fast freeze function about three hours before placing the food in the freezer.
Fresh food that is frozen at a normal rate will have larger ice crystals in it when compared to food that is fast frozen. The larger the ice crystals, the poorer the quality of the food when it is thawed. If you only plan to store pre-frozen food then you don't need a fast freeze button.
Most freezers with a fast freeze button also have a warning light to indicate that the fast freeze is on. This is useful to remind you to turn it off when the food is fully frozen.
What the light doesn't tell you is when to turn the fast freeze off. You need to have some idea about this time because leaving the fast freeze button on for too long is a waste of energy.
There is no research on this subject which we can find. Possibly because the answer is very dependent on the amount of food being placed in the fridge freezer on fast freeze. The larger the volume of the food, the longer it will take to freeze. We would suggest that turning the fast freeze feature off six hours after placing the food in the freezer would cover most situations.
The fast freeze button is a convenience rather than a necessity. It is quite possible to manually lower the temperature to the minimum possible using the thermostat. Make sure though that it is in a convenient position if you plan to adjust it frequently.
A freezer magnet can be placed on the front of the freezer to remind you to turn the thermostat up to normal when the food is frozen. The correct temperature for fast freezing in a domestic freezer is about -10°F (-23°C).