Last Saturday I got around to doing one of those long overdue jobs in the house – defrosting and clearing out the freezer. There are numerous reasons why this was a good idea – it’s not just about getting rid of the food that has been there rather too long, but also about making sure it works properly.
There was probably about a centimetre’s worth of ice over the walls and ceiling (it’s an upright freezer – below the fridge) – thicker in patches. I collected 2 kilograms of it – (I weighed it) – and maybe another kilogram ended up lost in puddles across the floor. Now, for a start, that’s three litres of space that couldn’t be used for storing stuff that now has been recovered. But more significantly, it’s going to make the freezer rather more efficient.
Ice isn’t a particularly great conductor of heat. That means to remove the heat from the inside of the freezer, the pump has to work a bit harder, because there is a natural layer of insulation (the ice) around the food. Ice in a freezer isn’t a sign of a cold freezer – it’s probably a sign of one that isn’t cold enough. That’s also why a snowhole can save you if you are caught out on a mountain in bad weather – the snow contains lots of air and quite a good insulator – plus you also get yourself out of the wind. A cold place, yes, but not one that will suck heat from you terribly quickly.
The ice comes from the air. Warm air carries water vapour (it certainly does in damp Waikato). When you open your freezer door, the damp air hits the cold surfaces, cools down, and releases its moisture. This deposits as ice crystals. Try leaving the door of your freezer open with it switched on, and see what happens. I did this accidently once and the result (after I got back from holiday) was pretty impressive. It didn’t do the food much good though.
Now, with a nice clean freezer, and the door firmly closed, we shouldn’t have any trouble with our ice cream.