Warm and fuzzy
Over the past several months, I've received a number of e-mails from a friend in London who is teaching herself to bake. Very few of her attempts have been successful as she likes to 'fiddle' with recipes: she substitutes whole-grain flour for white plain (all-purpose) flour and reduces the amount of sugar in an attempt to make her produce healthier. I told her to follow the recipes precisely the first time she uses them so she knows what the results are supposed to taste like. I also sent her a few recipes I've made lots of times that simply cannot fail.
Or so I thought.
I finally advised her to buy an oven thermometer, which she did. It turns out the oven's built-in temperature gauge was off by about 30 degrees Celsius, so all the time she thought she was baking at 180 degrees, her food was actually slow-cooking at 150 degrees. No wonder her cakes and muffins were collapsing - she was baking in an oven that wasn't nearly hot enough.
Bread, cakes, tarts and biscuits need to be baked at the correct temperature, or, as my friend discovered, they might not turn out particularly edible. If the oven temperature is correct, it sets the structure of the crumb, gives the baked goods an appetising brown colour and - with breads, anyway - provides the 'oven spring', a final, quick expansion of the gases trapped in the gluten strands of the dough, which makes the finished product lighter. If the temperature is too low, baked goods don't rise sufficiently and become heavy; and they are pale, rather than an appetising brown. If the temperature is too hot, they burn on the outside before the interior is cooked.
It's important to preheat the oven before baking because it makes the product cook more evenly, rather than initially just on the top or bottom (depending on the oven's heat source). If I'm using a small countertop oven, I set the initial temperature higher than I want it, to make up for the heat loss that occurs when the oven door is opened to put the raw dough inside. As a general rule, cakes, tarts and biscuits can be baked at 180 degrees, while bread tends to need a higher temperature (about 220 degrees). If it's a large cake or loaf of bread, you might need to lower the temperature after about 15 minutes, so the interior gets baked through before the outside burns.
When I was baking professionally, I could tell the temperature of the oven quite accurately by putting my arm into it: if I could leave it in there for more than 30 seconds it was too cold to bake in; if it burned me immediately it was too hot. Now my baking is more intermittent, I use a foolproof oven thermometer.