School physics

A reminder that having done physics at school may not help much with sorting out what might sound like schoolboy physics.

As readers may recall, I have been baking bread for several years now and have reached the 229th batch without succeeding in making white bread - but I can do brown bread, This brown bread is perfectly satisfactory but I do sometimes look at articles about bread baking in the papers, there being quite a lot of them these days. Great bake off on the telly or some such. Several of them have mentioned how much better it is if one puts a tray of water in the bottom of the oven while baking the bread. One even told of steam injection in the ovens of commercial bakers.

Enter the physics. At normal pressure, water boils at 100C, so if one puts a bowl of water in the bottom of an oven which is supposed to be something more than 200C, does one get an explosive boiling, with hot water being blown all over the inside of the oven, possibly triggering some kind of electrical failure? Does all this steam at 100C drain all the heat out of the oven as it is vented?

All of which left me a little nervous, but yesterday I decided to give it a try and put a large pyrex bowl with a couple of inches of cold water in it, maybe a couple of pints, in the bottom of the oven. But the oven did not then come to heat after 20 minutes when it usually takes 10. So I give up at this point, take the near boiling water out, the oven almost immediately comes to heat and I can get on with baking the bread which, as it happened, turned out very well.

BH's contribution was that I was using far too much water. Of course it would take a long time to heat up that amount of water. But she also said that when she did such things - the proper term being a bain-marie (the BBC web site knows all about such things if you don't. It is not just about the BB bit of BBC) - it was for lower temperature cooking, she did boil the water in the kettle first and yes, the bowl was empty at the end. The water all boiled off, or at least evaporated off.

But I continue to wonder about the water boiling at 100C. While the oven door has rubber seals, I am reasonably sure that the oven is vented and is at normal atmospheric pressure. It is not a pressure cooker or a steam engine with an enclosed boiler. So this being so, how can the steam from the water get to be much more than 100C?

Maybe the next step is to try again with much less water in a steel bowl rather than a pyrex bowl, this last being quite a good absorber of heat itself.