Recipes instruct us to preheat our ovens even though it's unnecessary and a waste of energy. Why is this still happening – and when is it actually necessary?
I know this goes against what your mother told you - and contradicts almost every recipe you've ever read: but 99% of the time you don't need to preheat your oven.
This advice, which may come as a shock, works for all modern ovens – fan, electric and gas. (Not, alas, Agas.) Roasts, cakes, bread, cookies, pastry, casseroles and ready meals can successfully and safely be cooked from cold. Every time you use the oven, you can save yourself ten to 20 minutes of preheating; often much longer, as recipes usually tell us to switch on the oven far too soon - the moment we step into the kitchen.
Perhaps the most surprising thing that can be cooked from cold – indeed, it's better - is bread. Elaine Boddy, author of The Sourdough Whisperer, has been recommending this method for years. She places dough in a covered cast iron or enamel pot, then puts that in a cold oven and switches on. 'I receive so many messages from people incredulous that it will work,' she says. 'But then they try it, bake perfect loaves and wonder why they ever bothered wasting time and money preheating.'
One Sunday morning a few months ago, irritated by a legion of gainsayers, I got up early and made a real-time video of Yorkshire pudding batter being poured into a cold tin and started in a cold oven; thirty minutes later, it emerged in a puff of golden glory. Facebook loved it – except for the denizens of Yorkshire. One told me my oven needed cleaning, another accused me of faking it, like the moon landings.
So how does it work? You put the food in the cold oven, and as it heats up, so does the food. It starts to cook at a lower heat than otherwise, but rapidly catches up. Depending on your oven, add six to eight minutes to the stated cooking time. It's really that simple. Any exceptions? The only one I've come across (so far) is home-made pizza, which is a bit of a flop anyway made in a domestic oven.
As always, check food is properly cooked; good recipes give 'indications' as well as timings, so use experience and judgement to determine when it's done. (If I think there will be a next time, I make a note on the recipe of how long it took from cold.)
The mathematically-minded cook may say that if you add time at the end, it cancels the time saved at the beginning; but the total oven time is shorter, and that is how you are saving energy.
I've discovered that some people flatly refuse to believe me. If that's you – maybe you also like cutting up ten-pound notes and throwing them out the window - at least preheat for the minimum time necessary. My fan oven takes 8 minutes to reach 180C, my conventional oven 14 minutes to reach 200C, my friend's gas oven 15 minutes to reach gas 6.
What's puzzling is why this myth has persisted so long. In olden days, of course, cooking appliances were slow and cranky, and it was part of life's daily struggle to get the oven up to heat. By the 1980s and 90s, however, fan ovens were becoming popular; manufacturers assured us that they didn't need preheating, but no one believed them and they have largely given up telling us.
Ask a recipe writer about preheating and they'll tell you that cooks expect accurate timings, and the only way to achieve this is by preheating: the 'level playing field' argument. Food technicians who calculate heating/cooking instructions on prepared foods and ready meals are in the same boat: they want to leave as little leeway as possible for customers to poison themselves. My advice: ignore them, and use your common sense.
By the way, you can save a bit more energy by switching off the oven five to ten minutes before time's up, and letting food finish cooking in residual heat. According to chefspick.co.uk, the average electric oven costs just over 71p per hour to run, so savings add up.