Tips from Martha: Preheating the Oven (Part 2 of 2)

As I read through Martha Stewart’s Baking Handbook I’m picking up pearls of baking wisdom. But many of the recommendations and To Do’s don’t have a lot of the “Why” behind them. In these “Tips from Martha” I further investigate the deeper reasoning.

Last week, we discussed the argument that preheating the oven is a waste of energy. Today, we look at why one would need to preheat the oven for 20-30 minutes as recommended by Martha Stewart in this cookbook.

Here’s some insight into any cookbook’s guidance to preheat: Since all ovens aren’t the same (an axiom that covers the differences in oven temperatures between say gas and electric ovens or ovens by different manufacturers), cookbook authors must come up with some instruction that will get the majority of at-home cooks to the same end result.

It’s like the scientific method from 7th grade: you have to create a duplicable experiment! If the authors said, “Don’t preheat the oven” they wouldn’t then be able to follow through with reliable cook times, not knowing how long it would take anyone’s oven to get to the right temp.

SO! Part A: Cookbooks must tell you to preheat the oven so that everyone is starting from the same temperature and thus can fully follow the subsequent directions. Therefore, no matter whether or not you think preheating the oven wastes energy, it doesn’t matter: the cookbook author must advise to preheat.

BUT! Back to the deeper question at hand about preheating for 20-30 minutes. Cookbook author Dorie Greenspan explains:

“Mr. RepairMan [who was there to fix her oven] explained that ovens cycle on and off to maintain an average temperature…And that some ovens cycle further up and down from the desired temperature than others. And that some cycle more frequently than others.

“Mr. RepairMan said that when the oven light goes off for the first time, the oven is hotter than the temperature it’s set to.  For example, he explained that my oven swings plus/minus about 25 degrees F.  [And], if I set it for 350F…when it first preheats, it’ll go as high as 400F.  According to Mr. RepairMan, the oven hits its stride and keeps the most consistent temperature after it has cycled on and off three times.”

Ah ha! So there you go! Preheating the oven for a longer period of time gives the oven more time to heat to the correct temperature without crazy temperature swings. My math brain would like to illustrate with this simple graph:

Preheating Oven
Graph of when the oven temperature normalizes to desired temperature. Fabricated numbers for illustrative purposes only.

At this point your cookbook author is more confident that the directions that follow about baking time will lead you, Dear Home Cook, to a more reliable and delicious outcome.

All this leads me to conclude that it makes sense for Martha to tell us to preheat the oven for 20-30 minutes to ensure that we are on the same page temperature-wise before moving forward and thus can expect the best outcome, all else equal.

I would say this though: If you get to know your oven well (probably by employing an oven thermometer), you may discover that you can cut your preheat time or not preheat at all if you work out how much longer you may need to bake to make up that time.

Isn’t math fun!? Further thoughts?

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4 thoughts on “Tips from Martha: Preheating the Oven (Part 2 of 2)

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