On the occasion of Jour du Macaron 2010 (I’m a few hours late) and the approximate occasion of Syrup & Tang’s third birthday, I have decided to write about ovens, rather than presenting more pretty domes of deliciousness. Why ovens? Because a lack of understanding of how ovens work is one of the main causes of so many home bakers’ problems. And I promised to write about them a year ago.

Many of you know that the macaron has become one of the, um, signatures of Syrup & Tang. In December 2007, I wrote a series of explanatory articles which I dubbed La Macaronicité. Many, many questions have been answered in the comments to those articles, and my instructions and formulae have been reproduced all over the place (sometimes without acknowledgement, unfortunately).

It’s easy to bring together the themes of ovens and macarons, because if you know your oven, the likelihood of a successful batch of macarons, for instance, is much greater. Knowing your oven is more than just the common problems of people (1) just not letting their ovens preheat for long enough (your oven’s walls need to absorb and then retain heat: it takes more than 15minutes!), and (2) opening oven doors for too long (you can usually expect a drop of at least 10C in a simple open-insert-close transaction).

Please remember that this material is copyright. If you want to use any part of it (beyond a very short quote), please contact me for permission.

Among the many problems macaron-makers face, there are five that are almost always caused by issues with heat:

• no feet
• lopsided feet
• air pockets
• ruptured shell (minor volcano)
• sticky bottoms

Issues which aren’t usually to do with heat are: wet macarons, collapsed or cracked shells, very thin (translucent) shells (some of these issues are discussed in other posts).

Time for macaron-physics 101!

A macaron has an outer shell which should be thin and crisp in its cooked form (not thick and crunchy!). Below this crisp exterior is soft airy cooked batter, and keeping that soft stomach in is a thin dry layer with a chewy edge (the foot) where the macaron was in contact with the baking paper or Silpat. How is it that the sticky, temperamental batter of almond meal, sugar and egg white turns into a dome of three textures?

Heat causes drying, expansion and a whole pile of other more interesting things to happen. Our primary concern is how the distribution of heat in the oven affects the correct development of the shell. The diagram below gives you an idea of the desired process, with a hard shell forming before the air in the batter under shell expands too much. (Ok, other things expand too, but the air is the main thing.) With the right timing, the expanding batter causes the shell to lift, with the foot forming in the gap between shell edge and baking tray.

When reading most macaron recipes, you’ll find (a) no info about the type of oven (fan-forced or no-fan), (b) occasional strong recommendations for using stacked baking trays, (c) various instructions to vent the oven by opening the door at some point during cooking.

None of that helps most bakers.

People obey these instructions without having been given insight into why or how relevant such things are for their own situation. Is your oven gas or electric? Does the heat source cover the bottom of your oven, the rear of the oven, the top of the oven? Fan or no fan? Is your thermostat reliable? How efficiently does your oven recover from the door being opened? I could go on.

When I wrote my first instructions for making macarons in my La Macaronicité series, I had battled through so many wasted batches of these diva-biscuits thanks to my belief that published recipes would help me understand what to do right. Doubling baking trays was utterly wrong for my oven (type B below). Venting the oven was pointless. Leaving the shells for an hour before baking was unnecessary (but at least had little negative effect). It took a while after that for me to better understand the relationship between hardened crust, batter expansion under the shell and the resultant rise of the macaron off the baking surface. I get the feeling that too many people who should know this stuff are nonchalant about communicating it to home bakers.

Of fundamental importance: heat rises. If your heat source is built into the base of the oven (oven image A), as in many modern gas ovens (especially in Europe, perhaps also North America), the heat rises strongly below a baking tray. If the gas flame is at the back of the bottom of the oven (type B), as in typical older Australian oven designs, heat below the tray will be relatively weak. Electric ovens vary in element placement and heat distribution, but if you have a crappy electric oven with an element just at the top (type D), abandon much hope of easy macaron making without a serious oven stone of some sort to store heat in the lower part of the oven.

That double-tray thing you might have read about is entirely a function of people baking with ovens with lots of heat under the trays (types A/C). You double the trays to slow down the penetration of heat from below which could otherwise cause a weak outer shell to burst (minor volcano) and/or the base to brown before the rest of the shell is done. In my case (oven B), I needed to *increase* the heat below the macarons by heating the tray, otherwise the bases were always sticky, making the macarons impossible to remove from the paper.

Please remember that this material is copyright. If you want to use any part of it (beyond a very short quote), please contact me for permission.

Understanding how heat in your oven affects your macarons is at least as important as not overmixing your batter. Doing small test batches of just a few macarons is the easiest, least frustrating way of testing the effects of various parameters (I’ve written that before, both on Syrup & Tang and eGullet, but too many people still chuck a whole tray of macarons in an oven, believing that divine providence will deliver unblemished beauties).

In my original experiments two-and-a-half years ago, I found that air pockets seemed to result from minor temperature differences. In my normal method I almost never experience air pockets, but there are still rare occasions which I can’t explain.

I have to reiterate that home bakers have to be willing to read through tips, comments and to test things out themselves — careful, systematic persistence yields results. The problems that can occur often have multiple interacting causes.

Venting the oven at some point (typically for the last few minutes in a fan-forced oven) helps prevent the shells from browning while letting the bases firm up, but even fan-forced ovens may not be giving truly evenly heat, and there’s the added drying effect of fan-forced cooking.

Leaving the shells to crust (dry on the surface) is a kind of insurance policy. It means the surface hardens in the oven a little more quickly. With lots of heat rising under a single baking tray, the batter can easily erupt through the still-weak crust like a mini-volcano. A harder crust will prevent this and, instead, all that expansion will go towards pushing the shell off the sheet, giving (hopefully) a nice foot. Poor professional bakers often leave their shells to crust for ages, resulting in an overly thick, crunchy shell (hello Sydney and Melbourne!). If you’re unlucky, the uncooked batter can adhere to the baking surface as it crusts, with the result that the shells eventually rise unevenly or the batter vomits out from wherever the seal is weakest.

That’s the round-up of macaron-related oven issues. I hope they help inexperienced home bakers solve problems better with temperamental baked goods like macarons (or canelés or pasteís de nata). I might eventually build this information into the original series of articles, but I don’t have enough time at the moment. If you have observations along the above lines that could strengthen these tips, please share.