How hot is your oven?


Oven thermometerSeems like a silly question: the answer would be it’s as hot as I set it to be. Isn’t it? Well, no, it may actually be rather different from what you expect, based on my recent tests.

I was reading on several bread-baking forums about oven temperatures and the effects on baking. Specifically on the crust: higher temperatures (450F and up) lead to crunchy crusts as the sugars caramelize rapidly. Then there’s “non-enzymatic browning:” the Maillard reaction that happens at a range of temperatures:

The reactive carbonyl group of the sugar reacts with the nucleophilic amino group of the amino acid, and forms a complex mixture of poorly characterized molecules responsible for a range of odors and flavors… In the process, hundreds of different flavor compounds are created. These compounds, in turn, break down to form yet more new flavor compounds, and so on. Each type of food has a very distinctive set of flavor compounds that are formed during the Maillard reaction. It is these same compounds flavor scientists have used over the years to make reaction flavors.

The Maillard reaction is what makes bread become toast. Caramelization is different, as Wikipedia also tells us:

Caramelization is an entirely different process from Maillard browning, though the results of the two processes are sometimes similar to the naked eye (and tastebuds). Caramelization may sometimes cause browning in the same foods in which the Maillard reaction occurs, but the two processes are distinct. They both are promoted by heating, but the Maillard reaction involves amino acids… whereas caramelization is simply the pyrolysis of certain sugars.

The following things are a result of the Maillard browning reaction:
Caramel made from milk and sugar, especially in candies: Milk is high in protein (amino acids), and browning of food involving this complex ingredient would most likely include Maillard reactions.
Chocolate and maple syrup
Lightly roasted peanuts

When cooking, the Maillard reaction can be achieved at lower temperatures (for example, when using the sous-vide method or when searing meats) by increasing the pH of the item being cooked. The most common method for accomplishing this is by using baking soda as a catalyst to facilitate the reaction.

Some complex chemistry going on there (which is one of the reasons bread making intrigues me: it’s science in the kitchen!).

Whole wheat loafThe Modernist Cuisine site has a good explanation of the process:

The Maillard reaction occurs in cooking of almost all kinds of foods, although the simple sugars and amino acids present produce distinctly different aromas. This is why baking bread doesn’t smell like roasting meat or frying fish, even though all these foods depend on Maillard reactions for flavor. The Maillard reaction, or its absence, distinguishes the flavors of boiled, poached, or steamed foods from the flavors of the same foods that have been grilled, roasted, or otherwise cooked at temperatures high enough to dehydrate the surface rapidly; in other words, at temperatures above the boiling point of water. These two factors, dryness and temperature, are the key controls for the rate of the Maillard reaction.

High-temperature cooking speeds up the Maillard reaction because heat both increases the rate of chemical reactions and accelerates the evaporation of water. As the food dries, the concentration of reactant compounds increases and the temperature climbs more rapidly.

Thought Cannon adds some interesting notes, with some ideas on how to make the Maillard reaction work for you when cooking:

So you see what I mean here; the Maillard reaction is all around you. People sometimes confuse caremelization for the Maillard reaction. That’s what the Japanese would call a dickmuva, and here’s why:
If caramelization was the only thing that made things turn brown then you’d be telling me the grill marks on a porterhouse steak are from all the sugar inside the beef. Obviously the beef isn’t full of sugar (though there is a minor interplay of sugars with Maillard). Caramelization happens with sugars, the Maillard Reaction happens with proteins.
With foods like mushrooms and deeply roasted coffees, you are getting both caramelization AND maillard reactions which is ideal. Each one produces myriad different flavors and aromas, so you want them to join forces in the fight for tastiness.

With bread, both processes are at work. How this affects flavour and crust in bread is explained in this baking newsletter:

Crust coloring during baking results from caramelization of sugars, and from the Maillard reactions between reducing sugars and amino acids. Both require heat and are nonenzymatic, but Maillard reactions require less heat and are especially interesting because of the large number of end products that result from a small number of reactants.

It also contains a good article on how the ingredients affect the flavours of bread.

Two components of baking you can control are time and temperature. As it says on The Fresh Loaf about temperature:

Temperature also has an impact on how your loaf bakes. The general rule is that crusty breads should be baked at as high a temperature as possible. Soft shelled breads should be baked at lower temperatures. When you increase the temperature of your oven your bread bakes quicker (duh).

Professional bakers of rustic breads use ovens that achieve higher temperatures than home ovens achieve. Turning the temperature of your oven up when baking rustic breads will help you get closer to professional quality loaves. Buying a pizza or baking stone is another inexpensive method of capturing more heat in your oven and improving the quality of your bread…

Better Homes and Gardens tells us:

If the oven is too hot or too cool when the bread goes in, you’ll end up with a dense loaf. To avoid errors, preheat your oven to the temperature given in your recipe. Use an oven thermometer to make sure your oven temperature is accurate. If needed, adjust the temperature until it’s correct.

I found a reprint of a 1920s-30s’ guide for baking bread online that expressed some of the same concerns bakers have today, almost a century later, in considerable detail:

In baking bread, it is necessary first to provide the oven with heat of the right temperature and of sufficient strength to last throughout the baking. As is indicated in Figure 4, the usual oven temperature for successful bread baking is from 380 to 425 degrees Fahrenheit, but in both the first and the last part of the baking the heat should be less than during the middle of it. An oven thermometer or an oven gauge is a very good means of determining the temperature of the oven. But if neither of these is available the heat may be tested by placing in the oven a white cracker, a piece of white paper, or a layer of flour spread on a shallow tin pan. If any one of these becomes a light brown in 5 minutes, the oven is right to commence baking. Every precaution should be taken to have the oven just right at first, for if the bread is placed in an oven that is too hot the yeast plant will be killed immediately and the rising consequently checked. Of course, the bread will rise to some extent even if the yeast plant is killed at once, for the carbon dioxide that the dough contains will expand as it becomes heated and will force the loaf up; but bread baked in this way is generally very unsatisfactory, because a hard crust forms on the top and it must either burst or retard the rising of the loaf. If the heat is not sufficient, the dough will continue to rise until the air cells run together and cause large holes to form in the loaf. In an oven that is just moderately hot, or has a temperature of about 400 degrees, the yeast plant will not be killed so quickly, the dough will continue to rise for some time, and the crust of the bread should begin to brown in about 15 minutes.

At lower temperatures (325-350F), bread develops a softer crust; the sort of crust most people expect on sandwich bread and dinner rolls. Also, the crumbs form differently in both; generally the spongy sandwich bread is baked at lower temperatures, while the aerated artisan, ciabatta and batards are baked at higher temperatures.

Backwoods Homes give some tips:

How can a home oven be kept hot, even when the door must be opened? One simple trick is to preheat the oven too high. For example, a basic loaf made with flour, water, yeast, and salt bakes at a temperature of 450° F. Preheat the oven to 500°. Put the dough in as quickly as possible, shut the door, and turn the temperature down to 450°. The oven temperature will have dropped, but it will be closer to 450° than it would have been without the extra preheating.

Another solution is to bake bread on a pizza stone. The stone must be preheated with the oven. Introducing a cold stone with the dough would exacerbate the problem of lost oven heat. When the dough is placed on the stone and the oven door is shut, the stone radiates heat, reheating the small oven and providing heat to the dough. Extra stones in the oven can increase this effect. Some bakers place a second pizza stone on the rack over the baking rack so that heat radiates down from above the dough. If you plan to line your whole oven with stones, make sure to leave space at the sides so that heat can circulate.

A second stone above the first? Hadn’t thought about that. How to convince Susan we need another one…? Or maybe I could use a slice of granite…

I have a fairly new, GE Profile gas stove, with digital/electronic controls that beeps when it reaches the set heat. I expected it to be fairly accurate. However, I was surprised when I ran some tests using an oven thermometer (shown above) I purchased online (I looked, but was unable to find one locally).

(It also has a convection fan, which allows for some interesting cooking results, but I’ll get to that anon.)

Ovens have thermal planes, it appears. The temperature of the lower and upper regions in a small home oven may vary by as much as 25F, according to my tests (higher temperatures at the top, as heat rises). That means the location of the built-in thermometer is crucial for establishing a base heat. I believe my stove’s thermometer is at the top, so I placed the test thermometer near the bottom.

I also discovered there is a difference between front and back – possibly some air transfer at the front, or it could be a loss of heat at the front when the door is opened, while the back retains more of its heat. Slate Magazine has a good article about the difficulty of trying to control oven temperatures:

You’d be forgiven for thinking that 350 on the dial means 350 in the oven. You’d be wrong, though. When you set an oven to 350 degrees, there isn’t a single spot inside of it that stays at 350 degrees for the duration of a bake session. The modern gas or electric oven has an automatic thermostat that, by design, lets the temperature drop a predetermined number of degrees below your chosen temperature before switching the heat on. The heat then surges the oven well past the desired temperature before shutting off again. A 350-degree residential oven is designed to stay between around 330 and 370 degrees—and that’s if it’s well-calibrated, which few ovens are. And that’s just at the location of the internal thermostat—the rest of the oven is a different story. Every oven has hot and cool spots so difficult to predict that oven design has become something of a mystical pursuit.

Sandwich loaf, Dec 21I found it took about ten minutes at 200F before the lower region consistently showed 200F on my thermometer, although the stove’s readout said it was at 200. That was (to me) a surprising amount of time for a small space. I will have to experiment a bit with the convection fan to see if I can speed that up.

At 450F, it took about 15-20 minutes for the oven to equalize. It was a bit faster when I set the temperature for 475F for 10 minutes, then reduced it. That gave me what appeared to be an even 450F top and bottom.

One of my issues has been less-than-desired cooking of the dough at the bottom of some loaves. I now suspect it’s because the oven  wasn’t fully at the set heat yet (and I put the dough in too soon), or there was a difference between the temperatures at the top and bottom of the loaf. That didn’t happen with my latest loaf (pictured left), when the oven was pre-heated.

I have already read that heating a baking stone or a Dutch oven (iron pot) to the proper temperature for baking requires pre-heating for 30-60 minutes. Lesson learned: pre-heat; don’t just put the dough into the oven when the stove beeps.

However, either the heat was higher at the back or the oven walls retained more of the higher heat than expected (radiating it unevenly). The back of my most recent loaf’s top (baked Dec 21) was somewhat crispier and browner than the front (not enough to make it unpleasant, but noticeably different to the eye and mouth feel). Given the recent loaf was intended as a sandwich bread, I might have done better to bake it at a lower temperature, but the recipe called for 450F.*

I have to consider either rotating the bread mid-way during the baking cycle (somewhat chancy, since opening the door lets out heat, which itself may affect the results), or  perhaps changing/lowering the location of the rack (this was a pan loaf on a rack, not baked on the stone).

This also leads me to convection baking. Convection can produce very good results; because the air circulates better, it can do a more even job of baking. When set to convection baking, the stove compensates by dropping the temperature 25F. I will have to test whether the temperature range when using convection is as large as without. I also find it works best to pre-heat the oven on non-convection mode, then when it’s hot, switch to convection, but this is based on some preliminary experiments, and isn’t conclusive.

More research is required. And that’s part of the fun of baking bread.

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PS. Maybe my tastes have changed since I started baking my own bread, but I was severely disappointed recently when I purchased some “sourdough baguettes” from a local grocery store to use with a cheese fondue this weekend.  I didn’t have any suitable homemade bread in the necessary quantity, so we bought what we thought would be appropriate. It was doughy – perhaps somewhat undercooked – and rather tasteless, at least compared to other commercial sourdoughs I’ve had. We were modestly compensated for the mediocre bread by the pleasant  taste of our homemade wine – an old-vine Zinfandel that turned out to be an excellent product when paired with the cheese.

* Another topic I want to tackle is the use of salt in bread recipes. Most call for 2-2.5% salt, which seems to me somewhat high. We don’t cook with salt or use it any foods aside from bread, so it might be my tastebuds are acclimatized to lower amounts. I find using the called-for amounts makes the bread too salty. This last loaf called for 10g, which I reduced to 6. But salt is more than for taste: it’s a yeast inhibitor, so too small an amount may be problematic, too. More on that in a future post, when I’ve done a few more tests.