Stop burning those cookies

I learned a few things baking rocks. I have been trying to understand biscotti — the essential ingredients, the methods, the flavors — but I kept burning their bottoms. So I placed a few rocks in the oven and snooped around with a thermometer to get those cookies to stop burning. Earlier I wrote on what makes an oven work and what to look out for, today I list what I did to get around the limitations of my oven.

1. Insulate the dough

I did two things to protect my dough from the hot coils. First I replaced my baking sheets. My new baking sheets (US$ 3 each, what a bargain) are really two sheets of metal separated by a small gap filled with air. Biscotti baked on these sheets came much closer to my expectations, but there was still a bit too much bottom browning.

Next I placed the cookie dough on a Slipat, one of those oven-safe silicone mats. The mat is a poor heat conductor and also helps keep the dough from sticking to the baking sheet. The Slipat is a great insulator, so if your cookies start coming out undercooked, remember it may be the Slipat. For me, the air gap sheets and the mat provide most of the protection that the cookie bottoms need.

2. Rotate the baking dish

To deal with the temperature differences inside the oven, re-arrange the baking sheets. The back part of the oven is warmer than the front. There are more walls to radiate, no glass door to leak out heat, and better insulation.

Half-way through baking I take out the baking sheet, give it a half turn, and slide it back in. This way each end of the dough gets exposed to the hot part of the oven.

I try to do only one sheet at a time. Most home ovens can only handle one baking sheet full of cookies. If you use two, the lower one is going to get way more heat and at a higher temperature than the upper baking sheet. If you need to have two sheets, swap them when you rotate the sheets: the one that used to be below goes on top.

3. Shield your baking dish

The filaments or flames in the oven are much hotter than the walls of the oven. The areas in the line of sight to those heat source will get more heat at higher temperatures than the rest of the dish. For dishes, such as cookie batters and cakes, where one needs to heat the dish rather than roast it, the direct heat can be avoided by blocking the baking sheet from the direct line of sight of the coils. If you have a gas oven or a modern electric oven, chances are the heat source is already shielded.

In my oven I sometimes use another baking sheet on a rack just below the rack with the cookies. Other times, when I know I will be opening the oven door a lot, I use a baking stone. Place the baking stone in the lowest rack of the oven. Just make sure there is enough space for the air to move around it.

Any unglazed terra-cotta tile or high-temperature glazed tile will serve as a baking stone. I break my tiles often, which I replace with tiles bought for a few dollars from the local building supply store. Before they go in the oven, I put them on the outdoor grille, which gets hotter than the oven and provides a test for the tile. I will not use it if it smokes in the grille.

This is a baking tile I bought from a cooking store to make pizza. I placed this tile in an oven set to 170ºC (340ºF) for an hour and then read the temperature in several spots. The tile got much hotter than the oven setting. Even then, a bit over 200ºC is much less than the 800ºC or so from the coils.

Using a tile or another baking sheet will lower the temperature of the heat radiating on the bottom of your baking sheet.

4. Ovens cook differently

For the same recipe, every oven requires a different temperature and baking time. My times vary from recipe books by as much as 30%. That is not a problem if the recipe calls for 20 minutes and the cookies bake in 25 minutes, but you will have a burnt batch if the cookies were done in 16 minutes. You should use baking times (and even temperatures) only as rough guidelines.

Even if you did the exact same thing as the recipe writer, cooking times would be different. Having exposed heating source in the baking area and the type of vents used by the oven introduce large variations in baking times. My old electric oven has exposed coils, whereas newer models shield the coils. In my childhood home, we had a gas oven with big vents between the flame chamber and the baking area.

These older ovens bake differently than modern home ovens (not necessarily better). Industry uses different types of ovens for different baking tasks. The best oven for making pizza is very different from the best oven for baking a cake.

5. Calibrate your oven

Cookies bake fast and small changes in temperature can take you from baked in 12 minutes, to burnt in 12 minutes. Oven thermometers are inexpensive and give you some control over your recipes. The temperature and timing in a recipe are only guidelines, so when following a recipe for the first time take notes and check often. When you bake the recipe the second time the notes will serve as a guideline. With the same oven (and chef), baking times should be reproducible.

I was surprised to discover that my 22 years old oven’s dial was off by only 25ºF. By loosening two screws in the back of the oven dial it was easy to calibrate the oven.

 

6. Preheating times vary

Ovens warm fast but stones do not. The metal wall of the oven will warm in ten minutes or less (in an electric oven you can tell by the long off period of the element). If you have a baking stone in the oven, the stone may take over an hour to warm up. Once warm, opening the door of the oven to check on the food will let the warm air and vapors out, but the large amount of heat in the stone will help restore the temperature once the door is closed.

7. Not tested

Doughs and breads need water vapor in the initial stages of baking. Ovens exhaust the vapor given out by the dough (gas more than electric), so bread doughs expand less and cakes crack and collapse. Most professional bread baking ovens have a steam injection feature. To reproduce this at home, cookbooks suggest quickly opening the door of the oven and misting some water onto its walls. If you have a stone in the oven the temperature will recover quickly.

Cautions: Be careful with the steam that may come out of the oven. Very hot steam is invisible and will scald. Don’t squirt water directly on flames.

The steam is helpful only in the first few minutes of baking. After that it curtails the dough raise. I have yet to compare a batch made with misting water to a batch made without.

TGRWT 15

Chocolate and smoked salmon in the same dish, that is the challenge for the blogging event TGRWT #15 being hosted by Roberto from Mex Mix. The idea of TGRWT is to create a dish using two ingredients that share aromas. Regularly, Martin from Khymos challenges us with a new combination.

The last time I tried pairing chocolate with something savory was for the TGRWT #5 and I had a really hard time coming up with Koko Kibe. This time I decided to use the chocolate as a condiment and not as a main ingredient. At home we sometimes make a salad of smoked salmon, cucumber, and watercress. To accompany it, I created a chocolate-based dressing. The dressing mixes ingredients that pairwise are eaten together: balsamic vinegar, strawberries, chocolate, and walnuts. The dressing turned out dish-liking good and it went well with the salad. On my scale of A through C (C is edible, B, family will eat, A, can serve to outsiders) it gets an A. The problem with the dish is that the salmon is not as prominent nor as integrated as I would have liked it.

Smoked salmon with chocolate dressing

The smoked salmon, cucumber, and watercress salad has been popular since the 1800s. Charles Senn, a prolific cookbook writer and editor of the London Food and Cookery included Lax à l’huile aux concombres in his 1894 cookbook and instructed us to decorate the dish with watercress.

The watercress could be replaced by another bitter green such as spinach or arugula. For the chocolate I used dark sweet Callebaut (54%) and the balsamic vinegar was an inexpensive type. The Granny Smith is a tart green-peel apple.

• 1 hothouse cucumbers
• 1 Granny Smith Apple
• 225 grams of smoked salmon
• 1 bunch watercress
• Half a lime
• salt

and for the dressing

• 2 large strawberries
• 12g of chocolate
• 1 tablespoons of balsamic vinegar
• 2 tablespoons of walnut oil

1. Wash the cucumber well. Place it on a cutting board and run a peeler once over the top of the cucumber removing one strip of the peel. Discard it. After that use the peeler to cut the cucumber into thin slices. Go down about a third, and turn the cucumber upside down and repeat with the other side. After that rotate and slice the sides. Discard the core (or feed the chef). If the slices are wet, dry them with a paper towel.

2. Peel, core, and thinly slice the apple. Squeeze half a lime into a bowl, add about a teaspoon of water and 1/4 teaspoon of salt. Mix well and place the apple slices in the bowl. Using your finger tips coat the slices with the mixture.

3. Thinly slice the salmon (the brand I buy comes sliced) and cut the slices into strips about the size of the apple slices.

4. Remove stems from watercress. Wash and dry leaves.

5. Distribute the cucumber slices and watercress to four quarter plates. Shake off excess liquid from the apple slices and mix with cucumber and watercress. Place the salmon over the vegetable bed.

6. In an oven proof measuring cup place the chocolate and a teaspoon of water. Melt the chocolate by microwaving the chocolate and water for 15 seconds or less. Remove from microwave oven and mix in the walnut oil with a small whisk.

7. In the small bowl of a food processor place the two strawberries, the oil and chocolate mixture, and the vinegar. Process until smooth. Serve the dressing in small cups with the salad.

I have to double the recipe for the dressing when serving individual portions or it looks too little in the cups. If you are mixing the salad ingredients and the salad dressing before serving, use a bit less than the full amount given in the recipe.

QED in the kitchen

My cookies are burning, so now I’m baking rocks. I have been baking different recipes for biscotti (that is what cantuccini di Prato are called in the US) hoping to write a post on the hows and whys of biscotti, but my biscotto bottoms kept burning. My oven seems to heat up fine despite its 22 years, so I attributed the burning to my inexperience. Things had to improve.

To tame the glowing coils in my oven, I placed four rocks inside to act as temperature trackers. Combining the stone baking experiment with some reading on the science of cookie baking I got my biscotti to stop burning.

Bakers needs to be aware of many oven details to avoid those burnt cookie bottoms. As ovens are different, what may work for one oven may ruin a recipe in another. So I will break this post into two parts: first will be a modern explanation of how an oven heats up. This story is at the heart of modern physics. Next week’s part will include a few practical things to avoid those burnt bottoms.

Just atoms and photons

To bake the dough one needs to raise its temperature. The oven does that by transferring heat to the dough. Heat and temperature are both properties of collections of things — such as atoms, electrons, or photons. The flame in a gas oven or the coil in an electric oven provide the heat needed for baking, but at a temperature much higher than the what any recipe calls for.

Everything you see around you is made of atoms that are in constant motion. These atoms interact with each other and with the environment by throwing and catching particles of light called photons. To understand heat and how it differs from temperature start out by thinking of atoms and photons as small billiard balls. The atoms that make up your computer may appear to be still, but they are moving, just like the atoms in the air you are breathing. The difference is that atoms that make up the computer dance around one spot, whereas the atoms in air fly away once exhaled. Every atom is moving with a different speed and their average speed (in some weird units) is their temperature. If you were very small, say the size of a grain of dust, air atoms would jostle you. Even if you started out still, the energy from the collisions would set you in motion. A bit like bumping into someone standing still on ice. That energy in the motion of atoms is what is called heat.

Atoms cannot really collide with each other. Instead, once near, they throw photons at each other (an atomic snowball fight), and it is the photons that collide with the atoms. Once in a while, if atoms are jiggling from some previous atomic snowball fight, they will throw a photon that could go on forever. These are the photons we call radiation or electromagnetic waves. The more an atom is jiggling, the bigger the punch it can pack into those radiation photons. We see as blue a photon with a lot of energy and as red those that have a bit less punch. An infrared heating lamp will give out lots and lots of red photons. A laser pointer much less. Both are more or less the same color, but the lamp will warm you up and the laser won’t. Similar temperatures, different amounts of heat.

The flame or coil heats up everything in direct sight by radiation and heats the surrounding air that collides with it. That hot air then rises as a whole and circulates in the oven, a process called convection. That motion is on top of the natural random motion of the air. If the warm air happens to be near what you are baking it will transfer some of its heat to the food, cool down, and drop to the bottom, where it will once again warm up by collision with the heat source. The walls of the oven also heat up and radiate their own photons, some of which will get absorbed by the food.

Watch on Vimeo

The slow warmth of rocks

I brought the four rocks in from the cold of winter and placed them in a pre-heated oven. The oven had been set to 175ºC and after ten minutes my oven thermometer reported 170ºC as the inside temperature. The rocks slowly warmed up.

As the oven warms up the air inside expands as each molecule of air moves around a bit more. At room temperature (25ºC) there are about 90 grams of air in the oven, but as it heats up to its baking temperature (170ºC) a third of the air leaves the oven through the inside vents and the door seal. If the oven had food in it and not rocks, the food would give out steam that competes with the air for space, and some of that moisture would also leave the oven.

After 70 minutes the rocks had yet to reach a stable temperature. How long food take to reach a final temperature depends on:

• How heavy it is. The bigger the mass, the longer it will take.
• How fast it can absorb the heat. The thermal conductivity of a material measures how easily atoms moving in one end of the material affect the motion of atoms at another end. In non-scientist units, where water has conductivity one, air will have have a conductivity of 0.04 (so it’s a bad heat conductor, or an insulator), stone about 4.5 (so it conducts heat better than water), stainless steel 28, and aluminum 430.
• How easily it can be heated up. If the same amount of energy goes into different materials, their temperatures will change by different amounts. The higher the material’s heat capacity the harder it is to raise its temperature.

All these variables make it hard to guess how long something will take to heat up. And to complicate things, the shape of the food and what happens to its moisture matter a lot.

In the oven, the temperatures of rocks A and C are higher than those of rocks B and D. Rocks A and C are in the back part of the oven where there is no glass window for the radiant heat to escape. There is also a difference between the bottom of the rock and its upper part.

The part of the rock towards the heat source can be 15ºC hotter than the parts away from the heat source. That is 27ºF more: enough to mess up baking times. The table shows the average of a few measurements I made. The On column averages measurements taken right after the coil of the oven went off; the Off column, averages of measurements taken after the coil had been off for 3 minutes. Notice that Rock D on the lower rack has a lower temperature on its upper surface than the rock on upper rack (and the data did not get swapped). I would put the measurement error at 5ºC or less.

		Off	On
Rock B	top	172	173
	bottom	180	182
Rock D	top	165	164
	bottom	172	181

The lower parts of the rocks are exposed to the very hot photons that come from the coils when they turn on. A glowing orange coil has a temperature between 500ºC and 1000ºC, much hotter than the temperature we would like to keep the oven. These hot photons are responsible for my burnt cookie bottoms.

Next post I will outline what I did to get my oven to bake better.