We’ve heard of chefs who claim that they can tell temperature by pressing a thermometer to their lips. Setting aside the problem that this technique could lead to a trip to the emergency room, the approach seems highly vulnerable to human error. Leaving temperature control to intuition is a recipe for disaster: dry and rubbery chicken, under-cooked fish, and scalded milk. What’s more, when cooking at low temperatures, being off just a degree or two can make your food not just unpalatable but downright dangerous to eat.
That’s why the most important tool in your kitchen is a quality thermometer, followed closely by a setup that allows you to set the temperature of the cooking environment with precision. With temperature under close control, chefs can relax and devote more of their creative brain power to flavor combinations and new textures.
Cooking food sous vide (sealed, in a low-temperature water bath) is one of the easiest and most affordable ways to achieve such control. Modernist Cuisine and Modernist Cuisine at Home include hundreds of our favorite recipes for sous vide dishes. We exploit this technique, for example, to slow-cook chicken to juicy perfection while also pasteurizing it, which requires a minimum holding time at the final temperature to knock any germs down to a safe level. It’s crucial to be able to trust your thermometer, because if it reads 60° C / 140 °F when the temperature is actually several degrees cooler than that, the chicken may not be fully pasteurized when you serve it.
Fortunately, high-quality thermometers are widely available and relatively inexpensive. We prefer digital thermometers because they are easy to read and switch instantly between Celsius and Fahrenheit. Moreover, better models, such as Thermocouple’s Platinum RTD probes, are accurate to about half a degree Celsius (a bit less than one degree Fahrenheit). Even inexpensive digital oven probes are accurate to within 1.5 °C / 2.7 °F, even at low temperature. Analog thermometers, in contrast, are all but useless at low temperatures, and spike-and-dial varieties typically vary up to 2.5 °C / 4.5 °F from the true temperature.
These accuracy numbers all presuppose that your thermometer is properly calibrated, not a safe assumption for many off-the-shelf products. So whenever you buy a new thermometer, calibrate it right away by using the simple, tried-and-true method of verifying that it reads 0 °C / 32 °F in water stirred with crushed ice and 100 °C / 212 °F in water at a full boil (but note that water boils at lower temperatures at elevations above sea level, so you may need to look up the normal boiling temperature at your location). Be sure the thermometer probe doesn’t touch the sides of the container, and give it a few minutes to settle on a final reading. If your thermometer hits these targets on the nose, it is suitable for sous vide and other low-temperature cooking methods. But if your thermometer is off by 2 °C / 4 °F or more, return it for a new one or take it to a professional to adjust it.
Once your thermometer is dialed in, you can move on calibrating other parts of your kitchen. You probably won’t notice a difference in your cooking if your oven is off by a degree or two, but if you can’t set an oven temperature below 200 °F / 95 °C, it isn’t suitable for dehydrating food or slow-cooking a frozen steak to medium rare. Because ovens are notoriously inaccurate at their lower ends, be sure to calibrate your oven at several lower temperatures before relying on it for slow baking or braising.
To calibrate your oven, you need a thermometer with a probe and digital display, tethered together by an oven-safe wire. Preheat your oven fully to its lowest available setting (give it a little extra time to settle), and then clip your probe to the oven rack so that the tip of the probe is near the center of the cavity and points upward and inward. Close the oven door, wait a few minutes for the oven to recover its temperature, and then note the temperature you set as well as the reading on the thermometer. Repeat with the probe placed near a back corner and then near the door. Next, increase the temperature by 30 °C / 50 °F, and repeat. It takes some time to record these measurements for the entire range of your oven, but you only need to do it once, and the resulting picture of your oven’s performance is invaluable. You may learn, for example, why your quirky oven burns cookies on the right side of the sheet even while cookies in the back left corner stay stubbornly raw. Oven walls radiate heat unevenly, so you should expect to see some temperature variations within the cavity. Once you know their magnitude and location, you can compensate for them.
As in an oven, the temperature inside your refrigerator is warmer on some shelves than others; the door compartments are often the warmest. This can pose a safety risk if the temperature in any part of the refrigerator exceeds 5 °C / 40 °F. It is wise to set your refrigerator to a temperature that causes lower shelves to drop below freezing if that is what must be done to keep the top shelves in the door within a safe range.
To test the temperature of your refrigerator, place glasses of water in it at various locations, including the door and the top and bottom shelves. Wait several hours and then measure the temperature of the water (take care not to let the probe touch the sides of the glass). Adjust the refrigerator setting if needed, and then repeat to confirm that all parts are at or below 5 °C / 40 °F.
When cooking or cleaning up after a meal, never put food in the refrigerator or freezer while it’s still hot. We used an infrared camera to visualize how much a bowl of hot leftovers warms the surrounding food in the refrigerator, and the results were shocking. The temperature can rise dramatically and stay above the safety zone for hours, long enough for food to spoil.
Finally, use a thermometer rated for subzero temperatures (many digital ones aren’t) to check the temperature inside your freezer. Generally speaking, the lower the better, because fast freezing produces the smallest ice crystals and the least damage to foods as they solidify. But as long as the temperature is -15 °C / 5 °F or lower, you needn’t worry about microbes multiplying in the frozen food.
No one claims that calibrating your kitchen is fun. But it is important, and once you’ve done it, all your cooking will go more smoothly. You can then focus more of your attention on the creative aspects of cooking without worrying so much about being thwarted (or even made ill) by the vagaries of temperature.
Click here to put your newly calibrated oven to use, cooking steak straight from the freezer!