Common Sous Vide Problem

How do I know if the temperature reading on my sous vide immersion circulator or water oven is accurate?

Sous vide cooks (both commercial and home cooks) know that the stability of your water bath temperature is super important in sous vide cooking. All sous vide immersion circulators and water ovens come with an in-built temperature gauge. But how do you know if that temperature gauge is accurate?  Whilst most sous vide product brands work very hard to ensure consistency and accuracy of temperature readings, manufacturing errors can and sometimes do occur. So how do you overcome this problem? You measure the temperature of your water bath and the food in your food pouches with another thermometer.

Temperature matters in sous vide cooking

Food cooked sous vide retains important nutrients, is deliciously succulent and super flavorsome. This is because sous vide cooking is conducted at low temperatures. But cooking at low temperatures can also has less positive implications for the food you are cooking. eColi and other bacterial related concerns are very real. This is especially true in sous vide cooking where you are cooking meat over a long period of time.

According to the USDA, any food held in the so-called temperature “danger zone” (between 40°F and 140°F) for more than two hours presents a risk of food-borne illness from the growth of pathogenic bacteria — whether it’s cooked sous vide or by conventional means. Harmful bacteria can’t grow above that temperature, and at around 135ºF, most bacteria will actually be destroyed after a few hours, making pasteurization possible. The good news is that most home sous vide immersion circulators and water ovens will let you know when you’re cooking in the danger zone.

Checking the accuracy of your sous vide water oven or immersion circulator temperature gauge

So how do you make sure that the thermometer in your immersion circulator or water oven is accurate? You measure the temperature with another good quality thermometer. In sous vide cooking, there are two temperatures you will want to measure:

1. The water bath itself
2. The food inside the food pouches in your water bath

Photo credit: Amazon.com

Now let us be clear. You will not gain pinpoint accuracy when checking these temperatures. Don’t use this test to measure tenths of degrees difference for example. Your sous vide machine has a variance of 0.5 – 1 degree on average. This means you ARE likely to have some small differences in readings. But for example, if you noticed 2 degrees difference between your immersion circulator displayed temperature and the temperature on the second thermometer you are using in your last sous vide cook and say 5 degrees this sous vide cook, then something could be wrong.

Sous vide water bath and food pouch thermometer options

Jump on Amazon and you will find hundreds of thermometer options. You will see that there are thermometers at around the few hundred dollar mark right down to pocket change. It is most convenient to purchase a thermometer to measure both your sous vide water bath temperature (liquid) AND the temperature of the food in food pouches whilst in the water bath during your sous vide cook.

Quality is key here. You are literally making this purchase to ensure the food that you, your family and friends will be eating is safe and bacteria free. This purchase is to give you peace of mind. We are not saying you need to find the most expensive product on the market. But we are saying that you should look closely at the credentials of the company you are purchasing from along with reviewer feedback to make sure you are buying a reputable digital read thermometer.

Here’s what you should look for in a quality thermometer for your sous vide cooking:

• Is made with food grade stainless steel
• Has a degrees celcius and farenheit switch feature (this allows you to cook with recipes in each measurement system without having to convert all of the time)
• Operates with a wide temperature range
• Offers a warranty or satisfaction guarantee
• Is able to be calibrated
• If you are after versatility of use, is able to be used in an oven as well (many are not)

A very popular and reliable option to be used in your sous vide cooking is the Thermapen Mk4 by ThermoWorks. ThermoWorks hand assemble and hand test all of their products with a professional thermocouple circuit design. The Thermapen Mk4 is available in a variety of colors. ThermoWorks is a well respected and reputable brand in the sous vide cooking community.

It is important to note here that any thermometer you choose for measuring the temperature of the food inside your food bags will tell you the temperature of the meat, NOT whether it is done or not.

Sous vide food pouch temperature reading – you can’t just stick a needle in it!

Thermometers used to measure the internal temperature of food come with a probe. The probe is what you insert into your food to determine it’s temperature. In sous vide cooking you cannot just stick the probe or needle directly into your food pouch. If you do, the contents of your food bag will leak into your water bath. That spells the end of your sous vide cook and ruined food.

You need to use a sous vide foam tape such as the one offered by ThermoWorks. It seals your sous vide food pouch around the insertion point of the thermometer needle. (See picture left from sousvidecooking.org). This means you can measure the food temperature without leakage during insertion or after removal. Nifty right?

“Check your checker” regularly

OK. So you’ve used a thermometer to check your sous vide water bath temperature as well as the temperature of the food inside your food pouches. How do you know if the temperature on THAT thermometer is accurate? This sounds like consumerism gone mad doesn’t it. The good news is that you don’t need to get a third thermometer. You just need to calibrate your thermometer every twelve months or so. Calibrating involves checking, adjusting, or determining by comparison with a standard. This process ensures an accuracy of reading so that the thermometer can be used again and again with confidence.

Calibrating your thermometer is a quick and easy task.  Many analog and digital thermometers allow you to offset the temperature to adjust for the calibrated value. Here is how you can calibrate your thermometer at home:

Method 1: Ice Water

1. Fill a glass with ice cubes, then top off with cold water
2. Stir the water and let sit for 3 minutes
3. Stir again, then insert your thermometer into the glass, making sure not to touch the sides
4. The temperature should read 32°F (0°C).  Record the difference and offset your thermometer as appropriate

Method 2: Boiling Water

1. Boil a pot of distilled water
2. Once the water has reached a rolling boil, insert your thermometer, making sure not to touch the sides or bottom of the pot
3. The temperature should read 212°F (100°C).  Record the difference and offset your thermometer as appropriate

NOTE: The readings in iced water may vary slightly between -1 degree C and 1 degree C. The readings in boiling water may vary slightly between 99 degrees C and 101 degrees C using a pan of boiling water. Don’t use a kettle for this test.

Something to keep in mind

Sous vide cooking is designed to be enjoyable, fun and rewarding. By using a thermometer to measure your water bath temperature and the temperature of the food in your food pouches, you can be confident that each meal you prepare is totally safe to eat and enjoy. Whether you are cooking for one or a whole dinner party worth of guests, temperature gauge testing gives you peace of mind.

Photo credit: Kitchen Gizmo

Sous vide cooking is a great balance of science and creativity. But the science alone will not create the “perfect” meal every time. One person’s perfect “medium rare” might be another’s perfect “medium”. Even with the confidence that the temperature readings on your sous vide immersion circulator are accurate, there will be slight variations in “doneness” depending on your taste bud preferences.

Further resources and reading

What to look for in digital instant read thermometers

To learn more about sous vide cooking visit our FAQ and Resources pages.

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