Thermometers What's best for Brewing and How to Calibrate!

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One of the important items often overlooked in brewing is the simple thermometer. Most dial indicator and electronic thermometers have a means to adjust them if they are calibrated incorrectly at the factory or are knocked out of alignment, but many times people leave it to chance that the manufacturer did this for them already.

A bottom mounted thermometer. Image courtesy of fdog.
When I purchased a smoker grill, a friend advised me to calibrate the dial indicator thermometer on the grill before I used it, using an ice 'slurry'. My findings were that the thermometer was 10 degrees too hot, and needed adjustment. For this particular thermometer, the adjustment is a nut on the backside that had to be turned with a small wrench.
With water and mash temps being critical for making good homebrew, spend some time testing your thermometer before using it, and calibrate it if it is off. Even if a thermometer is new, don't automatically assume the factory set the temps correctly. Even if they have great quality control, something could have happened in shipment to affect that. Same goes for existing thermometers, test them periodically to see if they are still accurate.
There are many different types of thermometers, and most all of them can be used for brewing, but there are strengths and weaknesses to each, which I will outline below

Types of Thermometers:

Dial-type thermometers are mechanical in nature, and this type of thermometer has a needle that swings across the face of the instrument to show the temperature, connected to a bimetallic coil strip/spring inside the housing. The adjustment for these is typically a small screw or nut on the back side of the thermometer that allows you to adjust the needle. By adjusting it you are winding the coil more loosely or tightly when you turn the adjustment.
The benefits of this thermometer type are that they are simple to adjust, they are cheap, and widely available. The simple design does not require batteries or much concern in keeping it dry. The negatives of this type are that like anything mechanical it needs more care to keep it in calibration, and the 'read' on the thermometer is not as quick as today's digital thermos.
'Mercury' thermometers use a liquid inside a glass tube which rises as heat is applied to the 'bulb' end. I use the term mercury thermometer loosely, since I haven't seen a true mercury thermometer since my childhood. Mercury is toxic, and most, if not all liquid thermos today are fluid filled (not mercury). Again, these thermometers are cheap and readily available.
For years I used a 'candy thermometer' from a discount store for keeping my temps in check. These generally float, which is a positive. They aren't the easiest to read at some angles, are relatively slow to read, and there is no ability to adjust them. If they are off, your only choice is to be aware of the 'offset' between the actual and the measured value, and compensate for that. An example would be if you tested alongside another calibrated thermometer and the value was high by 10 degrees, you would have to subtract that from each of your readings. These work by the expansion of the liquid as it is heated, which forces the liquid upward in the thermometer housing.
Some fluid-filled thermometers are acrylic encased, and others are glass. This to me is a huge negative when working around food or drink. Broken glass is not an adjunct any of us care for in our beer, and aside from that if we bump this type of thermometer off a table it is going to shatter and make a mess that can injure someone.
Digital thermometers come in all shapes and sizes. They use thermocouples to read temperatures with relative speed. A thermocouple is generally two dissimilar conductors that form one or more junctions, and it is at the junctions where the temperatures are read. For most digital temp probes, this is at the very tip. The difference in electrical current is used to calculate the temp. Since everything is digital, most have a circuit that will allow you to calibrate the thermometer by manipulating a button, switch or screw. Some digital thermometers are water proof, some are water resistant, and some are not designed to be used around liquids. Do your homework to understand the differences, and look for one with an IPX4 rating for splash-proofness.
You need at least a splash-proof one, since you may accidentally dunk it, or handle it with wet hands. Some more expensive models are sealed and allow immersion, but I see no need for this unless you want extra dunking insurance, since you only need to immerse the tip to get a reading.
Some digital thermometers have replaceable probes, and others are built-in and are not. You also can get probes that can stay in constant immersion if you like, and you can get various lengths of probes for many models.
The benefits of digital thermometers are a quick read with a nice digital display (some are even backlit) and almost all of them have a function to switch between F and C. The replaceable probe feature is nice, since the brains of the thermometer are in the base, and a faulty/damaged probe can be detached and replaced.
The downside of digital is that they can be expensive if you want one with an extremely quick read. Additionally, they take batteries that have to be replaced. They are more prone to water damage than a dial or fluid-filled thermometer, since there are electronic components that make up the system. However, a good quality digital with splash-proof features is reliable and not terribly susceptible to water intrusion, but you could permanently damage one if you dropped it into near-boiling wort for a long period of time.
Strip thermometers are useful for applying to fermenters, and use liquid crystals to produce a color change at a particular temp. These are sometimes used for forehead thermometers, and aquariums/herpetariums. At least one company makes a 'thrumometer' that uses the same technology to measure temps flowing through an aluminum tube, so output of a liquid can be measured. These would not be useful for measuring mash or strike water temps, since they cannot take the heat. Additionally, if you do use them on fermenters be aware they are not very accurate and they do not hold up well to water. The good news is they are cheap, and cannot be broken (although water immersion will damage them to the point they stop working).
Infrared thermometers are handheld and are the only 'non-contact' thermometer in the list. I find tons of uses for them elsewhere, but not in my brewing. This type takes its measurement by the amount of infrared radiation emitted by the object it is pointed at. I find most bargain IR thermometers to be highly inaccurate. If you run across one, point it at your hand or arm, and note the temp variance. My IR thermometer typically reads 85F on human skin, when that should be closer to 98.5F. That is quite a bit of variance. Additionally, with the steam involved in brewing, I am not sure how an IR thermometer would work. If anyone is using one for brewing with success, please post that in the comments.
So which is best? Based on the pros and cons of each, I'd say for measuring water and mash temps your best bet is a good digital thermometer (something like a Thermopen or Thermopop), or if that is not in your budget find a good dial thermometer that can be calibrated and is easy to read. If you go digital, find one that is rated IPX4 or IPX7 for water resistance. Also consider the battery type and how readily you can get those batteries at your local store. An auto-off feature can help prolong the battery life.
Regardless of which type you get, ensure that it covers the temperature range for brewing.

Left to Right: Candy Thermometer, Frying thermometer, Brewing thermometer, Dial Thermometer (shown for example only, I don't see anyone needing 700 degree wort! This was from the dome of my smoker),Thermapen insta-read digital.
Maverick smoking thermometer (note the high reading. The probe is not designed to read below 100 degrees). I included this to show an example with a detachable probe.
So I have my thermometer now, how do I calibrate it?
  1. Take crushed ice (cube ice works too, but I'd suggest crush in a blender) and add it to a glass. Fill the majority of the glass with crushed ice. Add a small amount of tap water. You want the crushed ice consuming volume from the bottom of the vessel to the top. If the ice floats off the bottom, pour off some water or add more crushed ice.
  2. Let the temp stabilize for 2-3 minutes.
  3. Before taking the reading, ensure the ice is not floating. Again, pour off any water to get the ice to sit once more on the bottom.
  4. Insert the thermometer and gently stir the ice 'slurry'. Try not to touch the walls of the container. The goal here is to gently mix the solution so there aren't pockets of heat.
  5. Check the temp on the thermometer. After stirring for a few seconds the temp should read 0C or 32F. If it does not, refer to the manufacturers guidelines on how to adjust your thermometer. If you don't have a manual, the web is a terrific place to find one.

Note in the pic the thermapen is right on the money...
Once you have your thermometer dialed in, happy mashing!
Nice write up on different types of thermometers.
Maybe it depends on which bargain IR thermometer you have, but the one I got from Harbor Freight has a 0.5F resolution and the accuracy is about 1F when measuring boiling water.
There is both an offset and gain error associated with any measurement equipment. Checking at just one temperature will only account for offset. To compensate for both you need two measurements. More details on my blog here:
When checking your thermometers accuracy using body temperature keep in mind that your skin is colder than the inside of your body.
Please read up on IR thermometers before you criticize them. Stating that they are inaccurate because you pointed one at your skin is not valid. Skin temperature varies widely and is almost always less than 98.6F
The real reason IR thermometers are not suitable for home brewing is they read differently based on a material's emissivity. Aluminum has an emissivity coefficient of something like 0.09, so pointing an IR thermometer at your aluminum brewpot will be meaningless.
I happened to be brewing a batch yesterday and my digital probe thermometer was acting up. I grabbed an IR thermometer and it was reading about 5-10F low @ 165F when pointed at the steeping water. This makes sense because water's emissivity coefficient is 0.95.
In a pinch you could use IR, but you need to know how the device interacts with the target.
I agree, Nice write-up on the different styles. As for calibration, 32F is good but 2-point calibration is better. Thermoworks, the makers of the thermapen, have a good video/tutorial on calibration.
Ideally, since we as brewers care about temperatures within a couple degrees of 152F, that is the best point to calibrate. But there-in lies the problem, how do we know we have 152F? Boiling and freezing are the two easiest points.
Agree about infrared thermometers. Your skin is NOT 98.6 degrees. Open your mouth and hit the infrared there - you'll be a lot closer.
I actually use mine a lot for brewing. It tells me when I'm in the neighborhood of a boil, the rough temp (good enough) for dry yeast rehydration, etc. I use a digital immersion for the mash but don't discount infrared. Its actually one of my most-used kitchen tools.
You can get a digital thermometer for $10-20. May not be "instant read", but besides the "Therma-pen", Thermoworks makes a model RT100C, which is nice for about $20.
Not as much a criticism as an observation. I agree the example I used the prove the point is not the best example, but for the cheaper ones they aren't very accurate and I have proven that through testing of my own.
Anything that isn't in contact with the fluid is going to be less accurate by design because it is not in contact with the fluid you are measuring.
IR thermos also average the temp for an area, so the farther you are away the more of an average reading you get. At 23cm, my gun shows it is measuring a 2cm spot. At 96cm, that spot is 8cm.
IR thermos are a surface measurement tool, and different substances have different emissivity, which also poses an issue for using them for brewing.
That, plus the steam generated in the brewing process to me make IR thermos less useful. I do own one, and it has its place, but not in my brew equipment. They are great for non-contact where you aren't concerned about a high degree of accuracy. For strike water, mash temps, and fermentation temps where degrees matter I'd opt for a large dial, or accurate digital (and as was pointed out, no need really for a high-dollar fast read one)
I tried the IR (it is calibrated) as a goof and because it looked like my digital thermo was dying. I was surprised when it read the water temperature consistently.
I will be buying a dial thermometer before my next batch. The experience taught me that a spare would be cheap insurance.
With the exception of the frying thermometer, from the picture it looks like you broke into my house and stole all of my thermometers!! Spot on including colors and models.
Nice write up!
I think George is talking about the Thermopop which is also manufactured by Thermoworks. Model# TX-3100. It comes in 9 different colors, superfast read, backlit, and splashproof.
Weber makes a decent digital read thermometer for around twelve dollars.I checked mine in boiling water and it was within 2 degrees.Weber is a good brand and twelve bucks is about 85 dollars less than a thermopen.Just sayin.
Originally I got the Thermapen on an open box sale.
If you sign up for their email list, they draw for a Thermopen give-a-way each month. Of course you get spam from them from that point on...The benefit is they will notify you on open box sales.
I paid about 60% of retail for mine, and it came with a warranty. I got it for smoking meat, where opening the grill and waiting for a temp reading means you are losing moisture and heat. I use it for brewing and smoking.
The thermopop is much cheaper, same manufacturer, and is a quick read - although not quite as fast as the pen.
The RT600C from same company looks promising, and is dishwasher safe to 190F! It too is a fast read. I may get one of these for a backup.
i check mine by boiling water,unless you live in high altitude water boils at a set temp...
This is a great article. I recently asked some questions in the Equipment and Sanitation Forum. Something I seldom see discussed is equipment accuracy. I recently purchased some cheap temp displays from Amazon to tape to my carboys so I can see the temperature without removing the towel. I also plan to use them for monitoring bottle temp during carbonation. What I found is they are not too accurate.
Highlighting my issue, I have found that some thermometers are able to be calibrated. Digital scales are also usually able to be calibrated. I have remarked most of my plastic buckets as I found they are off as well.
As for thermometers, the best one I have found for the money is the EXTECH TM25. accurate, simple and I now have two of them that replaced my Taylors.
I now calibrate all my thermometers with both ice and boiling water.
I totally agree. You should also take it one step further and correct of elevation and atmospheric pressure. Luckily the Internet can be a beautiful place. Here is a handy calculator:
@mrstevenund A two-Point calibration will only work if you live at sea level. If you adjust your thermometer to read boiling at 212 and you live above sea level, you will end up mashing several degrees (depending on the altitude) below your target temperature. Or find the theoretical boiling point for your given altitude, and calibrate accordingly.
I am going to throw my hat in the ring in favor of glass thermometers.
I have a mercury glass thermometer with a nickle-cadmium armor cover.
The Thermometer comes with a certificate of accuracy, traceable to the National Institute of Standards and Technology (NIST). NIST Certification is the the gold standard in precision.
The armor cover allows me to use the 12" long thermometer to stir the mash, thereby making sure I am getting the most accurate and consistent temperature reading.
As for broken glass... I treat them like my glass measuring cup, I don't knock them off tables.
Go old school my friends: use glass thermometers and glass hydrometers for accurate readings.
I am going to throw my hat in the ring in favor of glass thermometers.
I have a mercury glass thermometer with a nickle-cadmium armor cover.
The Thermometer comes with a certificate of accuracy, traceable to the National Institute of Standards and Technology (NIST). NIST Certification is the the gold standard in precision.
The armor cover allows me to use the 12" long thermometer to stir the mash, thereby making sure I am getting the most accurate and consistent temperature reading.
Go old school my friends: use glass thermometers and glass hydrometers for accurate readings.