/ thermometer

Temperature Calibration

As a result of last week’s issues relating to making syrup and temperature control, I thought it would be a good time to address calibration of your thermometer at home or how to get by without one!

Lab Calibration

This might sound obvious, but contact your manufacturer. If you happen to have the widely popular Thermapen or any other Thermoworks product and you suspect you’re out of calibration, you can send it back and they’ll take care of it for you. If it’s found to be because it’s defective, they’ll replace it for you. If not, you can have their calibration lab recertify your product (although this is not a free service). CDN, which makes another thermometer popular with homebrewers also indicated they’d take care of a defective product free of charge.

Home Calibration

So let’s say you didn’t buy a fancy thermometer from a company that offers calibration and you’re not really interesting in sending it off to a NIST lab for certification. What can you do to calibrate your thermometer at home? Fortunately, it’s easy. I like a two point calibration method, although a single point can be used if you’re pressed for time or just aren’t looking to be that precise. The first data point you’ll need is what the thermometer reads at freezing (32F or 0C). This is also the data point you’d use if you’re only going to use a single data point. To properly measure freezing, you need to make an ice bath. Fill a glass full of ice. Crushed ice is better than ice cubes. You want to now fill the cup with water, leaving approximately ½” (~1.25cm) of ice sticking out of the top of the water line. Stir gently and the leave the cup alone for approximately 2 minutes. Now submerge the thermometer 2” (~5cm) below the waterline and stir slowly. Some thermometers might take up to 10-15 seconds to settle on an accurate reading.

Make note of the temperature. If you can manually adjust the calibration on your thermometer, do so while stirring until your thermometer reads freezing properly. If you’re doing the one point calibration and your thermometer has no calibration adjustment, you’re done. The correction factor of your thermometer is the difference between freezing and the measurement you made. Be sure to add this correction factor to every measurement you take.

If you want a little more accuracy in your correction factor, you need a second data point. Now you’ll need to measure boiling water. Don’t forget when calculating what boiling should be at your location, you take your elevation or barometric pressure into account. Fortunately, there’s a website to help you do just that. At the time of my measure, my barometric pressure was exactly 30.00“Hg, so my boiling point should read as 212.1° F. Once we have this measurement, we can make a chart to tell us what the correction factor will be at any given reading.


What can we tell from this experiment? My thermapen and cheaper thermoworks thermometer are right on the money, no correction necessary. As you can see, their correction plots sit right on top of the ideal temperature line. This remote control temperature probe needs to go in the trash. If I were going to use it, I would have to refer to the chart shown here to interpret what the thermometer read verses what the actual temperature would be.

The Decoction Method

Since we love to do things the hard way at Immaculate Brewery, who says you need a thermometer at all? They didn’t use them for hundreds of years, so how did our brewing forefathers do it? They knew of two ways to measure things; body temperature and boiling. If you heat water to body temperature and then add grain, that coincidentally makes a great acid rest. Now you have a mash that’s slightly below body temperature … now what? You pull a measure of the mash, bring it up to a boil, then add the boiling mash back to the original container to bring the remainder of your mash up to the next rest temperature. How much mash should you pull? Use the following formula:

*Vdecoction = Vtotal mash * [(Trest - T0)/(Tboil - T0)]*

I would add at least an extra 10% overhead on top of that to account for the heat absorption of the mash tun and the fact the decoction will cool down a bit from boiling before you get to fully stir it all back into the mash. Some things to note about decoction is you want the grain to steep in the water for 15-20 minutes before pulling your first volume for boiling. This allows the enzymes on the grain to go into solution. Then when pulling your decoction volume, make sure it’s thick, like oatmeal. The reason is twofold; one, you want to leave as much enzymatic power in the mash tun as possible. Two, you want as much starch in the decoction because the act of boiling it bursts the starch molecules open and makes them more readily available for the enzymes to work on. If you’re not being too strict on following traditional methods, it is a good idea to hold your decoction in the mid 150’s °F (~68 °C) for 15-20 minutes to allow any enzymes in the decoction to work on conversion. This will give you a slightly better overall conversion efficiency. If math is not your thing, it works out to a little over ⅓ the volume for the first pull to get you up to a reasonable saccharification rest and a little under ⅓ to get from saccharification to mash out. If you are interested in a little more detailed information on decoction, head over to Braukaiser's webpage.

Mrs. Carys Method

Quite possibly of the most interesting methods of the bunch doesn’t require anything more then some boiling water and your senses. In a handwritten beer recipe discovered in a colonial Virginia plantation, the mash in procedure is described as

… let your water boil then & put into your Mashing tubb, When the Steem is gone off, so as you may see your face; then put your malt ...

So to be clear, boil the water, cut off the heat, wait until no steam is coming off it, then add the grain. Could mashing really be that simple? I suppose it must be seeing as people were making beer for hundreds of years before thermometers, but this still seems almost too easy. To test the efficacy of this method, I heated 1 gallon of water until it hit a rolling boil, cut off the heat, then waited to see what happened when “the steem had gone off”. The temperature was then recorded. This procedure was followed 3 times. Remarkably, my results reflected that of the BYO author as you can see.

The second trial I believe I was a little slow to measure the temperature which would explain why the reading a tad lower, but this would still result in a reasonable mash temperature. Perhaps a bit dry by modern standards, but yeast wasn’t as attenuative back in the day, so I could see how this would make a very reasonable beer.

There you have it. Plenty of ways to figure out the actual temperature for your mash. Give one a try and let me know how it worked out for you!