In brewing, many different measurement devices can be used.† The majority of the measurements I make revolve around temperature, and specific gravity. The reason for this page is so someone else might learn from my trial and error.† No measurement device is a true mistake, it is just that some are much better than others.† No measurement device should be used unless it is calibrated, checked for calibration, or corrected for temperature if needed.
There are many, many types of thermometers brewers can use.† Most of them are either bi-metal, or glass.† Here is a picture of a few of the types I have at home, and have tried in brewing.
The three glass thermometers one the left are floating thermometers.† I have found floating thermometers to be fine in a mash so long as then are not hit and broken, but the glass topped one can get really hot, and the rubber topped one next to it can lose itís rubber top.† None are acceptable in hot water.† The center one is an absolutely wonderful device.† It was given to me, but I have seen them for sale at Williams Brewing. It is extremely accurate, and works well in a mash.† All of the glass thermometers are slow to respond to temperature changes.
The other three types are bi-metal.† The dial thermometer in the center is fine if calibrated, but slow to respond to temperature changes.† The digital thermometer/timer on the bottom is also slow to respond to changes, and not a great choice for brewing.† The digital display thermometer at the top right is wonderful.† I got it for about $12 at a local WalMart.† It has performed flawlessly, and even came with an extra battery.† It also responds very rapidly to temperature changes.† I use it everywhere in the brewing process that a temperature measurement is desired.
Specific Gravity Measurement
There are basically two different ways to measure Specific Gravity as a homebrewer.† One you simply cannot do without, well, sort of.† They are a hydrometer and a refractometer.† A hydrometer is a wonderful device, but liquids at temperatures higher or lower must have their readings corrected.† A refractometer uses light and a prism to measure the Brix of the liquid.† ATC models will automatically correct the reading for the temperature.† This makes a refractometer ideal for hot wort like runoff.† A reading of beer after fermentation with a refractometer will be incorrect, and there is a correction factor, but it is not a simple equation.
Here are some of the hydrometers I own, and my refractometer I recently purchased.
The hydrometers I have are dramatically different.† On the left is the basic triple scale hydrometer.† It is a piece of crap IMHO. In the past I used it when I thought I might break a hydrometer due to warm liquids. On the right of the triple scale is the hydrometer I prefer to use.† I got it at Williams Brewing for the same price as a triple scale.† This hydrometer has markings for every reading of the hydrometer.† Hydrometers are fragile instruments. I keep no less than 3 on hand at any given time.† I tend to break them and other glassware
On the right is my ATC refractometer.† A true work of art.† I calibrated it and use it to measure the Brix of hot wort.† I purchased it from Northern Brewer for the unheard of low price of $60.† It is great for OG of beer as well.† For SG, I still use a hydrometer, but Domenick Venezia has a great page entitled Refractometers that explains how they work, and a Formula Page that has formulas for refractometers near the bottom.