The Fermometer

The Fermometer is a liquid crystal display thermometer designed to monitor the temperature of the fermentation process with convenience and precision and without the sanitation concerns of immersion thermometers.  It has a temperature range of 36 to 78 degrees Fahrenheit with temperature indicators every 2 degrees. Interpolation allows for one degree temperature determinations.  It sports suggested ranges for the fermentation of both ales and lagers.  These are broad guidelines only, and it is suggested that the brewer follow the yeast manufactures recommendations.

The Fermometer is made of mylar to be water resistant. Easy to read two color graphics are printed on the back side of the top layer. This keeps the graphics from scratching and keeps the Fermometer looking brand new.


The Fermometer is easy to use. Simply peel off the paper on the back and attach to the outside of your fermenter with the self-adhesive backing.  Be careful.  Once you stick it on, it won't come off without damaging the unit.  It is best to stick it at mid-height on your fermenter to average out any stratifications in temperature that may occur once the fermentation calms down.

Reading the temperature is straight forward.  If one crystal is highlighted in green, it is that temperature.  If two adjoining crystals are highlighted in blue and tan, it is the temperature in between.

Advice on yeast pitching temperatures vary.  Some say you can pitch at the top of the recommended range and let your wort continue to cool to the targeted temperatures. This has the benefit of letting the yeast reproduce earlier and reduce the lag time. Others say let the wort cool until it reaches the targeted temperature.  In either case, minimize temperature fluctuations as much as possible.

The Fermometer was designed to provide years of trouble free service.  There are only two don'ts.  The Fermometer™, like all LCD thermometers, is water resistant, not water proof.  While it can easily be rinsed or washed with traditional cleaning and sanitizing solutions, it should not to be continuously exposed to these or other solutions for extended time periods.  Such exposure will result in water seeping between the laminate layers and discoloring the crystals. Like beer, liquid crystals to not like ultraviolet light.  Do not expose your beer or the Fermometer to sunlight for extended periods of time.


People have often inquired about the accuracy of the fermometer and what it is measuring when placed on the outside of the fermenter in contact with ambient air.  To answer those questions, I conducted an experiment where I put warm water in a glass carboy and placed the entire setup outside in thirty degree weather and compared the fermometer to internal temperatures measured by an immersion fermometer as they came into equilibrium.

What I learned is that for every ten degree difference in temperature between the atmosphere and the fluid in the fermenter, the temperature was off by approximately one degree as follow.

0-10 degrees difference between ambient and internal temperature  ~ 1 degree difference between fermometer and immersion thermometer

10-20 degrees difference between ambient and internal temperature  ~ 2 degree difference between fermometer and immersion thermometer

20-30 degrees difference between ambient and internal temperature  ~ 3 degree difference between fermometer and immersion thermometer

So in most normal fermentation situations, the fermometer is only off by about 0.0 - 0.5 degrees from the internal fermenting temperature.