The Fermometer


We’ve changed the Fermomter.  It has a higher range and suggested fermentation temperature range bars for red and white wines and Belgian ales have been added.

We changed the range to accommodate zymologists of all kinds.  We dropped lager conditioning temperatures because after fermentation, the wort temperature is close to ambient temperature.  In raising the range, we also get the added advantage of observing temperatures as they drop towards pitching temperatures if not sufficiently cooled.

Remember, these are broad suggested temperatures.  Each yeast has it’s own sweet spot and every brewer or winemaker seeks a temperature that suits their particular style or taste.  Just about every yeast producer list fermentation temperatures on their packages.  Links to various fermentation temperature suggestions and yeast producers websites are listed here.

We didn’t set out to make the least expensive one, we set out to make the best one!

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 44 to 86 degrees Fahrenheit with temperature indicators every 2 degrees.  Interpolation allows for one degree temperature determination.  It sports suggested ranges for the fermentation of both ales, lagers, Belgian Ales, as well as red and white wines  These are broad guidelines only and it is suggested that you follow the yeast manufactures recommendations for the correct fermentation temperature.


The Fermometer is easy to use. Simply peel off the paper on the back and attach it 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.

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.  Wet t-shirt evaporative cooling counts as continual exposure and is not recommended.   Like beer, liquid crystals to not like ultraviolet light.  Do not expose your 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.  The simple answer is that it is very close to the temperature of the fluid in the fermenter.

To answer the question in more detail, 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 water temperatures measured by an immersion thermometer as the water came into equilibrium temperature with the outside temperature.

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 follows:

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

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

20-30 degrees difference between ambient and internal temperature  ~ maximum 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.

Do not judge the accuracy by waving it around in the air and seeing multiple crystals in different locations “lit”.  It is sensitive enough that it is affected by variation in air current temperatures.  It must be attached to the fermenter for accurate and stable readings.