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We fight to keep the fermentation temperature controlled, usually constant, but the fermentation is an exothermic activity, so in one side we try to remove energy, and in the other (inside, mainly in the middle), the energy is produced, and keep increasing along the fermentation.

So, if we measure the temperature in the fermenter walls we'll get one very near to the last one applied in the environment that is cooling the fermenter. But if we measure inside the fermenter (the wort), and keep going from edges to the center of the fermenter, the temperature grows progressively.

Considering the thermodynamics in fermentation when cooling is done from fermenter walls, if we measure the most hot point, we will have a lot of wort (in the fermenter edges) some degrees below the expected temperature. So if we measure it in the edges, we'll have a lot of wort (in the center) above the expected temperature. enter image description here

In the dynamics of fermentation temperature control, how/where is the best spot to measure the temperature ? Center, edges, 1/2 from the center ?

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The temperature will vary, but as fermentation proceeds we will be generating CO2 which aids convection within the fermenter. As such you should not see a large difference, but if you see any then measure 1/2 way.

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Depending on the type of temperature probe, you could use 2 of them in parallel, one in the middle of the wort and one taped to the side of the vessel to get a rough "average" of the reading of the two probes. Use the same probe type, wire, and wire length to help eliminate any difference in resistance that would affect the reading.

Mathematically it won't be a true average, but when we are talking a couple degrees of temperature difference, it would be close enough.

You can read more about it here, about 2/3 of the way down the page. (excerpt:)

Another application for thermocouples is in the measurement of average temperature between several locations. The easiest way to do this is to connect several thermocouples in parallel with each other. The millivolt signal produced by each thermocouple will average out at the parallel junction point. The voltage differences between the junctions drop along the resistances of the thermocouple wires. Unfortunately, though, the accurate averaging of these Seebeck voltage potentials relies on each thermocouple’s wire resistances being equal. If the thermocouples are located at different places and their wires join in parallel at a single location, equal wire length will be unlikely. The thermocouple having the greatest wire length from point of measurement to parallel connection point will tend to have the greatest resistance, and will therefore have the least effect on the average voltage produced.


That said, keep in mind that commercial fermentation tanks regulate temperature from the outside jacket, and rely on the convection current of rising CO2 bubbles to "mix" and make the temperature more consistent. Given all the variables, I doubt every square inch of fluid in a commercial tank is exactly the same temperature, and I also doubt that it matters all that much in the end.

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Measuring the wort temperature directly gives the most accurate information. To do this, you'll need to hook up a thermowell to your fermenter. There are a variety of styles for different types of fermenters.

The second best option is to tape the temperature probe to the side of your fermenter and cover with an insulator like styrofoam or bubble wrap. The reading won't be as accurate, but is good enough for most purposes.

EDIT: Temperature dynamics of the wort shall be the key to keep the wort homogeneous along the fermentation, and so, minimize/neutralize the effects of temperature elasticity. Take a look to the comments (where the issue and answer are discussed).

  • But, even in the wort (using thermowell), the temperature varies from the edges to the center, and varies a lot of degrees, so which is the best point to measure ? In the center ? At 1/2, 1/4, ... from the center ? – Luciano Jul 23 '15 at 12:21
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    "Varies a lot of degrees"? That certainly hasn't been my experience. When I ferment in my temp controlled chest freezer, the temp is amazingly homogenous throughout the wort – Denny Conn Jul 23 '15 at 15:19
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    The most important part to me would be to do a blind triangle tasting of a tightly controlled process vs. the normal process. If you can't taste a difference, the temps don't matter. – Denny Conn Jul 23 '15 at 19:49
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    The thermo-wells may have found themselves in natural convection currents, with higher-density, cooler liquids falling at the walls (closest to room temperature), and lower-density, warmer liquid rising in a central column (the center being the best-insulated area in the liquid). These are the same convection currents you would normally expect, along with the evolution of carbon dioxide, to drive strong currents that homogenize the liquid temperature of fermenting beer. The settings of your cooling controller may somehow respond differently to different control inputs, as well. – Franklin P Combs Jul 24 '15 at 0:25
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    I have to say I'd still be surprised if these currents weren't homogenizing the temperature nearly completely, but the very small differences could indeed be accentuated by the programming of your control setup and may help account for the wider fluctuation of observed temperatures. – Franklin P Combs Jul 24 '15 at 21:30

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