Hi all
Just monitoring my first fermentation using the BrewPi. Everything is going great, but I was wondering one thing:
Is there any way you can tell the approximate activity level of the fermentation using the temperature graph? Perhaps the difference between fridge temp and beer temp?
Cheers!
I think the closest would be to make a bubble counter, you can roughly determine the amount of co2 being let out that way wich translate into yeast activity.
But, the beer should be warmer when it is actively fermenting due to the exothermic reaction that is occurring. As such, should the fridge not need to work harder (i.e. go to a lower temp) to counteract this heat being generated? If this is the case, could you not tell at least something from the beer temp reading and the fridge temp reading?
Personally, I do believe you can. Just like you mentioned, during more vigorous fermentation, the exothermic nature causes the freezer to work harder. Below is a screen shot of the first few days of my recent brew. The set temp was 60.5 and you can tell when the freezer is working harder and then when it lightens up do to less frictional/exothermic activity. I use stainless conical fermenters so there is no visual feedback outside of airlock activity. I used this as an indication that it was time to raise temp a small bit.
But, I am working on my bubble logger too 
if you wanna calculate yeast activity by comparing the wattage used, then the surounding area need to be a constant temperature, so the thermal loss is identically all the time. if you can do that, then its only a matter of making a few tests with a fermenter filled with water, and compare the differences between water and beer over the same period.
You totally can use the total control “volume” to see if your fermentation is active. Unfortunately, but the brewpi software is missing one thing, which is the control system’s integrated on-time (more on that later).
According to Watlow,
W = (Liters * temp rise in C) / (0.790 * heat up time)
Using this equation and watching an uncontrolled fermentation batch, I figured that a 19L (5 gallon) batch undergoing a vigorous fermentation was making about 8 watts of constant heat. With convective losses and a large delta above ambient, this number can be significantly higher higher (but since I have a plastic fermentor, not as high as for a conductive metal).
On the flip side, I now have a double TEC controlled setup using a high power motor controller (from Pololu). I am able to monitor the current output to the TECs and can estimate total current consumption. Full bore, I’m can put 90W to the TECs, effectively pumping < 50W of heat (TECs are terribly inefficient). With PWM control, I cut that down to about 75W and < 35W pumped and am holding steady. The extra overhead is due to the plastic fermentor wall being a terrible conductor – I lose a lot to ambient.
Since I know the power draw of my system and resulting TEC pumped, if I took the raw data from the brewpi, I could determine total power input (or heat extracted) from my tank.
While fun – I just look at the level of fridge activity at the end (like bryancm1)
Happy brewing!
