Since we launched MyBrewbot I've been asked by a number of people, how accurately does the device track fermentation?
Well, from the evidence of around 50 brews we'd have to say pretty accurately.
Firstly, a caveat. There is no substitution for taking a hydrometer reading at the end of the process to confirm that you've reached your target specific gravity. What MyBrewbot helps you with is to know when to do it.
Secondly, we all know that pensive feeling we get having spent 6 hours slaving in the brewery. Getting our efficiency right, sanitising everything, oxygenating the wort, pitching the yeast and setting the temperature in the fermentation fridge.
Then the wait........
Has fermentation started? Do I need to do something? Where are those first bubbles?
Well, do not despair. The very first thing MyBrewbot tells you is whether fermentation has kicked in. How do we know? We'll see the ambient temperature begin to drop as the yeast start to ferment and produce heat. The temperature controller kicks in and starts to demand cooling. The ambient temperature starts to drop. All things being equal, there is no reason for the ambient temperature to drop other than the yeast's exothermic activity as it starts to ferment your wort.
Here's the moment when a Weiss beer I had on last week started it's fermentation.
The yeast had been pitched at around 13.00 hrs on the same day. There were no bubbles as yet - but the drop in ambient temperature (blue line) was a sure fire indication of fermentation activity. Point to note, the led in the top right is showing blue - meaning cooling is being demanded.
Here's the same beer 5 hours later. I've switched to the 1 day view now to show entire progress.
Now we are seeing some cycling of the ambient temperature. We're not quite sure what causes this - but clearly the yeast are working hard, then slowing. Maybe it's cell reproduction. No doubt some clever biologist will be able to give us some insight.
Nonetheless, what is clear is that as fermentation gets more vigorous so the yeast produce more heat, the fridge cooling system works harder and the ambient temperature drops. At this point (8am in the morning) occasional bubbles are seen emerging from the blow off tube. Point to note - the led is now showing white - telling us that neither heat nor cool is being demanded. Both are switched off.
Here is the same beer 30 hours after pitching.
There is vigorous bubbling now. The fermentation is going full steam. The ambient temperature is just under 11 degrees - that's half of the target temperature! At this point we took a sample for the hydrometer and the SG was logged at 1047. a .004 variance. Pretty close.
Now we'll switch to the week view at 07.42 - 48 hours after pitching.
The Weiss is still bubbling vigorously but the ambient temperature is on the rise. Peak fermentation has finished. Another sample was taken for the hydrometer and read 1038. A .005 variance.
Here the beer is done. It's been in the fermenter for 6 days. The ambient temperature is now just 3.5 degrees below the beer. A final sample was taken which read 1008. Bang on for the yeast we were using. Also notice that since Saturday the amplitude of the ambient temperature has increased and it's frequency has decreased - presumably as the yeast cells have less and less sugar to eat.
Points to note - the led has changed to red - indicating that heating is being demanded. Also, temperature control is (ever so slightly) less accurate. You can see more of the green (beer) line peeking out of the red (target). We believe this happens because of the decrease in frequency of the yeasts heat generation.
So whats the conclusion?
I think it's fair to say that MyBrewbot charting gives a pretty accurate picture of the yeast's fermentaion progress and that the algorithm for estimating specific gravity throughout the process is good enough to ensure that you only sample your beer once at the end of fermentation.