Welcome back for part six of the fermentation instrumentation series. In part four, I placed a few different sensors in some actively fermenting beer to gather data. A week has now passed, and I've bottled the beer. Time to look at the data. Let's start with the device we know - the BeerBug.
We're lucky this time. New owners have just taken over BeerBug operations, and they're relaunching the product. Unfortunately, that means they're going through a bumpy transition period. While I was brewing, I could see the latest reading from my beer, but none of the history. But, after a lengthy email exchange, they have pulled through, and I have the data for this batch.
As before, I've uploaded the data to Helium's servers. This is mostly so I can use the same tools for processing the data for all three of the batches in this experiment. So, with out further ado, this is how the BeerBug thought the specific gravity of my English Mild changed over the week:
This is pretty typical. All the way at the left, we have the gravity that I specified as my starting point, what I read from my glass hydrometer: 1.039. The phenomenon that has been observed for every beer, but is as yet unexplained, comes next: the climb to a higher gravity. This probably has something to do with the initial yeast activity, as they rapidly reproduce throughout the beer, consuming the dissolved oxygen, and beginning to produce carbon dioxide. The gas exchange or cell proliferation may change the buoyancy observed by the BeerBug's float.
After the initial climb late Saturday, we dive right into the expected steady decline in gravity over the next few days. By night time on Tuesday, the gravity has nearly leveled off. A much slower decline continues as the few yeast cells that haven't starved continue to find some sugar to eat. By the time I bottled on Sunday, the BeerBug read 1.006. My regular glass hydrometer agreed ±0.001. That's pretty impressive.
The other thing that seems impressive is that there is far less noise in this data than there was in the BeerBug data from part three of this series. I think the explanation for this begins with the fact that there are fewer points in this dataset. In part three, there was a reading every minute. In this dataset, there is sometimes a reading every minute, but sometimes a reading only every 3, 5, or 10 minutes. This might represent a new strategy in the BeerBug firmware - if the measurement variation was white noise, averaging over longer periods should reduce it. Or, it could be just missing data, which would make the error band (the light blue) close in on the average (the dark blue), because the average *is* the data if you remove enough.
The BeerBug also has a temperature sensor in the housing that sits above (outside) of the carboy. Here is its data, in blue, with the temperature data we looked at from one of the Helium boards in part five of this series, in red:
The readings begin only a degree and a half or so off, but the drop into Sunday morning is deeper for the BeerBug. Its readings also stay consistently nearly 3ºC cooler. This was unexpected, given the placements of these sensors. The Helium sensor was closer to an external door, and the BeerBug was just a few inches above active yeast. I'll chalk it up to simple differences in the characteristics of the sensors, for now.
I've uploaded this data to a gist in CSV format, if you would like to examine it yourself. In the next post, we'll look at the data from the pressure sensor, and see if we can find a shape similar to the BeerBug's.
Update: part seven is live with pressure data.
Categories: Beer Development
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