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Is there any way, I can measure SG with a sensor of some kind? I guess I'm not REALLY after SG, but rather a way to determine that fermantation is done, without sampling.

I would very much like hook such a sensor up to a computer/microcontroller, and do constant (automatically) logging of the fermentation state, and post to a database.

I have tried to find any possible way to get this result, but I haven't really succeded, and I would to avoid, having to create some horrible device, that just reads from the hydrometer.

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If you ferment in a bucket, you can easily take a gravity reading without drawing a sample. – Tobias Patton Oct 18 '12 at 14:35
@TobiasPatton care to share how? – mac Oct 18 '12 at 15:36
Float a hydrometer in the bucket. – Tobias Patton Oct 18 '12 at 19:55
Why wouldn't you want to sample your beer? – baka Oct 19 '12 at 19:42
@baka, It's not that I don't want to sample it, I would just like to log everything, automatically, on the computer. – Nicolai Oct 22 '12 at 5:52
up vote 2 down vote accepted

The brewpi project is developing a SG sensor. Search for "digitial specific gravity sensor" on that page. Details are sketchy at present, but it's based on measuring boyancy force with a load cell. Elco, the project lead, says he's managed to compensate for drift which is one of the big problems with continual sampling against a load cell.

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Yea, I ended up on his site yesterday, and it sounds interesting. – Nicolai Oct 19 '12 at 5:28

The BrewBit, BeerBug, and brewpi are all setting out to do what you want on a homebrew scale - a sensor with realtime data. (The commercial market already has some, but they're beyond impractical outside a brewery setting.)

If I were you, I'd wait until the dust settles on this one, I'm thinking there will be lower prices, and better products in 12 to 18 months. Of course, if you think one looks REALLY promising, they all seem ready and willing to take your money via kickstarter!

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This thing has a hydrometer on a cable. I think it weighs the hydrometer continually, converts that to SG, and sends the output via wifi. The electronics sit on the top of your carboy, and the cable must go through some kind of seal.

This was probably a buzz marketing action, but I thought it was worthwhile to mention anyway.

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I'm guessing you will be logging the temperature as well? One method to tell that fermentation is done is that the temperature will start dropping.

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You could also look into trying to make a refractometer work. I actually sell SG/density and online refracs to the breweries. Nothing that you'd put in your home kit (unless you've got $10k laying around), but the refrac is actually a great way to measure actual concentration, where the SG/density can be effected by suspended solids and air. Not sure if one of the home/handheld refracs could be rigged up, but that might be worth a shot???

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