Need help monitoring specific gravity or alcohol content

[Malkavian]

So in addition to being a newbie electronics hobbyist, I'm also a pretty accomplished homebrewer. For a while now I've had in my head an idea for monitoring fermentation progress via a PIC and an RS232 or USB link to a PC.

My problem however lies in the proper way to monitor fermentation. The way I see it, it could be done several ways, either via specific gravity of the solution, or alcohol content, or sugar content. I don't really even need to know absolute numbers, just the rate of change as fermentation proceeds. All the ethanol sensors I've found so far only function in a vapor environment (i.e., for breathalyzer type applications) and a refractometer type device typically requires a small sample of a known size.

I feel sure there's something I could be overlooking here but at this point I have no idea what it is, and can't really move on with the project until I figure it out. Any suggestions to that end would be extremely appreciated


Cheers
-Evan

[EEPROM777I]

~Deleted~

[Externet]

Hi.
If a refractometer works for your application, the task is to find one for continuous monitoring via USB or RS232, not a typical batch one that needs periodical manual sampling.
Would you say a stirrer or circulator (to constantly refresh the sampling) and a plain (serial output) batch-type submerged refractometer could provide readings versus real time?
Would a serial pH probe tell you anything in the ethanol process? Sorry, am not an expert in the field, but find your task interesting.

If not much success here, try : http://www.scienceforums.net/forumdisplay.php?f=11
It is not exactly for professionals, but there is some quite resourceful geniuses (to my opinion) there.
Miguel

[Malkavian]

The submerged refractometer idea seems interesting; can you point me in the right direction to explore those further? I did some basic googling for different kinds of refractometers but my search terms must have been such that i didn't see that particular type of device.

Given the batch size that I work with (23L range) a recirculator might not even be necessary, just some basic filtering to keep solids from corrupting the refractometer's readings.

[Externet]

Hi. Sorry I edited my message above after your quick response.

By stirrer or circulator I mean some method of renewing the sampled fluid in the plain refractometer to provide real time measurement, as am also not aware of a non-batchy device for this.

More geniuses (some harsh) also here:
http://groups-beta.google.com/group/sci ... cal/topics

Miguel

[jwax]

How about monitoring the carbon dioxide output of the batch? Are you using an air trap? Perhaps you could count bubbles optically.
signed,
Another brewer.

[Bob Scott]

What's wrong with the usual recommended method of monitoring the specific gravity of the batch (wort or mash etc) with a floating hydrometer?

Any refraction method will be hard to do, since all that yeast floating around will scatter the light unless you filter every sample.

Hey! Maybe if you get a refractometer with the right density, you could float it on top of the batch. When it sinks, the batch is done! hehe

Bob
Yet another amateur brewer.

[philba]

I agree, there is a lot of gunk in the wort and I think it will clog up many things. I would look into using capacitance. I'm thinking of a pair of plates that have a dielectric float in between them. As the specific gravity decreases the float will sink lower, thus decreasing the capacitance. Since the plates would be above the wort, they wouldn't get gunked up. Calibration could be done against the manual unit. The capacitance can be measured pretty easily in a number of ways, especially with a micro.

You might also be able use a submersed capacitance probe but I don't know how much of the dielectric effect is due to sugar.

[bodgy]

If you pop over to the competitor (Circuit Cellar) last year or earlier this year there was a brewers comtrollerPID heater controller as a project.


Colin

[Engineer1138]

I've never brewed beer, but I have given quite a bit of thought on monitoring the progress of fermentation when I make wine.
Idea #1 is a modified floating hydrometer whose position can be measured. Drawback is that bits of the must can affect how it floats, so the normal thing is to spin the hydrometer to clear an area first. Hard to do automatically.

Idea #2 is a refractometer that uses a sampling pump to draw in a fixed and filtered amount before measuring. Drawback is that I would also have to automate cleaning the reservoir and all tubing after each use.

Idea #3 (most promising) is a bubble counter that records the frequency of CO2 bubbles past a sensor. The frequency will increase as fermentation peaks and diminish as the wine is ready to be racked. Perhaps also measure average bubble size as it may correlate to vigor of fermentation.

But in the end I decided that I liked the winemaking process enough to stay "old school" with everything

ps,
thanks for reminding me that I have to get some yeast to make my first batch of mead!

[Malkavian]

What's wrong with the usual recommended method of monitoring the specific gravity of the batch (wort or mash etc) with a floating hydrometer?

Nothing's wrong with it per se, I'm just interested in being able to monitor yeast performance without having to open the bucket/carboy; mostly to see how yeast responds to different temp ranges, high starting gravities and the like.


I like the sound of the capacitance idea, just need to do some work to see what other elements of the wort (hop alpha acids, etc) do to modify it. Perhaps a floating dielectric would be the best way to get clear of that obstacle.

Thanks for all the suggestions guys, I'm finally getting somewhere

[jwax]

Engineer- The bubble counter makes the most sense to me. Hell, you could put a microphone next to it and count the clicks, plot vs. time.
Mead? OMG! My batch of that prehistoric vile fluid was horrid! Maybe the honey was foul.

[Malkavian]

Engineer- The bubble counter makes the most sense to me. Hell, you could put a microphone next to it and count the clicks, plot vs. time.
Mead? OMG! My batch of that prehistoric vile fluid was horrid! Maybe the honey was foul.

THREADJACK! How long did you age it? PM me if you like with the specifics, maybe I could diagnose it

[philba]

I'm not sure you can actually threadjack your own thread!

anyway, another thought - I assume that you are trying to determine when fermentation is complete. Specific grav is certainly one way. when it stops decreasing, you are done. I'm a big fan of capacitance (as noted above) but am not sure you could build a probe that wouldn't get effected by the byproducts of fermentation. Anything that comes in contact with the wort will get all sorts of gunk on it so the bubble counting approach has some potential.

I'd try something along these lines: use a dark colored/IR-opaque liquid in the fermentation lock and arrange for the bubbles to go through a tube that runs between an LED and phototransistor. You should be able to adjust it so that when the bubble goes through the dark liquid, the PT pulls it's collector low and thus get a pulse. It would need good light shielding but should be workable. I'd also use a Schmitt trigger so you don't see multiple transitions per bubble. You can track rate of fermentation via the bubble period.

If you could determine bubble size, you could even calculate volume of CO2 production. My zymurgy is pretty hazy but I think there is a way to equate CO2 production to sugar conversion and thus you could determine alcohol content. I think it is 1 Mole of sugar produces 2 Moles of alcohol and 2 Moles of CO2. You'd have to factor in pressure and temperature to convert volume to mass but I bet it could be pretty dependable.

[Malkavian]

Well, I'm looking for being able to find when fermentation is complete of course, but I envision being able to plot rate of change of the SG, which would give me a clear idea of how the yeast activity ramps up, and then tapers off.


That would be achievable by monitoring CO2 I'm sure, but I think it may be a little less direct, and I'd have to design an airlock that would continue to 'bubble' distinctly in even a vigorous fermentation, instead of just becoming a continuous stream of bubbles that a photodiode might not be able to distinguish.

Equation of CO2 production to sugar conversion is the key, I'll have to ask a bio chem professor at my alma mater and see if I can shed some light on the subject.