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Calculating Gravity Witout Removing Beer

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chrisedjohn

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I've been dreaming up a way to determine the gravity of my beer throughout fermentation witout sampling 8 oz at time and exposing it to oxygen and potentially infections. I'm thinking the ways I can do this would be to either accurately measure the weight of the carboy and beer and monitor it's change (i.e. the weight loss of carbon dioxide could tell me how much ethynol is present) or accurately monitor the volume if I could expect a reliable amount to be lost through fermentation.

Oh, and did I mention I'm cheap, so I'd rather make something than spend $100+ on an expensive scale? Between monitoring weight or volume, volume would be WAY easier for me to do cheaply and accurately, but I'm concerned about two things right now. First, after running some calculations of an average beer fermentation (i.e. 5 gal of OG = 1.040, FG = 1.005), I estimate a beer weight loss of about 1.44 lbs (of CO2). I can calulate the volume of the CO2 gas after it's left given the amount I expect to remain saturated in the liquid, but where I'm stumped is that after trying a few different approaches to calculating the expected volume left behind - I'm not seeing any measurable difference (actually even a slight increase).

So... I'm wondering if any of you, by practice or calculation, can attest to a measurable difference in volume during fermentation (given none was taken out and adjusting for volume changes due to temperature changes).

Thoughts?
 
though it may go against your desire for a DIY project, and make you spend a bit of money, i think i'd suggest you get a refractometer. Very easy to use and only requires a small sample. If you are worried about oxidation, maybe you could rig up a sample method that doesn't require you to open the lid. The meters can be had for cheap online and are very handy during the brew process, as well.
 
That or i have seen a few threads on brewballs... http://brewballstore.com
Little balls ya throw in carboy and all differnt colors....As they sink you know what your gravity is.

Maybe with a DIY project you could make something close to that...

Just an idea...........
 
Weight would be a very inaccurate method of determining anything, especially with the tools at the average home brew's disposal. You'd need to VERY accurately monitor CO2 production and temperature. If you fermentation reaches a temp of 70F internally at it's peak, but when you measure it's at 66F then you may have less CO2 than you expect to. A volume measurement would require you to know exactly how much yeast grew inside and how much is lost to trub/protein matter, which would also be very difficult to measure. Not that I want to discourage you, but I can't see being able to get a good reading out of all those variables.

My hydrometer tube only needs something like 4 oz, and I usually only check it a couple of time, so I don't feel I'm wasting very much. The others are right about the refractometer too, it's very handy and not super expensive.
 
Thanks for passing along that idea, winstonofbeer, that's exactly the type of approach I'm interested in. I'm sure a refractometer would be a great option, so thank you guys for vouching for that option, it's just not what I'm interested in exploring right now. I've got an itch to build or invent a clever solution - it's a puzzle I'm enjoying working on even though I know it's been solved by many before.
 
Build a sight glass off from the bottom of your fermentor vessel, only make it big enough to keep your hydrometer in. Not sure if you could read it/keep it from breaking during high krausen though!
 
One weight approach that would allow the use of a low-weight cheap scale: Make a balance beam and load one side with your fermenter and the other with an equal weight of water. If you attach the scale above the fermenter, it will register the loss of weight due to CO2 escaping.

I just set my original sample (minus a few QA sips) next to the fermenter and watch the hydrometer drop.
 
I can think of a way to reduce the contamination/oxidation potential; just take less gravity samples.:)

Almost all of the beer fermentations I've had went fine. Sure, I've taken gravity samples but 99% of the time I didn't need to, the beer was done and was ready to rack (this is assuming one has the patience to let the beer fully ferment without putzing around in it). If you make a good wort, pitch an appropriate amount of healthy yeast, and maintain decent temp control then almost every beer will ferment out fine (and many of the ones that don't won't benefit from any extra hydro readings anyway). If you're bottling and concerned with bottle bombs then it still should only take 1 'extra' hydro reading 99% of the time (because 99% of the time, if you were patient, it should be done).

Of those few brews that didn't ferment down as much as I wanted; all the hydro sample did was let me know a little earlier than I otherwise would have. Many times the next step is the same...rack it because it's done all it's gonna do.

Almost every batch I make has exactly 3 hydro readings total: preboil, OG, FG...that's it. None are taken out of the fermenter. Why are a bunch of extra readings needed?
 
Im with ya on that. . .I didnt even take gravity readings on my first two beers because I didnt have a turkey baster or graduated cylinder. Everyone here knows that fermentation looks like, and its pretty clear when its been done happening for over a week, OG and FG just tell me my %ABV.
 
You're spot on, SpanishCastleAle, I fully agree. My motivation here is admittedly for the pure pleasure I take in actively monitoring what's going on, as opposed to improving the beer. It's just really fun for me to watch the activity - I love the process.

Very interesting approach to ferment a seperate sample outside the fermenter, david_42. Do you think the difference in air exposure and/or mass (and therefore temperature rise and fluctuations) would significantly vary the progress of the "main" and "sample" fermentations? Ever measure a difference in SG between the sample and main at finish? Thanks for that idea.
 
You're talking about a glass carboy yes? Why not just drop a hydrometer in there and leave it. You can probably buy like 10 for the price of one refractometer.
 
Relating SG to a change in weight is a monstrously difficult proposition. You'd need to know the dissolved CO2 in your beer to have any reasonable estimate of the amount of sugars that have been fermented into alcohol.
To know this value for water, you'd need to know vapor pressure and temperature at the bare minimum (meaning you'd need to leave a thermocouple constantly in your beer). The additional dissolved solids in beer mean you'd need to know even more info.
This is a bad, terrible, bad, bad idea.
 
My experience is varied on the relative speeds. Once the sample stops changing, I draw a fresh one and it will either be the same or slightly higher. But the final gravity is always the same.

You have to pour the sample off to a glass and clean the tube & hydrometer occasionally. Towards the end, I put the precision hydrometer in.
 
I've been dreaming up a way to determine the gravity of my beer throughout fermentation witout sampling 8 oz at time and exposing it to oxygen and potentially infections. I'm thinking the ways I can do this would be to either accurately measure the weight of the carboy and beer and monitor it's change (i.e. the weight loss of carbon dioxide could tell me how much ethynol is present) or accurately monitor the volume if I could expect a reliable amount to be lost through fermentation.

Oh, and did I mention I'm cheap, so I'd rather make something than spend $100+ on an expensive scale? Between monitoring weight or volume, volume would be WAY easier for me to do cheaply and accurately, but I'm concerned about two things right now. First, after running some calculations of an average beer fermentation (i.e. 5 gal of OG = 1.040, FG = 1.005), I estimate a beer weight loss of about 1.44 lbs (of CO2). I can calulate the volume of the CO2 gas after it's left given the amount I expect to remain saturated in the liquid, but where I'm stumped is that after trying a few different approaches to calculating the expected volume left behind - I'm not seeing any measurable difference (actually even a slight increase).

So... I'm wondering if any of you, by practice or calculation, can attest to a measurable difference in volume during fermentation (given none was taken out and adjusting for volume changes due to temperature changes).

Thoughts?

Thought:

Or.... you could just not test your beer constantly and let it clear before even worrying about it.

I just finished telling another member in another post, but seriously this saves you so much stress and headache. And in reality, unless you are lagering, what is the point? Since I stopped doing this my brewing experience has gone from super involved every day or so if I have several batches on the go to:

- Brew day
- Bottling day after my beer has cleared if my SG is at the estimated FG point, usually after 3 weeks since I usually dry hop and do not use a secondary.

Thats 2 days. if you test all the time you are doing so much unnessecary work.

Edit: Now, if I am jumping the gun here and the purpose of your post was to explore an automatic gravity testing system, I digress... I think that would be kickass!
 
Relating SG to a change in weight is a monstrously difficult proposition. You'd need to know the dissolved CO2 in your beer to have any reasonable estimate of the amount of sugars that have been fermented into alcohol.
To know this value for water, you'd need to know vapor pressure and temperature at the bare minimum (meaning you'd need to leave a thermocouple constantly in your beer). The additional dissolved solids in beer mean you'd need to know even more info.
This is a bad, terrible, bad, bad idea.
NEGATORY

See this link, and download my spreadsheet.

I've been doing some experimenting with weight-based gravity readings lately. I'm getting extremely accurate results. Within 1 gravity point. I've started to take readings throughout the fermentation and I'm finding that the formula still works! As long as the fermentation has started, it appears that the wort quickly saturates with CO2 and the formula for calculating gravity based on weight loss holds true even during active fermentation.

I bought a 75lb. digital shipping scale off of ebay for about $35. It's accurate to 0.02 lbs. This is sufficient to get great results. For $35, you can have a real-time fermentation monitor. This is MUCH simpler, and I would think accurate and cheaper than trying to measure the actual volume of CO2 that is escaping through the airlock.

One caveat that I mentioned in the other thread is it may not work well if you use a blowoff tube.

You're welcome, good luck, and enjoy monitoring your beer's progress!:mug:
 
Thanks again everyone for your time and thoughful comments. Scone, thank you - that's the quick and cheap solution that'll scratch my itch to monitor fermentation w/o opening the airlock. I bought an extra hydrometer for $5, sanitized, and let it float in there. I just started my first lager and it's really fun for me to see that thing drop about 10 points in a day. It's impractical to get a precise reading with the krausen in the way, but I can still see it's "dropping" consistently. JJones17, you're right, this is unnessicary - my motivation is real-time monitoring for the pure pleasure of it. Earlytimes, rock on! It looks like you walked down the same bunny trail a year ago and actually caught the rabbit. Thanks - that'll save me some time (once I buy or rig up a way to accurately measure the weight).
 
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