49 replies to this topic

[davelew]

Still what I don't understand is why someone hasn't developed some sort of hydrometer that is integrated into these fancy conical fermenters.

To get an accurate hydro reading, you're supposed to degas the sample. A few CO2 bubbles on the hydro can change the bouyancy and throw off your reading. Kind of hard to do that in a sight glass.

[3rd party JKor]

Anyone have an idea of what the max CO2 evolution rate would be for a 10 gallon batch?For a 6.5% ABV batch you should evolve about 1000L CO2 (as associated with EtOH production). If you stretch that over a week you get an average of 94 mL/min, but obviously the majority is on the front end so the average doesn't tell you much. I need to know the evolution rate in the initial stages of fermentation to size the flow meter.Anyone have a plot of gravity versus time for a typical batch? I may be able to extract from that if the data collection rate is high enough.

Edited by JKoravos, 31 May 2009 - 09:10 AM.

[3rd party JKor]

Just as a point of contrast, I don't take any gravity readings whatsoever after I test for O.G. Somehow my beers still turn out great.

Believe me, I've subscribed to that method as well. But I'm a process control guy by nature, I can't escape it. I'm always thinking of ways I can improve control on my process. Generally, I don't have the time, money or inclination to implement my ideas, but I'm ramping up to do a major brewery overhaul, so these things are on my mind.

[chuck_d]

Anyone have an idea of what the max CO2 evolution rate would be for a 10 gallon batch?For a 6.5% ABV batch you should evolve about 1000L CO2 (as associated with EtOH production). If you stretch that over a week you get an average of 94 mL/min, but obviously the majority is on the front end so the average doesn't tell you much. I need to know the evolution rate in the initial stages of fermentation to size the flow meter.Anyone have a plot of gravity versus time for a typical batch? I may be able to extract from that if the data collection rate is high enough.

It would be very difficult I think to mathematically determine the rate of CO2 evolution. It depends on many factors, like temperature, pressure and interfacial area between the gas & liquid. Even in the brewing literature I have that discusses ways in which to increase gas the gas exchange rate, they don't discuss how to calculate the amount of time it takes to do it (typically the reverse process but the concepts are mostly the same). As for a graph, there a was a thread on here I think recently where someone posted their gravity vs days graphs.

[3rd party JKor]

It would be very difficult I think to mathematically determine the rate of CO2 evolution. It depends on many factors, like temperature, pressure and interfacial area between the gas & liquid. Even in the brewing literature I have that discusses ways in which to increase gas the gas exchange rate, they don't discuss how to calculate the amount of time it takes to do it (typically the reverse process but the concepts are mostly the same).

Well, I just need a really rough estimate for meter sizing. There are many things affecting how much CO2 is exiting the fermenter, but the main driver is fermentation rate (at least, I'm assuming it is). If I can get a good bead on that I can size the meter.

As for a graph, there a was a thread on here I think recently where someone posted their gravity vs days graphs.

I saw that. I'll have to look around, I can't remember which thread it was in.

[chuck_d]

Well, I just need a really rough estimate for meter sizing. There are many things affecting how much CO2 is exiting the fermenter, but the main driver is fermentation rate (at least, I'm assuming it is). If I can get a good bead on that I can size the meter.

Word, yeah, what I'm saying is that in all my reading, a lot of which has been calculuations involved in the various parts of brewing, nobody has touched that subject except to say that it's extremely variable, but there are things you can do to make it faster. I wouldn't think it' solely dependent upon the rate of fermentation, I would think that the rate of fermentation drives how much CO2 is in solution, but then you end up with unknown pressure differentials between the beer & what's in the headspace & what's outside the fermenter. I think that the best approach might be to just calculate the total CO2 that is going to come out and then figure like 90-95% of it will come out in the first 4 days, that'll give you the average rate and then maybe double that for max rate. I was going to say +85% of the rate to get the max but really I'm just making these numbers up.

I saw that. I'll have to look around, I can't remember which thread it was in.

Yeah, me neither. I looked here and the other place by for some reason it didn't jump out at me.

[davelew]

There are some graphs of extract concentration vs. time in this paper:https://www.homebrew...rmenting_LagersYou might be able to back-calculate the CO2 evolution from the slope of the dashed line for the 12P beers

[chuck_d]

You might be able to back-calculate the CO2 evolution from the slope of the dashed line for the 12P beers

The dashed line is diacetyl, I think you mean the dash-dot-dash lines which represent extract. Yeah, you might be able to back-calculate CO2 production, but not evolution from these.

[3rd party JKor]

Thanks Dave. I should be able to get something out of those plots.

[davelew]

Chuck: Yeah, you're right, it's the dash-dot-dash line, I should have read the legend more carefully. As for CO2 production and evolution, I was thinking of assuming that the beer was saturated with CO2 before the line starts to level off, so the high point of evolution would also be the high point of production (although the peak wouldn't last as long).JKoravos: Keep in mind, that paper is about lagers instead of ales, and is about commercial processes instead of homebrew scale, but it should at least get you an idea of the range you'll need to measure.

The dashed line is diacetyl, I think you mean the dash-dot-dash lines which represent extract. Yeah, you might be able to back-calculate CO2 production, but not evolution from these.

[3rd party JKor]

Using the slope of plot B, I get 151 cm3/min.Dave, I noticed they were lagers. That initially concerned me, because we as homebrewers generally consider lager fermentations slower, but looking at the plots (specifically the fermentation only lasts 4 days. In any case, the gravity drop is pretty linear, which makes sense if you look at the yeast life cycle, but I hadn't really thought of it that way. I was assuming the gravity drop was more like an exponential decay.If you assume the gravity drop is linear, you can imagine a "worst case scenario" where you're brewing a high gravity beer that drops 90 gravity points in 4 days. That would give a CO2 production rate, related to alcohol production, of 300 cm3/min. I think that's probably a good jumping off point.

[MolBasser]

I would think it's consistent because the there is a precise amount of carbon dioxide produced for each unit mass of sugar that is converted to alcohol. The ratio of monosaccharides to disaccharides may effect the number, I'm not sure though. I still need to do some more research. I bet Basser could shed some light on the subject.

The amount of gas produced is precisely known. For every glucose that enters the EMP pathway you get 2 CO2 molecules.If you know your starting gravity, you know you sugar amounts and by measuring the amount of CO2 that is evolved you can precisely calculate the current gravity of your beer.It should be very straightforward if you can accurately measure the gas.BrewBasser

[3rd party JKor]

The amount of gas produced is precisely known. For every glucose that enters the EMP pathway you get 2 CO2 molecules.If you know your starting gravity, you know you sugar amounts and by measuring the amount of CO2 that is evolved you can precisely calculate the current gravity of your beer.It should be very straightforward if you can accurately measure the gas.BrewBasser

Thanks, BB.AFAYK, are there any side reactions going on that would generate enough gas to throw off the reading?

[MolBasser]

Thanks, BB.AFAYK, are there any side reactions going on that would generate enough gas to throw off the reading?

Not unless you have a serious bacteria infection.....BrewBasser

[stellarbrew]

JK, I'm curious about the type of flow meter you were looking at, and what kind of precision you would expect. Have you made any preliminary selections?

[chuck_d]

The amount of gas produced is precisely known. For every glucose that enters the EMP pathway you get 2 CO2 molecules.If you know your starting gravity, you know you sugar amounts and by measuring the amount of CO2 that is evolved you can precisely calculate the current gravity of your beer.It should be very straightforward if you can accurately measure the gas.BrewBasser

BrewBasser, isn't CO2 also released in sterol synthesis? And also in the metabolism of amino acids? People can use CO2 as a guide to how much the gravity has dropped, but I'm not certain that it is entirely from the EMP pathway. When looking at Fix's Principles in Brewing Science p. 96 I see a CO2 coming out of the transformation of mevalonic acid to squalene. Admittedly I don't know much about that reaction other than it takes energy from the yeast cells to do it, but it does look like 1 CO2 molecule is a by product. In Brewing they mention something on p. 332 about an aldehyde and a CO2 being the by-product of amino acid metabolism. Just curious what that's all about.

[MolBasser]

i agree with what was said above. there are a lot of variables to think about like the amount of c02 that gets dissolved in to the beer even during fermentation, and also if the temp of the head space in the fermenter has any influence on the expansion of the carbon dioxide molecules too,possible false reading. I would be more concerned with a false C02 reading from some of the dissolved C02 though. does that make any sense to anyone else?

The amount of gas dissolved in the beer is very straightforward to calculate given that it is at atmospheric pressure. There are tables in almost any hombrewbook that will tell you how much gas is in the beer at a given temperature and pressure. You can safely assume that it will be saturated during the fermentation.BrewBasser

[3rd party JKor]

JK, I'm curious about the type of flow meter you were looking at, and what kind of precision you would expect. Have you made any preliminary selections?

Omega FMA-1714. Purchased.

[stellarbrew]

Omega FMA-1714. Purchased.

Wow, expensive toy, but you'll have fun playing with it. It looks like it operates on the same principle as a hot wire anemometer. Are you having shop calibrated for CO2 at your expected temperature and pressure, or will you apply correction factors?I will look forward to hearing about your results.