[Big Monk]

I would just like to mention that the main benefit of my formulae is that it does work for fermenting wort. For the well-attenuated beer, Terrill's and my result aren't too different. I would say they're within an experimental error.

I find the opposite to be true. I brew only Trappist style ales and my attenuation is routinely > 85%. Your calculations seem to overshoot my actuals by a wide margin, in some cases as high as -0.006 S.G. Points from actual. I’m fairly confident I have entered the calculations faithfully in my spreadsheet, as they match the calculators that use your equations. 

For me, Terrill Cubic is king above 82% AA, and Terrill Linear for 78-82% AA.

I’ll also say that the above is true for values 4-6 points above final gravity as well, which is important for me as I use spunding.

[Robert]

But in the 50% range Petr has it nailed down.  Derek, I'm using your sheet  now and (provisionally)  cherry picking at each stage of attenuation guided by experience.  It's handy that you have all of the calculations laid out in one place.  Cheers.

[Big Monk]

But in the 50% range Petr has it nailed down.  Derek, I'm using your sheet  now and (provisionally)  cherry picking at each stage of attenuation guided by experience.  It's handy that you have all of the calculations laid out in one place.  Cheers.

Why are you raising the temperature again? Have you tried traditional cold fermentation and held at 45-48 °F the Whole time?

[Robert]

But in the 50% range Petr has it nailed down.  Derek, I'm using your sheet  now and (provisionally)  cherry picking at each stage of attenuation guided by experience.  It's handy that you have all of the calculations laid out in one place.  Cheers.

Why are you raising the temperature again? Have you tried traditional cold fermentation and held at 45-48 °F the Whole time?

Yes, I've done that.   I really don't want to derail this one a fermentation discussion, but :  each process in brewing has it's optimum conditions.  Think step mash.  Flavor maturation and attenuation are best achieved at 60°-64°F, and physical stabilization at 28°-30°F.  A compromise program of 48°-50°F and 37°-39°F misses the optima on both.  And it's not any more "traditional" if that matters.  It's based on the Summer or March beer process, rendered obsolete with refrigeration.  Traditional "Lager" or "Winter" beers were fermented more rapidly at warmer temps and held cold for as little as 7-10 days to clarify before serving.


BTW:  refractometer correction 0.97 OG 12.4°P FG: WRIf 6.0 saccharometer 3.1°P. 

[Big Monk]

But in the 50% range Petr has it nailed down.  Derek, I'm using your sheet  now and (provisionally)  cherry picking at each stage of attenuation guided by experience.  It's handy that you have all of the calculations laid out in one place.  Cheers.

Why are you raising the temperature again? Have you tried traditional cold fermentation and held at 45-48 °F the Whole time?

Yes, I've done that.   I really don't want to derail this one a fermentation discussion, but :  each process in brewing has it's optimum conditions.  Think step mash.  Flavor maturation and attenuation are best achieved at 60°-64°F, and physical stabilization at 28°-30°F.  A compromise program of 48°-50°F and 37°-39°F misses the optima on both. 

I was just assuming that you raise for a diacetyl rest, which typically is not required given cold temperatures, healthy pitches, step mashing/nutrient additions (wort production can affect nutrient levels in wort), etc. as the diacetyl precursor is less abundant.

Not knocking what you do, just bringing up another method that would save you having to raise the temperature, as well as eliminate the need for 50% AA checks. In the end you have a method that works in your brewery so I'm not trying to steer you either way, just curious was all.

[Petr]

I would just like to mention that the main benefit of my formulae is that it does work for fermenting wort. For the well-attenuated beer, Terrill's and my result aren't too different. I would say they're within an experimental error.

I find the opposite to be true. I brew only Trappist style ales and my attenuation is routinely > 85%. Your calculations seem to overshoot my actuals by a wide margin, in some cases as high as -0.006 S.G. Points from actual. I’m fairly confident I have entered the calculations faithfully in my spreadsheet, as they match the calculators that use your equations. 

For me, Terrill Cubic is king above 82% AA, and Terrill Linear for 78-82% AA.

I’ll also say that the above is true for values 4-6 points above final gravity as well, which is important for me as I use spunding.

Well, I have never seen so large difference between the two methods for fully-attenuated beers. Can you provide me with some of your data, I would like to check that out? The data that were used to get my formulae was from hundreds of samples, although the strongest was 18 P, therefore it is possible that for stronger beer it can be less accurate. Or it can be simply because of wort correction factor. What kind of value do you use?

In many cases, and I'm not saying it is your case, people misuse the refractometer and hydrometer. The wort correction factor is good example. I was quite lucky and my factor is 1.00, although it vary a lot, and I have friends that have 0.90 or even 1.1. If someone is using in good belief standard value of 1.04 it can be pretty far from the reality. A friend of mine has also a refractometer that he must calibrate on the water every single time before measurement. I just want to say that that cheap refractometers can be quite tricky to use accurately.

The accuracy itself is another issue. The hydrometer should be used with decarbonated wort only but not all of as do that. That can make difference order of 0.001 SG. Then there is a temperature, +-10F from calibration temperature can make +-0.001 SG. In case of the refractometer, they have usually accuracy around 0.2 Bx (0.001 SG) and into formulae you're feeding it twice. For beer before bottling it is often even worse, and the sample can be pretty fuzzy on refractometer's glass. So I would say, that you cannot expect the accuracy of FG from formulae to be better than 0.001-0.002 depending on particular circumstances, sometimes worse.

So, if all of these aspects are not ideal in some particular case, there is no point in chasing which formulae is better. In some cases, even worse formulae can give you better results if the input is not ideal it can cancel out some of that "non-ideality".

My formula is actually quite connected to Balling's formula that is widely used for its overall accuracy, although there could be cases when beer deviates from that formula, and there is no doubt about that even if it's less common than the other case.   

[Robert]

I've now measured 3 batches at FG since getting the professional brewery saccharometers,  and all 3 have shown Terrill new LINEAR to be dead on.  FWIW.  I'm convinced refractometers are good during mashing.  For chilled wort and fermentation, go with a floaty thing, not an optical delusion.

[Pricelessbrewing]

I haven't been following all 13 pages very closely, but I'm happy to see you on here now petr, and that there have been translations done.

Is the data you use publicly available anywhere?

Were different yeast types used and categorized? Specifically I'm interested in if the curve is different for diastaticus yeast vs brett vs more common ale or lager yeasts.

[Big Monk]

I would just like to mention that the main benefit of my formulae is that it does work for fermenting wort. For the well-attenuated beer, Terrill's and my result aren't too different. I would say they're within an experimental error.

I find the opposite to be true. I brew only Trappist style ales and my attenuation is routinely > 85%. Your calculations seem to overshoot my actuals by a wide margin, in some cases as high as -0.006 S.G. Points from actual. I’m fairly confident I have entered the calculations faithfully in my spreadsheet, as they match the calculators that use your equations. 

For me, Terrill Cubic is king above 82% AA, and Terrill Linear for 78-82% AA.

I’ll also say that the above is true for values 4-6 points above final gravity as well, which is important for me as I use spunding.

Well, I have never seen so large difference between the two methods for fully-attenuated beers. Can you provide me with some of your data, I would like to check that out? The data that were used to get my formulae was from hundreds of samples, although the strongest was 18 P, therefore it is possible that for stronger beer it can be less accurate. Or it can be simply because of wort correction factor. What kind of value do you use?

In many cases, and I'm not saying it is your case, people misuse the refractometer and hydrometer. The wort correction factor is good example. I was quite lucky and my factor is 1.00, although it vary a lot, and I have friends that have 0.90 or even 1.1. If someone is using in good belief standard value of 1.04 it can be pretty far from the reality. A friend of mine has also a refractometer that he must calibrate on the water every single time before measurement. I just want to say that that cheap refractometers can be quite tricky to use accurately.

The accuracy itself is another issue. The hydrometer should be used with decarbonated wort only but not all of as do that. That can make difference order of 0.001 SG. Then there is a temperature, +-10F from calibration temperature can make +-0.001 SG. In case of the refractometer, they have usually accuracy around 0.2 Bx (0.001 SG) and into formulae you're feeding it twice. For beer before bottling it is often even worse, and the sample can be pretty fuzzy on refractometer's glass. So I would say, that you cannot expect the accuracy of FG from formulae to be better than 0.001-0.002 depending on particular circumstances, sometimes worse.

So, if all of these aspects are not ideal in some particular case, there is no point in chasing which formulae is better. In some cases, even worse formulae can give you better results if the input is not ideal it can cancel out some of that "non-ideality".

My formula is actually quite connected to Balling's formula that is widely used for its overall accuracy, although there could be cases when beer deviates from that formula, and there is no doubt about that even if it's less common than the other case.

Thank you for this post Petr.

I want to be clear: I am backfitting old info. I have reasonable assurance that I was careful to calibrate and prepare samples but some of these batches are old.

I am going to be tracking your equations and Terrill’s in the foreseeable future to see if these new results square with the old stuff. The way my sheet is structured I can compare all 5 correlations simultaneously.

[Robert]

This is crazy.  We're all getting different answers.  Novotny and Old Cubic are most accurate for mine all the way across.

Been thinking about this whole thing.

I suspect a source of difficulty is the assumption being made that the only difference to account for between wort and beer is the presence of alcohol. In fact of course many other fermentation products are present (CO2 can be ignored as it is expressed from under the cover plate of the refractometer. )

The more I test, the more I find different formulae working at different times and in different batches.  The differences between the beers are seemingly minor and various:   slight variations in the blend of malts, amounts and varieties of hops used, attenuation limit, generation and pitch rate of the yeast, and so on.  (You know, always dialing in the recipe!)  But each of these factors could have a significant effect on the chemical composition of the fermenting/fermented beer, and I suspect in turn a significant effect on the refractivity index.   So every beer, or at least every set of samples produced identically, would really require its own correction formula.  And that formula could only be modeled retroactively once you already have a full analyses of the beer, and so would be superfluous.

  Refractivity and density just don't correlate except as determined for a specific substance.

[Big Monk]

This is crazy.  We're all getting different answers.  Novotny and Old Cubic are most accurate for mine all the way across.

Been thinking about this whole thing.

I suspect a source of difficulty is the assumption being made that the only difference to account for between wort and beer is the presence of alcohol. In fact of course many other fermentation products are present (CO2 can be ignored as it is expressed from under the cover plate of the refractometer. )

The more I test, the more I find different formulae working at different times and in different batches.  The differences between the beers are seemingly minor and various:   slight variations in the blend of malts, amounts and varieties of hops used, attenuation limit, generation and pitch rate of the yeast, and so on.  (You know, always dialing in the recipe!)  But each of these factors could have a significant effect on the chemical composition of the fermenting/fermented beer, and I suspect in turn a significant effect on the refractivity index.   So every beer, or at least every set of samples produced identically, would really require its own correction formula.  And that formula could only be modeled retroactively once you already have a full analyses of the beer, and so would be superfluous.

  Refractivity and density just don't correlate except as determined for a specific substance.

A good method would be to save wort from Losses and determine that batches correction after you put it into the fermenter. Essentially calibrate after racking over for every batch and log it into the spreadsheet. The. There is no guessing and the numbers for that batch are rock solid and stored for posterity.

[Robert]

Wort seems consistent with respect to my instrument's correction factor.  It's fermentation products other than alcohol, as I said, that I don't think are adequately accounted for.  (The only definitive test for alcohol content, after all, is to remove it and compare the weight or volume of the resulting sample.) The composition of the beer is complex and continually changing.  I have no doubt that some formula would work every time if all we did was progressively dilute the initial wort sample with pure alcohol!

[Big Monk]

Wort seems consistent with respect to my instrument's correction factor.  It's fermentation products other than alcohol, as I said, that I don't think are adequately accounted for.  (The only definitive test for alcohol content, after all, is to remove it and compare the weight or volume of the resulting sample.) The composition of the beer is complex and continually changing.  I have no doubt that some formula would work every time if all we did was progressively dilute the initial wort sample with pure alcohol!

I’m not big on variety so I think I’ll trust what I see after checking 5-6 batches with Hydrometer and Refrac. All my Trappist style beers have the same original gravity pre-sugar, so I’ll have one correction factor for all preboil wort, and then one separate fermentation correction factor for each beer.

[Petr]

I haven't been following all 13 pages very closely, but I'm happy to see you on here now petr, and that there have been translations done.

Is the data you use publicly available anywhere?

Were different yeast types used and categorized? Specifically I'm interested in if the curve is different for diastaticus yeast vs brett vs more common ale or lager yeasts.

Yes, they are. I used literature data (professionally obtained with way more accurate equipment that we usually have), the original article can be found here https://www.researchgate.net/publication/307794886_Convenient_Monitoring_Of_Brewery_Fermentation_Course_By_Refractometry.

It works for fermentation in general as long as yeast follow Balling's laws. I guess it should work for those that you mentioned but I tried that only on the bottom and top-fermenting yeasts of various strains. One small fermentation should be enough to validate it for you. Basically, you just need to confirm that the metabolism of those yeasts is or is not the same (for practical purposes) as for brewers yeast. I would say that chances are rather high that it is. 

[Petr]

This is crazy.  We're all getting different answers.  Novotny and Old Cubic are most accurate for mine all the way across.

Been thinking about this whole thing.

I suspect a source of difficulty is the assumption being made that the only difference to account for between wort and beer is the presence of alcohol. In fact of course many other fermentation products are present (CO2 can be ignored as it is expressed from under the cover plate of the refractometer. )

The more I test, the more I find different formulae working at different times and in different batches.  The differences between the beers are seemingly minor and various:   slight variations in the blend of malts, amounts and varieties of hops used, attenuation limit, generation and pitch rate of the yeast, and so on.  (You know, always dialing in the recipe!)  But each of these factors could have a significant effect on the chemical composition of the fermenting/fermented beer, and I suspect in turn a significant effect on the refractivity index.   So every beer, or at least every set of samples produced identically, would really require its own correction formula.  And that formula could only be modeled retroactively once you already have a full analyses of the beer, and so would be superfluous.

  Refractivity and density just don't correlate except as determined for a specific substance.

Yes, beer is a mixture of thousands of compounds but when compared to residual sugar, water and ethanol everything is negligible in terms of concentrations, their concentrations are a couple of order magnitudes lower than that "big three". Refractive index is concentration sensitive, thus small differences in concentrations of those "other" compounds do not have a significant effect on the measurement at our level of accuracy.

Every equation assumes some sort of balance between consumed sugar and produced ethanol. If the equation does not work precisely that simply means that particular beer does not follow the assumed balance. The balance can be theoretical or experimentally build in the equation - but it is always there. That is something that Balling figured it out in 1865 since then his equation is kind of golden standard although deviations from his balance/equation are known.