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Messages - Petr

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1
Thanks.  Sorry to drag this back up.  (The optical does function usefully in the mash, though, but only when I create a specific correction factor for each batch.  I suppose that supports your assessment of its accuracy.)

No problem. I guess it does support that. Wort correction factor should be characteristic of the instrument, not each batch.

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An optical hand type, although I have a digital one on order (I really do find refractometers handy in the mash, and this should simplify my brewing.)  Again, don't really need it post boil, just curious.

Try that new one once you'll get it. I'm pretty sure you'll get much better results. I suspect that your refractometer is faulty such great deviation is simply not physically possible if the instrument and its use is ok.

3
Don't want to get back into the weeds, just curious if anyone else who was having seriously questionable results with refractometer has seen improvement.  Tried it for kicks again last two batches.  During fermentation with actual saccharometer readings of 4.1°P and 4.5°P respectively, ALL the calculators gave results <0, so I didn't even bother when a batch finished out at 3.0°P.  Still use refractometer during mash, just still doesn't work for me in ferment.

I think that the answer for you if you're getting less then 0 as a result, is unfortunately simple. You're either using wrongly the calculators or your refractometer does not work as it is supposed to. What kind of refractometer do you have?

4
I certainly defer to you, Petr.  I got into this discussion because I was curious as to why this didn't seem to work for me:  or at least only occasionally worked.  I may have misinterpreted some of what I read, or the writers did.  It seems many of us get higher FG readings with hydrometer than any of the formulas predict.  As I said, I don't need a refractometer except pre-boil.  For those who do, I hope they find your formula serves their needs. It's astonishing how many times essentially this same conversation has been repeated on various forums.  It seems there is great interest in refractometers,  but a few intractable gremlins in the works! Carry on the good work.  BTW I appreciated your recent article on hop utilization, too.

Hear, hear. You know it depends on every one of us. I prefer the refractometer just because of the convenience of it – take few drops of wort and in a minute you have the reading, accurate enough for my purposes. In other cases as for low volume fermentation tests that I do for example for yeast hunting, it is even a necessity because I just can't afford the volume needed for the hydrometer. Glad you like the hop article!


5
On the flipside, what makes us think that density is a good measure of how the beer will taste?  It is well known that different sugars taste vastly different in a finished beer, so one 1.015 beer can taste sweet and another not at all.  Add alcohol into the density equation and you aren't even measuring one thing, but a balance - hence "apparent attenuation".  So, other than knowing when your beer is done, what is it really telling you?

I've been measuring with refractometer only for a while, and it tells me just as much about the final mouthfeel of a beer as density ever did.  It also helps to measure a variety of beer (commercial, other homebrews) and get an idea of what your target is for the style.  It's like going from F to C: you're never going to make the switch if you're constantly doing conversions in your head.  Think native!

No one claims that. FG is more of the process variable – it tells you how is the fermentation going, if it is done, how yeast performed, consistency between batches etc. with a deeper insight you can dig out even more. For instance, if yeast fermented maltotriose. It has also limited informational value about the body but that has to be considered in the whole picture of the taste. Yes, you're not measuring the variable directly and you're right that it measures the balance but the balance is relatively well understood with good accuracy for our purposes, so there is not much of the problem in that. The understanding allows us to measure things undirectly but reliably.


6
Sorry, I didn't save my search results.  I just kept reading until I was assured there really is something going on here to confirm my suspicions.  I think all the non-alcohol factors, in the aggregate, can have enough impact that a formula based on one set of samples will not apply universally.  But if you are only interested in a certain margin of accuracy, I'm sure you can establish a correlation that works for you.  This really doesn't bother me, I just plan my brew length with a spare liter or so to allow for all the samples I might want to pull.  I realize this is not feasible for small batch brewers. I don't really have skin in this game. The amount of discrepancy between formulae,  each of which was empirically derived, just bothered me.  I wanted some insight.  Now everyone should just do what works for them!

Robert, you're wrong there. First of all, none of the formulae are based on one set of samples only. Non-alcohol factors (as hop compounds etc.) are significant for taste but because of their low concentration the effect on refractive index is negligible for our practical purposes and unless you'll provide me with an appropriate reference of otherwise I'll believe that I understand my professional field. You're chasing the wrong issue, as I said the real problem is that in some instances yeast is not necessary following precisely the same material balance glucose->ethanole + CO2 + biomass. Secondly, you're wrong that each of the formulas was just empirically derived. If you would take a look at that original reference that I provided you would see that there was a lot of insight into that formula and its form has a strong theoretical background. That is precisely the reason why my formula works for the whole fermentation and not just only for well-attenuated beer.

As you said everyone should use what works for them. I just provided another option for those who are interested. I have plenty of feedback that it works just fine for a lot, and there are fewer that has opposite experience and reasons for that are unclear to me even if I'm well aware of its limitations. I would love to find out reasons but that cannot do until I will really know details of each case with the actual data. My experience is that in the majority of cases it is due to misuse of the instrument or/and formulae or too high expectations about accuracy that just simply can't be better than 0.001-0.002 depending on particular circumstances.


7
I did some deep diving on the interewebs this weekend, mostly threads on other forums (many I never knew existed) and some of the sources they led to.  Turns out there's a good amount of research confirming my suspicions above about many factors confounding corrections.  It seems hops alone can have an effect nearly as significant as alcohol, as can different grists, let alone all the other compounds in beer.  Much more research would be needed if it's even possible to develop reliable corrections, and the pros aren't going to do it, they don't use refractometers. We're just trying to use an instrument to measure something it wasn't designed to measure. (No I don't have all the references, you've got Google if you care.)

This looked good to me on a limited number of samples, but the more I've racked up, it looks like none of these formulas really works, which now doesn't surprise me.  If I have all the formulas in front of me (and thanks to Big Monk, I do!) I can find one of the half dozen that's fairly close.  But that just means that there's a one in six chance I can squint really hard and pretend it looks like something's working, not that it is.

So for my part, I'm back to the position that refractometers are useful pre-boil only, and I establish a correction factor for each individual batch using the saccharometer OG.  Even Terrill has said (referenced somewhere in this thread) that if you actually want to know FG (or for that matter when to spund) you really need a hydrometer.

So finally, if you're of the school of "close enough is close enough, I  don't  really need to know," why do you need any instrument at all?

  When it stops bubbling, its done!

I highly doubt that hop compounds can have a comparable effect on refractive index as alcohol that is just not possible from the chemistry point of view when hop compounds are there in ppm level and alcohol in a couple of %. Can you provide me with a work that you were referring to? I did my google research but didn't find anything close to that statement.

I'm normally just fine with +- 0.002 accuracy of FG, and for a long time now I use refractometer only. The main reason why I bothered with the new formula wasn't actually FG because for that purpose with reasonable accuracy you can use Terill's formula just fine. The reason was that sometimes I need also a reading during fermentation and don't want to waste about 100 mL of wort every time, especially if it is an experimental brew with total volume 2 litres and often less... The thing is that my formula works for wort during the whole fermentation and that is the main advantage of it. I know that not everyone is in need of measurements during fermentation but the option is there for those who need or/and want.

If you don't care about the FG at all then well no problem with that neither. It's up to every one of us.


8
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.

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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. 


10
I was already aware of the degradation of iso-alpha through Malowicki's work, but I was pleased to see the additional reference in that article from the IBD journal that confirms it. My upcoming article on Wort Boiling covers that degradation.

As Robert says, boiling too hard or too long has some serious negative effects on beer.

Malowicki and Shellhammer did a great deal of work on that! Good for us.

11
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.   




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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.

13
Saving to check out later.

I really hate the way BeerSmith and BrewersFriend handles whirlpool additions, but without an english publication it'll be hard for me to trust this guy. Especially considering his refractometer correction formula

It was published in a new issue of Zumurgy, so now you can read it in English. I'm the guy. What is the problem with my refractometer correction? It works great for everyone so far, much better than Terrils's one and giving the same numbers as BeerSmith's tool...

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