Over attenuation, Vikeman, get in here also.

[deuc224]

So Ive been dealing with over attenuation for a while and its becoming a serious problem. I use brewfather and go by their yeast pitching rates and they end up going WAY over. Here is an example:

SMaSH beer- 10.5 lbs of breiss 2 row, Amarillo 0.5 oz at 20 min left of the boil.
Boiled for 60 mins at 156, hand sparged and boiled for 50 mins cuz i hit my target volume sooner than expected.
Used 1/2 tsp of wyeast nutrient at last 10 mins, transferred to fermenter and used a 0.9L yeast starter with white labs 001 yeast.
Got a brix of 13.6=1.055 OG
FG was brix of 6.8=1.024

With the refractometer correction it says im at 5.91% alcohol, i was aiming for 5.02
Same thing happened to a chocolate stout i was brewing, I was aiming for 5.3% and with refractometer correction i shot at a 6.71%.

Im just starting to think that when it gets closer to FG should I just cold crash the beer to sleep all the yeast? These beers are finishing in 3 days, so basically i would be crashing at the end of day 2. Thanks all for the experience and help.

 

[Miraculix]

First of all, ditch the yeast nutrients, they are not necessary, especially not if you already have high attenuation problems.

Second, ditch the refractometer for fg measurement. You can use all the correction you want, it will be still just a ballpark number, at best. Validate the number with a calibrated hydrometer, that's the only way to be sure.

I'll bet after that, your problem will be gone.

You cannot stop a yeast with cold crashing. But anyway, stopping the yeast won't be necessary.

 

[deuc224]

You know what, ill take that advice. Ill do a beer this weekend and just use my hydrometer and no yeast nutrient..

 

[VikeMan]

With a typical wort correction factor of 1.04, a 13.6 brix refractometer reading is a 1.053 OG. And 6.8 "FG" adjusted for alcohol becomes 1.012 (using the Terrill formula).

And....with 100% Briess 2-Row, 60 minute mash at 156F, WLP001, and OG of 1.053, BrewCipher predicts an FG of 1.012.

I'd say you got about what you should have got, given your recipe and process. What FG were you expecting, and why?

 

[magno]

I agree with VikeMan and Miraculix above... Refractometer should not be used for FG readings, and if you are using one, your FG is as I would expect it to be.

I would say RDWHAHB and measure FG with a hydrometer.

 

[Snuffy]

Higher ABV? BONUS!

 

[Brooothru]

With a typical wort correction factor of 1.04, a 13.6 brix refractometer reading is a 1.053 OG. And 6.8 "FG" adjusted for alcohol becomes 1.012 (using the Terrill formula).

And....with 100% Briess 2-Row, 60 minute mash at 156F, WLP001, and OG of 1.053, BrewCipher predicts an FG of 1.012.

I'd say you got about what you should have got, given your recipe and process. What FG were you expecting, and why?

I've got to agree. I started using an optical refractometer several years ago. After hearing all the negative opinions here about how inaccurate they are for anything other than initial gravity readings regardless of formulaic ethanol computation corrections, I obtained a set of three narrow range hydrometers. Each of them were calibrated at 68F using distilled water, and each was spot on. For my next several brew sessions, measured at various stages from mash through final gravity readings (all corrected for temperature of the wort/beer), I did parallel readings with both the refractometer and the hydrometers. I could see no significant differences in either the (corrected) refractometer readings and the temperature adjusted hydrometer readings. The biggest area for misreading comes when fermentation is in progress when the refracted "line" on the refractometer is diffuse due to suspended particles in the sample on the platen. But the same could be said for cloudy wort in a sample jar and the need to 'interpolate' the actual graduated line where the meniscus intersects the hydrometer.

A week or so ago, Santa arrived early with a new electronic digital refractometer. Before it got wrapped it "needed" a 'quality control' check, so Santa allowed me to take a reading on a lager that was finishing up in the fermenter. The R.I. value displayed calculated out to an S.G. of 1.003 which was well below my predicted F.G. of 1.007 from a Fast Ferment Test. If anything, my FFTs are generally a point or two lower than the actual final gravity of the main beer, so this had me concerned for the accuracy of Santa's new toy. So I cross checked the refractive index of the automated device with my old handheld optical one. Exactly the same R.I., so of course the calculated F.G.s would be the same. I couldn't remember where I'd put my narrow range hydrometer set, and 'Santa' was getting tired of waiting to wrap the present, so I was unable to conclusively complete the experiment.

So, I guess my curiosity will not be satiated for another 11 days. But I'm somewhat confident that it will prove accurate. Unanswered however is the root cause of my apparent over-attenuation of the yeast in this lager fermentation (Wyeast #2105 - Rocky Mountain lager) with an O.G. Brix of 10.8. Obviously this will take some additional QC 'testing' to prove its accuracy.

 

[dmtaylor]

You can use a refractometer with great accuracy, but only after you understand the specific Wort Correction Factor for your particular instrument after numerous comparisons with hydrometer readings for different worts. People often use a WCF of 1.00 to 1.04, but it's not even always in that range. My WCF is definitely 0.99. So if I used 1.04 it would be pretty far off. I think you could be experiencing that in some fashion.

Other than that I agree with @VikeMan. Perhaps your FG and ABV goals are more the problem than the actual result.

 

[deuc224]

Thanks guys. I do calibrate it every time with distilled water before I put any wort on it. But ill take everyones advice on here. i guess im going blindly by what brewfather is telling me.

 

[Brooothru]

Thanks guys. I do calibrate it every time with distilled water before I put any wort on it. But ill take everyones advice on here. i guess im going blindly by what brewfather is telling me.

Recalibration is part of the "pre-flight" of my digital refractometer. Ensure the lens and well are clean, fill the well with steam-distilled water, turn on unit, verify displayed temperature readout of the unit and sample are within the range of the ATC, and then hit the automatic self-calibration. The readout should show zeroes.

Drain the well of distilled water, fill the well with the test sample and read the refractive index of the sample.

Calculate °Plato or specific gravity, applying the appropriate wort correction factor for maltose (refractive indices of brix refractometers measure glucose) which for my equipment has proven to be 1.04 as measured with a narrow range hydrometer.

Since the refractive indices of brix and ethanol are known values, it is logically possible to formulate a mathematical equation to infer an accurate measurement of specific gravity of the sample in which a portion of the brix has been fermented.

Brooo Brother

 

[VikeMan]

Calculate °Plato or specific gravity, applying the appropriate wort correction factor for maltose (refractive indices of brix refractometers measure glucose) which for my equipment has proven to be 1.04 as measured with a narrow range hydrometer.

They are actually designed to measure sucrose. Also, a good refractometer shouldn't really need any equipment related correction factor. It's the makeup of the wort sugars/dextrins that drive the need for the wort correction factor. The sneaky issue there is that different worts have different profiles. So when someone finds that a particular factor works best for them, it's usually because it fits their average/typical wort. IMO, any instrument specific driven differences in required WCF (for the same wort) simply indicate a not so great instrument.

I'm well aware that there are some web pages out there that talk about "instrument specific" WCFs as if that's why the WCF exists in the first place. I suspect these can all be traced to a 2012 blog post by Kai, where he in fact does talk about compensating for a cheap/faulty refractometer he owned.

 

[MikeCo]

You know what, ill take that advice. Ill do a beer this weekend and just use my hydrometer and no yeast nutrient..

Are you going to use both the refractometer and hydrometer and compare measurements?

 

[dmtaylor]

They are actually designed to measure sucrose. Also, a good refractometer shouldn't really need any equipment related correction factor. It's the makeup of the wort sugars/dextrins that drive the need for the wort correction factor. The sneaky issue there is that different worts have different profiles. So when someone finds that a particular factor works best for them, it's usually because it fits their average/typical wort. IMO, any instrument specific driven differences in required WCF (for the same wort) simply indicate a not so great instrument.

I'm well aware that there are some web pages out there that talk about "instrument specific" WCFs as if that's why the WCF exists in the first place. I suspect these can all be traced to a 2012 blog post by Kai, where he in fact does talk about compensating for a cheap/faulty refractometer he owned.

This makes sense, thanks for the insights. So it's a process and homebrewer-specific difference rather than a true equipment related difference. Cool, I can live with that. I know my process is very weird compared to others, which is probably why my 0.99 is so far off from "normal" people where it's 1.04.

Are you going to use both the refractometer and hydrometer and compare measurements?

Indeed, you really really should. It will help establish your own WCF as discussed.

 

[deuc224]

Also because the alcohol I was shooting for is easier to drink vs the 5.91. I guess I was looking for a more predictable result. Like the chocolate stout is the one that is freaking me out because of the 5.3 expectation when its a 6.71.

 

[deuc224]

Are you going to use both the refractometer and hydrometer and compare measurements?

Yeah, im gonna compare the two on the next cook which should be Saturday.

Also to you smarter people than me, how do I find the WCF of my instrument? Im using a Hanna digital 96811 if that helps. Im still gonna compare the two but just trying to streamline the process as much as possible. This has been an eye opener for me and a much appreciated lesson yall, I appreciate it a lot.

 

[VikeMan]

Also because the alcohol I was shooting for is easier to drink vs the 5.91.

So, if your OG was really ~ 1.053 (as I suspect it might have been), an FG of 1.012 would get you to about 5.4% ABV.

And even if the OG was 1.055 (i.e. a WCF of 1.0), the adjusted 6.8 final reading would be ~1.013, or about 5.5% or 5.6% ABV. Where do get 5.91 from?

 

[deuc224]

So, if your OG was really ~ 1.053 (as I suspect it might have been), an FG of 1.012 would get you to about 5.4% ABV.

And even if the OG was 1.055 (i.e. a WCF of 1.0), the adjusted 6.8 final reading would be ~1.013, or about 5.5% or 5.6% ABV. Where do get 5.91 from?

I got that estimation from brewers friend. starting brix was 13.6, and FG was 6.8. Brewers friend said it is a 5.91, 5.5% is much better and why was it that high?

 

[VikeMan]

I got that estimation from brewers friend. starting brix was 13.6, and FG was 6.8. Brewers friend said it is a 5.91, 5.5% is much better and why was it that high?

I'm not familiar with Brewers Friends' calculation, but my guess is that it's using a different adjustment for the presence of alcohol, and thus inferring a different FG for the same refractometer final reading.

If in doubt, verify with a hydrometer until you're comfortable with whatever formulae you're using.

 

[dmtaylor]

I'm not familiar with Brewers Friends' calculation, but my guess is that it's using a different adjustment for the presence of alcohol, and thus inferring a different FG for the same refractometer final reading.

If in doubt, verify with a hydrometer until you're comfortable with whatever formulae you're using.

Brewer's Friend uses the Petr Novotny formula for FG. Sean Terrill's formula will give you a different answer. I have spent many hours comparing 6 different formulas. My conclusion: Both Novotny and Terrill are useful. The accuracy of these two main formulas crosses over when FG is 1.014. Below 1.014, Terrill is slightly more accurate but Novotny is no slouch. Above 1.014, Novotny reigns supreme.

Regarding OG, everybody uses the same formula so it doesn't matter which website you use for OG.

To get your WCF, you need to measure OG on several batches using both a hydrometer and refractometer together. Only after a good 5 or 6 batches will you be able to understand your average WCF. Brewer's Friend has a tool on their site for figuring this out, see Part I of the following link:

https://www.brewersfriend.com/refractometer-calculator/
Then Part II becomes useful for calculating the FG after you understand the WCF for your personal brewing process. Many find 1.04 to be accurate. Others say 1.00. For my weird process, the WCF is 0.99. Only through experience and trial and error can you find the average WCF for your own process.

I provide far greater detail on how to do all of this here (rabbit hole alert):

https://www.homebrewersassociation.org/forum/index.php?topic=28544.msg404366#msg404366
Also... although they say refractometers have automatic temperature correction, I find that measurement varies significantly with temperature. Try to keep your calibration water and your wort at identical temperatures for the most accurate measurements. And whenever you use your refractometer, key: CALIBRATE CALIBRATE CALIBRATE! Garbage in, garbage out.

 

[VikeMan]

Regarding OG, everybody uses the same formula so it doesn't matter which website you use for OG.

Hopefully, they do! But it's worth noting that the default WCF, which affects the OG calc, may be different from tool to tool. So users need to be thinking about WCF even before they get to Part II.

 

[dmtaylor]

Hopefully, they do! But it's worth noting that the default WCF, which affects the OG calc, may be different from tool to tool. So users need to be thinking about WCF even before they get to Part II.

Indeed, very true. BF uses 1.00. Terrill uses 1.04. I have to change this every dang time I use one of their websites..... which I really don't use anyway since I have an Excel sheet that instantly gives me results for 5 different formulas and tracks and trends many batches so I can calculate an average deviation, etc. I'm a math nerd.

 

[Brooothru]

Hopefully, they do! But it's worth noting that the default WCF, which affects the OG calc, may be different from tool to tool. So users need to be thinking about WCF even before they get to Part II.

I think what you're saying is that a wort correction factor can be driven by equipment differences (also by temperature) but is also variable with the specific wort composition of sugars being measured (primarily glucose, maltose and maltotriose). That makes sense, since the wort is the final amalgam of the various sugars hydrolyzed from the different malts at different temperatures during the mash. Each of those variables makes up a very complex set of possible outcomes, thus potentially different wort correction factors.

What is unclear to me is how significant those variables are in the final calculation. If it's a +/-5% error, that would account for one person's observed WCF being 0.99 and another's being 1.04. If it's +/- 0.5%, then not a significant error in the realm of home brewing. I've read that the "average" (whatever that means) malt bill yields a mash that is comprised of 10~15% maltotriose, a much lesser amount of 'other sugars' (including glucose and fructose along with 'some' sucrose), but the vast majority of the available fermentable sugar is maltose. Sucrose and maltose have nearly the same molecular weight (342 g/mol), as opposed to maltotriose (504 g/mol), glucose (180 g/mol) and fructose (also 180 g/mol). Back of the napkin math would suggest that a wort with 15% maltotriose, 5% glucose/fructose/sucrose, and 80% maltose would have a molecular weight of 358.2 g/mol. Divide that weight by the molecular weight of sucrose (342 g/mol; the calibration media for a Brix refractometer) and you get 1.0473, or roughly a WCF of 1.04, variable with the amounts of maltotriose and other sugars in the wort. That's close enough for my computations, and I'd venture to say closer than my 71 year old eyes can discern the intersection of a meniscus on a hydrometer.

I haven't examined the math behind the computational formulae between Novotny and Terrill, and suffice to say I don't feel the least bit qualified to challenge either. But given @dmtaylor observations I may have to start using Terrill's model since most of my Final Gravities are well below 1.014. Either way, I'm quite comfortable relying on both my optical and digital refractometers to give me accurate measures of O.G and F.G when properly calibrated and appropriately calculated from observed refractive indices. In my experience they are at least as accurate as the measurements I get from a narrow range hydrometer, and much easier and less wasteful to use.

 

[VikeMan]

That's close enough for my computations, and I'd venture to say closer than my 71 year old eyes can discern the intersection of a meniscus on a hydrometer.

I almost mentioned this before, but that's yet another thing that can influence the "required" WCF, i.e. the WCF needed to agree (on avg) with hydrometer measurements. I can show a a picture of a hydrometer reading to several experienced brewers and get differing opinions on the value. Of course, this is "required" to match (potentially) a measurement error, and not necessarily reality.

 

[chipmunk]

Many find 1.04 to be accurate. Others say 1.00. For my weird process, the WCF is 0.99. Only through experience and trial and error can you find the average WCF for your own process.

I agree with this. I have a refractometer that I bought for maple syrup - I need a WCF of 0.92 for it to match my hydrometer readings! Once dialed in I find it quite reliable though.

 

[deuc224]

Man this is a lot to digest, but im up for it. Im loving all the info im receiving!