Skewed ABV Reading due to lactose addition... Help!

[mcognv]

Hey guys, first post, long time watcher. I brewed a 12 g batch of Chocolate Mint Stout during Learn to Homebrew Day, and kegged 5.5 g the other day to make sure it was ready for Thanksgiving tomorrow, and also to make sure the peppermint extract wasnt overwhelming in the bottles, so the keg was done first to sort of fine tune it. It was a bit dry for what i was trying to go for, so I added an extra 1 lb of lactose to the keg (the 12 g recipe I added 2 lb to the boil), and it tastes excellent now, and I'm very happy with it. Problem is, I didnt take my final gravity measurement before adding the extra lactose, and now my measurements are way out of whack. The inital reading was 11.5 Brix (my refractometer only has Brix) and now the reading is 10.5, which is something like 1% ABV, which isnt the case I know!How can I figure out what to tell my party attendees what the ABV is?

 

[Yooper]

Hey guys, first post, long time watcher. I brewed a 12 g batch of Chocolate Mint Stout during Learn to Homebrew Day, and kegged 5.5 g the other day to make sure it was ready for Thanksgiving tomorrow, and also to make sure the peppermint extract wasnt overwhelming in the bottles, so the keg was done first to sort of fine tune it. It was a bit dry for what i was trying to go for, so I added an extra 1 lb of lactose to the keg (the 12 g recipe I added 2 lb to the boil), and it tastes excellent now, and I'm very happy with it. Problem is, I didnt take my final gravity measurement before adding the extra lactose, and now my measurements are way out of whack. The inital reading was 11.5 Brix (my refractometer only has Brix) and now the reading is 10.5, which is something like 1% ABV, which isnt the case I know!How can I figure out what to tell my party attendees what the ABV is?

Let's see- lactose would add about 6 SG points to 5.5 gallons, so that's not really very much and could be considered negligible. The thing is, the refractometer reading of 10.5 is useless, as it doesn't account for alcohol in the mix which skews the reading after fermentation starts. . If you take a hydrometer reading, and subtract 6 points, you'd have your actual FG and can easily calculate it from that.

 

[Calder]

Your message is a little confusing (too much going on). Personally I don't trust refrractometer readings after OG, but lets see if I can figure it out.

The OG of your 12 gallon batch was 11.5 Brix. Per my calculator, that would mean an OG of 1.048. This might be slightly off as I have the calculator corrected for my refractometer readings, but it is close.

You kegged 5.5 gallons of this, and added 1 lb of lactose to this 5.5 gallons of beer while in the keg. Then you took a gravity reading and got 10.5 brix.

As Yooper said, 1 lb of lactose would increase gravity by ~.006 in 5.5 gallons.

To use the brix scale correctly, we need to add this .006 to the OG. So the effective OG is 1.048 + .006 = 1.054.

If we then use the 1.054 OG and a final reading of 10.5 Brix we get a final gravity of 1.034, or an abv of 2.7%.

Maybe someone else can come up with other numbers. That seems a very low attenuation, even with 2 lbs of lactose in there. You should probably take an hydrometer reading to make sure.

 

[ajdelange]

Refractometers are pretty useless in brewing unless calibrated against another instrument. I think probably the best you can do here is to assume that you made the beer without the lactose and compute the estimated OG from that using whatever you typically experience as an efficiency number. Then compute the estimated FG from the middle of the yeast's specified attenuation capabilities (e.g. if the yeast is labeled as doing 70 - 80% ADF use 75%). Then calculate ABV from that. The lactose is being completely ignored because it doesn't ferment either when you added it to the wort or the finished beer. This is going to be a fairly rough estimate but probably good to ± 1%. It is certainly better than anything you will estimate from refractometer readings.

The only way to be sure, of course, is to send a sample off for analysis. I think White Labs is now offering that service for a price that isn't too bad.

 

[Calder]

Then compute the estimated FG from the middle of the yeast's specified attenuation capabilities (e.g. if the yeast is labeled as doing 70 - 80% ADF use 75%). Then calculate ABV from that. The lactose is being completely ignored because it doesn't ferment either when you added it to the wort or the finished beer. This is going to be a fairly rough estimate but probably good to ± 1%. It is certainly better than anything you will estimate from refractometer readings.

The only way to be sure, of course, is to send a sample off for analysis. I think White Labs is now offering that service for a price that isn't too bad.

I couldn't resist replying. You say to estimate attenuation based on published data of +/-5%, then say the result should be within +/-1%. The +/- attenuation is based on a specific set of conditions, which he doesn't have.

He could also have a stuck fermentation, be using a lot of unfermentable specialty malts, mashed high, or other issue, which could drive any estimation of FG and ABV way off.

His OG reading in Brix is pretty good, and all he has to do is take an hydrometer reading to get a good assessment of where the beer is - no lab required!

 

[ajdelange]

I couldn't resist replying. You say to estimate attenuation based on published data of +/-5%, then say the result should be within +/-1%.

Intuition tells us that the answer is about 4%. To see this it may help to look at some numbers. Assume he mashed 15 lbs of grain and then added 2 lbs of lactose. If his overall mash efficiency was 65 - 75% he'd have 9.75 - 11.25 lbs extract from the grain plus the two pounds lactose would give 11.75 - 13.25 lbs total extract over 12 gallons beer means 0.979 - 1.105 pounds of extract per gallon which implies 11.24 - 12.62 °P as the observed OG of the wort. Note that this range includes his observed reading but that was taken with a refractometer and refractometers are quite unreliable in their mapping to OG. Yes, they often give a result which is pretty close but often don't. I've seen them off by at least 1 Bx and sometimes more.

Now we know the lactose doesn't ferment so we simply don't count it. The extract absent the lactose is from 0.812 - 0.938 pounds/gal corresponding to an OG range of 9.39 - 10.79 °P.

Now we look at yeast performance. The typical range of ADF for a yeast is 70 -80%. The minimum AE we would expect is 0.2*9.39 = 1.89 and the maximum .3*10.79 = 3.24 which means we'd expect a difference of at most 0.3*10.79 - 0.2*9.39 = 1.359 °P in the apparent attenuations. As the Balling factor is about 0.415 the range of estimated ABW's would be 0.415 times this or 0.564% which translates to an ABV span of 0.71%. This is less than 1 % ABV and that is what I meant when I said he ought to be able to estimate ABV to better than a percent. Assuming that he hits in the middle of the estimated efficiency and ADF he'd have close to 10°P fermentable wort and with 75% attenuation he'd have a drop of 7.5 °P which, with Balling factor 0.415 for 10°P would give him ABW 3.11% and ABV 3.93% (as I said at the outset intuition tells us the answer is about 4%).

The +/- attenuation is based on a specific set of conditions, which he doesn't have.

They can't be too specific or they wouldn't span 10% ADF.

He could also have a stuck fermentation, be using a lot of unfermentable specialty malts, mashed high, or other issue, which could drive any estimation of FG and ABV way off.

Sure, he could but he probably doesn't. If he isn't going to take proper measurements then the best he can hope for is an estimate.

The fact that he found the beer too dry suggests that he had a complete fermentation. With a stuck fermentation the beer would have been too sweet - not too dry.

His OG reading in Brix is pretty good,

No, it isn't as, in the first place, it was made with a refractometer and in the second place a hydrometer reading doesn't really give the OG as the OG really isn't actually defined. Is it as measured in the kettle, or in the fermenter (does it include starters?) and does it account for water lost by evaporation during fermentation, for example. Professionals actually determine OG by measuring ABV and back calculating the effective OG though they do, of course, measure SG of wort at various points throughout the process.

..and all he has to do is take an hydrometer reading to get a good assessment of where the beer is - no lab required!

He can, of course, do that but he won't get a good assessment - probably no better than the WAG estimate I gave above. FWIW I usually find about 0.3% difference between calculated and measured ABV using the Balling formula and very accurate gravity measurements. Most home brewers seem to be happy with ±1% knowledge though I think a lot of them fancy that they are getting more accurate results than that. Not likely with the formulas most of them use which don't take Balling factor into account.

 

[Calder]

Bull ......!

 

[ajdelange]

As it's all basic brewing science it's clear that you are not familiar with same. If you just tell me which parts you don't understand I can try to explain them to you. It's never wise to advertise one's ignorance in a public forum. A blanket dismissal of material found in any brewing text does that. Conversely saying that you are unclear on, for example, Balling factor, does not.

 

[day_trippr]

"Popcorn! Stat!"

Cheers!

 

[ajdelange]

Thinking a bit more about the OP's question makes it clear that there is a lot of uncertainty here and when that is the case a Monte Carlo approach is often beneficial. I took the calculations I posted in #4 and ran through them 10,000 times (obviously I used a computer) using a different combination of ADF and efficiency each time assuming that 15 lbs of grain was mashed. I had hoped OP would respond telling us how much grain he did use so I could refine the estimates a bit but he didn't. In any case I assumed efficiencies were normally distributed with a mean of 65% and standard deviation of 5% i.e ~ 68% of the efficiencies fell between 60 and 70% and 95.4% of them between 55 and 75% but no efficiencies greater than 80% were used, Similarly for ADF I used a mean of 76% and standard deviation of 54%. No ADF greater than 82% was allowed but there was no lower limitation.

The histogram below shows the relative number of computations that resulted in the ABVs on the horizontal axis. As expected from the reasoning in #4 most came out near 4%. The 'probability' of finding the ABV in a particular range is the area under the curve in that range. Thus OP can tell his guests: 'The ABV of this beer is between 3.5 and 4.5% with 84% probability' or 'The ABV of this beer is between 3.8 and 4.2% with 42% probability.'

To OP: If you really used 16 lbs of grain rather than 15 just scale ABV up by 16/15 = 6.7% i.e. slide the histogram to the right by that much. The mean of the histogrammed values is 3.95%. If you used 16 lbs it would be 3.95*16/15 = 4.21%. If you used 14 lbs then 3.95*15/16 = 3.70%. It's not really quite linear put pretty close.

 

[mcognv]

Wow! I didn't think anyone would reply, but everyone was so very helpful, thank you all for the responses!

Contrary to what AJ is saying, I will announce that I am very ignorant to a majority of the science you are throwing out. I did have a hydrometer once upon a time, but got the refractometer as a birthday present upgrade and passed down the hydrometer to my gf's dad who does wine.I wish my refractometer gave SG but i guess it was the cheap one, and only shows Brix. The craft brewery down the street only ever used Brix himself, and had a table to the conversion to SG, so I figured if he was using it, it must be good.

Anyways, it was designed to be a 15 gallon batch, but i lost a few gallons, most in the mash because I didnt put a book or something on one side to get all of the runnings possible. I was going for 8.6% and let beersmith do the rest of the work, and ended with

41lb Pale Malt
2.5of ech Crystal 40, Crystal 60, and Chocolate Malts

 

[ajdelange]

Contrary to what AJ is saying, I will announce that I am very ignorant to a majority of the science you are throwing out.

Many home brewers enjoy the hobby without learning a scrap of brewing science and that is fine but what happens in the process of beer making is nonetheless ruled by the science and that if one wants to fully understand what is going on he must often turn to the science for the answers. Also keep in mind that, with reference to the remark about the basic science being in any brewing textbook that NCJHB isn't a textbook. Also the Monte Carlo stuff isn't found in brewing textbooks. It's just a general technique for solving problems with lots of uncertainty.

I did have a hydrometer once upon a time, but got the refractometer as a birthday present upgrade and passed down the hydrometer to my gf's dad who does wine.

A mistake. Get another one.

I wish my refractometer gave SG but i guess it was the cheap one, and only shows Brix.

A better one is likely to show RI (refractive index). Refractometers come from the sugar industry and they work mostly in Brix and RI. The brewing industry works in ° Plato (essentially the same as Brix) and specific gravity.

The craft brewery down the street only ever used Brix himself, and had a table to the conversion to SG, so I figured if he was using it, it must be good.

The limitations of refractometers in brewing have been widely discussed over the years on HBT and elsewhere. To convert from Brix to SG multiply the Bx reading by 4, divide by 1000 and add 1 thus 10 Bx ~ 1.040 SG.

Anyways, it was designed to be a 15 gallon batch, but i lost a few gallons, most in the mash because I didnt put a book or something on one side to get all of the runnings possible. I was going for 8.6% and let beersmith do the rest of the work, and ended with

41lb Pale Malt
2.5of ech Crystal 40, Crystal 60, and Chocolate Malts

The 41 lbs of pale malt would give you about 0.7*41 = 28.7 lbs of extract. The 7.5 lbs of specialties would perhaps yield 4 lbs of extract for a total of 32.7. If you produce 15 gallons of beer from that your extract will be 32.7/15 = 2.18 lbs/gallon. That corresponds to OG of 23.9 °P (SG 1.1005). The fact that you measured less than half that says that you had terrible efficiency or lost a lot of extract in what was left behind etc. At this point about all you can do is rely on the refractometer reading and hope that it was reasonably accurate. It is in the majority of cases.

 

[bracehelton]

This is the simple solution:
Friend: Hey man, what's the ABV on this?
You: Bout 4.5 to 5%
Friend: Cool BRO!
You: Yup (internal thought: note to self, next time buy a good hydrometer and take proper gravity readings...)

Solved. Nonetheless, that was some pretty slick stuff AJ!