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Noticing Lower Brix > Alc Conversions in 2016-18

Posted: March 4th, 2019, 9:07 pm
by Roy Piper
Anyone else noticing lower conversions from brix to final alcohol lately? The last three years I find it has gone from .59-.60 to >.55-.57. That is up to 0.5% lower alcohol. Curious if other noticed this too.

Re: Noticing Lower Brix > Alc Conversions in 2016-18

Posted: March 14th, 2019, 7:39 am
by BenjaminL
Hey Roy, I think the horse is out of the barn trying to use Brix to forecast alcohol. Glucose/fructose content is a much more accurate predictor, Potential Alcohol (% vol) = glucose + fructose (g/L) / 16.83.
I think you are right noticing vintage variation in alcohol conversion due to differences in Glu/Fru: Brix ratios. Please look at this chart from ETS Labs out in Napa:
https://www.guildsomm.com/resized-image ... atio-2.jpg
it shows that even between cultivars there are large differences in Glu/Fru: Brix ratios. I'm still looking at this chart to try to find patterns, but its not easy.

Re: Noticing Lower Brix > Alc Conversions in 2016-18

Posted: March 14th, 2019, 11:04 pm
by Eric Lundblad
Brix is a fine measure for predicting alcohol, but you need to centrifuge your samples before testing. The real issue is getting a juice sample that's truly representative if your tank as a whole, a difficult thing to do with precision. And predicting the specific details of your fermentation can be tricky...the amount of non-Sacc C yeast fermenting, the amount of alcohol that blows off during the heat of fermentation, and other related issues.

But, at the end of the day, the amount of alcohol that a Sacc C yeast produces from a fixed amt of sugar as input to the yeast is pretty fixed.

Re: Noticing Lower Brix > Alc Conversions in 2016-18

Posted: March 21st, 2019, 9:50 am
by larry schaffer
Interesting - took part in a seminar yesterday where they were finding the opposite down here - higher conversion factors rather than lower. Could have been 'user error' in getting accurate starting figures for sure but interesting indeed.

Many wineries do not send off initial samples for glue/fruc and depend upon brix numbers either from a refrac, a densiomenter or hydrometers. I've been using a DMA Densiometer for quite some time and am quite happy - and it's given me pretty consistent results thus far . . . but we are all oftentimes surprised at alcohol levels after fermentation . . .

Cheers!

Re: Noticing Lower Brix > Alc Conversions in 2016-18

Posted: March 22nd, 2019, 8:38 pm
by John Oglesby
I haven't noticed a difference. I still see conversation rates in the .62 range for the last few harvests.

Using G/F as a predictor for alcohol works about as accurate as a brix measurement. It's still a floating number throughout fermentation so to say what your true starting point is rather misleading. Its "in the ballpark" so to speak.