Conversion Rates for whites fermented in barrel

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Joe Webb
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Conversion Rates for whites fermented in barrel

#1 Post by Joe Webb » April 3rd, 2016, 2:33 pm

A couple weeks back on a thread about Semillon there was some discussion about conversion rates for fermentation of whites. I have been asking around again to fellow winemakers and have found quite a bit of variation. I am interested in what y'all are seeing and any winemaking things you do that could change what you see.

I harvest my SaviB and Semillon early in the am get them to the wooden slatted basket press whole cluster with some rice hulls. I press off about 120-130 gal/ton to tank. I settle overnight and go to barrel (66-100%) and stainless drum (0-33%) the next day. I send samples for brix and flu/fru to ets post racking to barrel. Brix at harvest for my SB ranges from 20.5-21.5, and Semillion 20-21. pH range is 3-3.2. All my ferments are native with no additives except so2 post ml competition.

My average conversion rate based on brix for SB is .623 with a range of .59-.69.
My average conversion rate based on brix for for Semillon is .636 with a range of .62-.66.
It sounds like I am on the higher side for whites and lower side for my Pinot Noir, average .57 range of .55-.59.
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Ed Kurtzman
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Conversion Rates for whites fermented in barrel

#2 Post by Ed Kurtzman » April 3rd, 2016, 3:03 pm

A 0.69% conversion rate is the highest I've ever heard. I can't remember if ETS does their brix measurement by refractometer? If they do, I would always add 1 brix to get the equivalent brix via hydrometer. In my experience, they're always 1 brix apart. I usually range between a 0.57 and 0.61 conversion rate based on hydrometer readings, higher with refrac. readings. Definitely on the higher end for whites, but no higher than 0.61. Maybe the cooler and more closed containers for white fermentations does hold in more alcohol than the hotter and more open containers for red?

I heard an idea once that natives will lead to higher conversions because there's a smaller population of yeast during the growth phase when glucose is being consumed but not fermented into alcohol. Since the smaller population eats less glucose to start, that leaves more glu/fru for the yeast to ferment during the fermentation phase, leading to higher alcohols in natives. I've never done any side by side experiments to see if this is true, but it sounded plausible when I heard it, 21 years ago.

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Joe Webb
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Conversion Rates for whites fermented in barrel

#3 Post by Joe Webb » April 3rd, 2016, 4:04 pm

My ETS reports don't state how they measure but I only send a small 60 ml sample so I doubt its hydrometer. That .69 conversion was in 2010 on my SB it definitely was a big surprise to me when I got the final ETOH. In 2010 my semillon had its highest conversion rate to at .66, so maybe a vintage anomaly. It looks like with out that vintage the rage for SB for me is .59-.62 much more in line with what you mention. I have been the last few vintages looking at conversion for brix and glu/fru with the glu/fru conversions lower by .02-.03 on the rates.

All my Pinot Noir is open top and peak temps for a day are usually low to mid 90's so I am sure some ETOH will blow off those where it would not with the white less what little makes it out of the airlock.
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John Oglesby
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Conversion Rates for whites fermented in barrel

#4 Post by John Oglesby » April 6th, 2016, 6:38 pm

I'd imagine ETS uses a refrac for brix. Hydrometry with a lab of that volume would create a bottleneck production wise.

0.62 is what I find to be the norm for conversions across both barrel fermented whites and tank fermented reds. Whether it's the absorption of the blown off EtOH back into the juice or its the hydration of shriveled berries releasing more sugars post cold soak/innoculation.
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Conversion Rates for whites fermented in barrel

#5 Post by ericleehall » April 7th, 2016, 12:54 pm

From the ETS Website:

The ethanol by densitometry measurement is to be used for determination of alcohol on distillates and for assigning values to ethanol/water mixtures used in association with calibration of instruments such as the Anton Paar Alcolyzer.
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