Effect of gross lees on brix/SG

[BarrelMonkey]

My 2024 Pinot Noir is nearing the end of its fermentation, and I thought I'd pass on this observation which was a new one for me. My two 44 gal fermenters with RC212 have fermented vigorously; my native yeast experiment in a third fermenter was of course slower to get going but has caught up, and all seemed well, except...

Things seem to have stalled out around 0.2 brix (1.0008 for those of you who work in SG). Here is my fermentation profile (#1 and #2 RC212, #3 native):



Based on prior experience I would expect -1 to -1.5 brix for absolutely dry wine. However, it sure tasted dry (and good!) and the cap has dropped, leading me to think fermentation was over.
One thing I noticed was that there was an unusually large amount of white flocculent sediment in my sample jar:



This photo was taken only a minute or so after filling the sample cylinder, and as you can see it's already settling out. So I took a larger sample and left it to settle for 30 minutes or so, after which I decanted it and retested brix. This time it was -1.1, much more in line with expectations. It seems like that white fluffy stuff (yeast? fruit pulp?) was buoying up the hydrometer and giving me a falsely high reading. Curious as to whether others have experienced this?

 

[mainshipfred]

I can only imagine the solids would have an affect on the reading. I'm surprised it's not more.

 

[Ohio Bob]

Curious as to whether others have experienced this?

Yes. It’s why I highly recommend getting a refractometer. You only need a few drops so I give the must a good stir, then drop a few drops onto the refractometer. It’s less accurate once alcohol generation starts, but good enough to know when to add nutrients at the 1/3 sugar depletion point, or when to press.

 

[winemaker81]

An important point to remember is that SG is a measure of the relative density of a liquid with respect to distilled water. It is not a measure of sugar, or any other constituent. Just density.

To be totally honest, I've understood this only in the last year or so.

Thinking in brix after fermentation starts leads towards a misunderstanding of what is being measured, e.g., thinking in terms of -1.0 to -1.5 brix is totally wrong. Red wines tend to have a higher FG than whites simply because there is more "stuff" in the wine, raising the SG.

Note that I'm not disagreeing with @Ohio Bob -- it appears he's using a refractometer as a relative indicator.

 

[BarrelMonkey]

An important point to remember is that SG is a measure of the relative density of a liquid with respect to distilled water. It is not a measure of sugar, or any other constituent. Just density.

Understood, yes it's just density. That being said, sugar is the major contributor (in clean juice at least) so brix/SG is a good surrogate for what's going on. I've just never seen such a dramatic difference based on the non-sugar solids in a sample. At the winery where I work we've probably had 20+ different pinot noir fermentations this year, and in almost all cases they'll get down to between -1.0 to -1.5 brix.

I think the key here is that the brix/SG measurement is only one piece of data to consider. The observation that (a) the cap softened and dropped, (b) the wine tasted dry and (c) that white stuff seemed unusual, all led me to re-test a settled sample and conclude that primary fermentation was complete. I think that's the best we can do short of sending a sample to a lab for glu-fru testing.

Onward and upward! We drain/press out tomorrow...