Thanks David for weighting the grapes vs stems. That’s cool to know it’s 2.2% of the weight. If I see a grape cluster from another producer at the facility where I produce at, I will do the same and report back the two weights.
Andrew (Briceland Vineyards) you might be right. I simply don’t know nor am trying to be a know it all here so any experiences are welcome!
With regards to maybe there being water in the stem, Bohan vineyard is dry farmed and the stems are dry as a bone and yet the conversion at Bohan is often super low, making for super low alcohol wines (with stems). So here I am again with more questions based on experimental answers.
I should point out so there isn’t confusion to posting the lab analysis that the remaining sugar at bottling will be ZERO. The remaining sugar will be converted to alcohol in the barrel. These wines are stable with natural acidity and healthy wines go to zero (most of the time). Alcohol bombs which are unstable (meaning with high pH and low TA (Total Acidity) more often get stuck with remaining gluc/fruc and that remaining sugar means getting out the sterile filter to filter the wine so it doesn’t go off in the bottle. The wine ends up with gluc/fruc remaing and often tastes sweet and hot and flabby.
Another note: It’s my opinion that de-stemmed wines do NOT taste more intense than whole cluster wines when all variables are identical for my own taste. For me, the intensity is equal between both fermentations. Once again though, this thought is subjective.
Quick question - did you send off for.starting sugars, etc for both fermenters? There may have been a significant difference in your starting numbers - I’ve certainly seen that.
I have to believe someone at Davis or Fresno knows the answer to this, it’s probably in a text book somewhere. If not, might make a good senior project.
Larry, no we didn’t but as I mentioned, the material is the same, the exposure is the same and we used an anton par to measure sugars and starting brix which were the same in each tank.
I understand why you are asking but there was no difference in sugars at the onset nor in overall ripeness from vine rows / sections of the vineyard.
As for pH, no, I did not run pH nor TA from ETS laboratory pre nor post ferment. I really don’t use either number to be perfectly frank. I know or at least like to feel like I know where the chemistry is via taste and put less reading into the numbers. I have picked at 19.5 brix and picked at 25 brix and am more keen on the calendar, the weather and overall vintage characteristics (drought, wet, etc).
We do run pH at the winery and this the only data I have:
On 08/20 pH was 3.33 pH. We picked during the night time of 08/21 so there was 1 additional day of ripening from our pH of 3.33
The fruit landed in tank on 08/21.
On 08/24 the pH was 3.5 in tank.
With at least my fermentations and with stems, I often see pH go up during the fermentation and then go back down towards the end of ferment. That topic though deserves it’s own thread.
Thanks for the replies. Did you run Anton Paar numbers throughout fermentation? Especially for the first 2-4 days after arriving? I understand what you are saying, but I rarely if ever see two fermenters having identical sugar levels, even qhen the fruit is 'identical '.
Larry, that’s all the data I have. I too rarely see fermentation’s that end at the same alcohol level. That said, I can’t say that I have ever seen a 1 degree difference from the identical starting point.
Maybe, maybe not. I’d expect the wine industry to have documented individual variation in perception of TCA in wine at least as well as the variation in perception of PROP has been documented in purely academic tasting studies. Where are we on that? If the wine industry does not find TCA worthy of serious research funding, would (did) they bother with something as esoteric as this?
A few of thoughts…mostly from trying to build a mental model around these results. First, we know that yeast and especially native yeasts are not monolithic in nature (in terms of character) and various strains will ferment to certain alcohol tolerances. (With particular strains taking over or becoming more dominant as the conditions change throughout ferment.) Temperature and oxygen undoubtedly have an impact on the general health of yeasts through fermentation as well, along with PH. Lastly, my limited understanding is that yeasts do not produce alcohol at the same efficiency as one another, particularly for non-lab produced yeasts. (Seeing as lab yeasts are often chosen for reliability).
Putting those things together, I wonder if the whole stem ferments, through lower temps and more structure between berries (or some other factor), allows for particular strains (particularly less alcohol tolerant ones) to remain healthier and/or more active throughout fermentation, with these yeasts potentially producing alcohol less efficiently per available sugar. Thus in general, leading to a more complex fermentation with more alcohol/temp sensitive yeasts remaining viable longer, and more vigorous yeasts being buffered by a larger, more competitive culture. (Or perhaps the stems themselves are introducing a greater quantity or complexity of indigenous yeasts).
Certainly a lot to unpack here…but at the end of the day it seems like we should be asking how stems impact yeasts as these are the only mechanism for producing alcohol.
Also, w know s. cerevisiae don’t particularly like living on grape skins, as they measure about one millionth the microbial population there. We know they like living in woody environments, notably oak bark. We also know the microbial population on the grape skins is ever changing as the condition of the grapes and weather change, altering their competitive environment. So, I haven’t seen any studies, but we should expect a different microbial population on the stems. Then also, are there any nutrients or enzymes that come with them stems that could alter fermentation dynamics?
I’ve spent a fair amt of time on the ‘where can brix go’ question (there’s a “where’s Waldo”, or a “wack a mole” joke here somewhere I’m sure). It’s 3am (fell asleep in front of the TV), so don’t expect it to be too coherent.
The possible paths for sugar:
There was more or less than you thought: getting a really accurate brix number (in vineyard, in tank, etc) is really hard…and is impossible if some portion is whole cluster or whole berry. Even without WC or WB, it’s still really hard, and involves doing things in the name of brix accuracy rather than good winemaking…Jamie’s in the latter camp of course.
The sugar gets converted to Ethanol that either ends up in the bottle, or evaporates (esp during fermentation, esp open top tanks), or the Ethanol gets converted into some other compound. This last option is almost always undesirable except in very small quantities, ‘higher’ alcohols for example, which can sometimes be interesting in very small quantities…but most times they make a wine ‘interesting’ or worse, rather than truly interesting.
The sugar ends up in the bottle as rs (in the same form of sugar that was in the grape)
The sugar gets converted into some other compound, glycerol is a popular option here. Side comment: converting sugar to ethanol is stressful on the yeast…producing glycerol is the yeast’s way of relieving that stress (some yeast are better or worse at handling that stress and produce less or more glycerol). Glycerol isn’t the only option here tho…here are many compounds that the yeast can turn the sugar into. The common factor to all those options (including glycerol) is they all taste sweet (in varying degrees , but all sweet). There are various new ‘low alc’ yeast that are appearing on the market…they’re all in this category.
One thing that can reduce the sweet compound created in the last point (producing glycerol et al) is to have some organism in the wine that feeds on the compound as an energy source. This is massively risky of course…the one situation that can be relatively/sometimes safe is ‘Sous Voile’ aging in barrel. Sous Voile is french for ‘under a veil’, referring to the film yeast that can form on top of a wine. These yeast need a carbon source (e.g. sugar/etc) to feed on to grow/live…and glycerol is it. Voila…less glycerol and less sweetness…sweet! Other than that, this point is all danger (Sous Voile can be safe, but has stylistic implications…often excellent tho). Note: I make a Sous Voile Chardonnay.
High Tech machines: There are high tech machines that will remove and/or change a surprising variety of compounds in wine, including ethanol. Nuff said imo.
Those are the only games in town for the grape sugar (it’s 3am, so I might have forgotten a minor point, if so will add, but won’t change my thoughts…thoughts I’ve churned through for years). For me, the best option is to turn the sugar into ethanol and keep it that way…and to pick at a lower brix if I want less of it. Anything else involves some sort of sweetness, which I hate, or something undesirable.
This is just a wild guess, but one possibility is the final alc difference is mostly due to the tanks having somewhat different brix levels, and non-stem was hotter and blew off more alc (can be a significant source of alc loss).
It’s my understanding that glycerol is mostly determined by the yeast strain, and I’d guess/assume they were both the same strain.
Ah, flipped that around. There’s also an observation/theory that stems absorb some amount of alcohol that gets tossed in the bin after pressing. Not sure that would account for that much alc tho.
Perhaps having stems in the tank changes the fermentation/tank ‘dynamics’ that allows it to blow off alcohol at a lower temp, i.e. if the stems provide a ‘channel’ for the alc to more easily get through the cap and evaporate away. I’ve never heard anyone claim this before…tho there are comments that stems lead to a cooler ferment for similar reasons as this.
