While I don’t often de-stem any of my Pinot Noir, this year we did. That said, I couldn’t help still fermenting a little fruit 100% whole cluster and I thought I would share the interesting finding.
We picked McDougall Ranch on Saturday, 08/22. Our rows have all the same exposure and the same clonal material and ripeness was uniform.
I filled two identical 1-tons tanks tanks to the same level and fermented them identically. Nothing was added to either tank, including no laboratory yeast.
One tank was 100% de-stemmed and the other was filled with 100% whole cluster.
The finished alcohols can be seen below. The first highlight is a de-stemmed tank. The second highlight it a 100% whole cluster tank.
I always knew the whole cluster made lower alcohol wines. That said, I never know it made for a reduction of nearly 1 degree!
Charlie, my opinion as to why the alcohol is lower in the whole cluster ferment vs de-stemmed is likely due to the temperature of the fermentation.
While we limit the temp of the ferment (through the use of glycol) so as not to allow the tank to warm above 84 degrees, the cap still is inevitably warmer in the de-stemmed tank as berries are on top of berries vs. stems intersecting throughout the tank which keeps things cooler. The stems act like a buffer. Like an egg carton crate. Separating the eggs from one another vs the de-stemmed tank which has eggs touching eggs throughout.
While I am aware that stems are made up of wood and water, it is no longer my opinion that the stem are leaching out water into the fermentation. I have read that others have had this belief and at one time I thought it possible, but no longer.
Greg, yes. Same starting brix, same native yeast strain.
Yes, I would bet the ranch on it that the choice of grape varieties doesn’t make any difference Stephen.
Here is a study stating that native or spontaneous fermentation is important factor on page 5 of 18:
The type of yeast and temperature of fermentation did not significantly affect ethanol production,pH or total acidity (p>0.05; Table 1). Ethanol content ranged from 10.8% to 12.2%v/v. However, in the case of spontaneous fermentation, ethanol content was lower in the wine fermented at 12◦C (10.8%v/v) than at 20◦C (11.8%v/v).
If I’m reading the report correctly, the residual sugars are also slightly lower in the batch with stems (1.7 g/L vs 1.7), but the malic acid is more than twice as high.
Since the RS is pretty similar, or a bit lower, are you saying that the alcoholic conversion ratio is different in the batch with stems, which fermented at a lower temp?
Interesting William. Thanks for sharing. When I was considering this post, I thought about Burgundy and contemplated that with warmer climate and higher alcohols, cooler ferments and the use of whole cluster might counteract their challenges due to global warming.
So the de-stemmed tank made 6.7% more alcohol that the whole-cluster tank. How much do the stems weigh? They are not contributing sugar, so the whole-cluster tank has less sugar (to be fermented into EtOH) from the outset.
The malic acid is significantly higher in the whole cluster tank. Do you expect to see a significant difference in total acid in the finished wine? Did the two tanks taste significantly different to you after primary fermentation?
Correct John, the alcohol conversion is or was much lower in the whole cluster lot.
Starting brix was 23.8 brix on each tank so the conversion was .519 for the whole cluster while it was .554 for the de-stemmed.
As you stated, additional gluc/fruc will lead to an increase of alcohol. That said, these are nearly identical and will make no difference in the final alcohol once all the gluc/fruc is assimilated.
The malic will not have an effect on the alcohol either.
We de-stemmed due to the small fear of smoke taint and due to this picture below I took. While the fires began on Tuesday and we picked on Friday night, I felt the there was still a few percent risk of smoke. Obviously if there are stems in the tank, that or they can lead to more taint if any is present. You don’t want anything from leaves to stems, etc in a tank if there is potential smoke taint as it will add more.
We de-stemmed everything except for 1 tank to hedge. There wasn’t enough time to pull samples and sent into the lab to analyze. There also wasn’t enough time to ferment a small micro lot in a bucket for sensory. All this said I am super happy to state that McDougall is 100% clean and will likely be the only red wine will release in 2020. As it looks right now, we are down 80% in production. We didn’t pick Falstaff which was a big hit for us.
Your final question is a good one and one I haven’t gotten through yet in my own mind. I am not sure knowing this will make much or any difference to my choices in the cellar. On a person note, I am not fond of de-stemmed wine from California as I find them to be more simplistic than the complexity which is obtained from using whole cluster. I also want my wines to age for a very long time and the stems without question allow for that by preserving the fruit. Now anyone can argue my opinion here, but I didn’t post to debate. I am simply sharing my opinion. I hope that helps answer.
