Expansion during fermentation?

How often do winemakers have to drain or pump off wine from a fermentation tank because of expansion?

Is this expansion unpredictable? Cuz I’m wondering why you wouldn’t just make sure the tank is large enough to allow for expansion.


Expansion is completely predictable, and one of the main reasons we have to drain off to keep the tanks or bins from overflowing is that on the day of harvest, we were out of fermentation space, and had to fill things up more than we wanted to. There are other reasons, but that’s the most common excuse in my winery.

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okay, the lack of fermentation space makes sense. In a perfect world, you’d have another tank.

Yes, I’m envious of the wineries that have enough fermentation and floor space so they don’t have to turn over fermenters in a given vintage. Sometimes even those wineries run out of fermentation space in an unusually large harvest. A winemaker, cellar master, etc., might be overruled by an owner or higher up who decides this winery needs to make more of a certain wine, so they give a last minute go ahead to additional tonnage for which they don’t have fermentation space or even barrels. Or, a winemaker has an excellent relationship with a grower, and wants to keep it that way, so they agree to take extra fruit, beyond what the winery is prepared to handle. Many things can come up during harvest. Winemaking is 85% about the fruit, 5% about the winemaker, and 10% is left for logistics, my 5 cent breakdown.

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Often for me when fruit arrives I am more worried about getting it sorted and into the winery. Its easier to fix things on a not fruit sorting day for me. This year for example a certain block picked out at 1.8 tons. I usually like the crew to send me .4 ton (900lbs) bins so that I can fit 2 into each t-bin fermentor and have .8 ton in them so that they don’t souffle. So rather than fill another bin with very little fruit I kept the fermentors over full with not enough room for expansion. Once things got warm and kicked off I bucked out enough into food grade 45 gal containers to allow for expansion then post peak I added the fruit back into the bin. The expansion volume was out of the main fermentor for 5-6 of the 32 days that batch spent on the skins. Small ferments have a tough time getting warm enough for my liking so I don’t do anything in macro picking bins and stick to double walled t-bins hoping for peak temps in the mid 90’s for at least 24 hours.

Warmer ferments will usually expand a little more as the cap gets pushed up higher due to more rapid co2 production and thus cooler ferments will expand less. Lots of folks overfill and pull saignee juice after a night so they will over fill then pull 10-20% of the liquid out to increase skin to juice ratios.

One thing I never wanted to have to do was press off to early or let fruit hang to long to make room in the cellar. I have not had great results with doing those things in the past. It happens all the time Its definitely different if you making a wine gambit of varietals from a wide range of climate but I have 100% tank space for a given years harvest. I do not flip or reuse my fermentors in a vintage. Part of that is I only work with one appellation, one vineyard, and one varietal. I also like 21-28+ days on the skins. I don’t use temperature control and press at cap fall which is extended due to my use of whole clusters.

With that high fermentation temp, are you looking for some fruity ester production along with increased extraction?

I ferment in 32gal containers and “only” reach about 85F at peak, though I also use on Lallzyme EX to help with extraction. Too late for this year, but your comment makes me wonder what I’m missing. Maybe I should A/B test two primaries next year, one with heater assistance and one not.

There are several reasons I like a warmer peak for 24 hours. When I was making personal wine in small 32-45 gallon containers we used blankets to try to get them warmer. I tried fish tank heaters once with meh results. I found the best was to keep them full and just like a t-bin that is double walled we would use 2 containers, one nested inside the other just like how you would stack them and that seemed to work best.

Warmer peak temps help with setting color. I don’t use inoculated yeasts (like RC212), cold soaks (temperature control), tannin additives, or enzymes for additional color in the final wine. I get plenty of extractions from 3-4 weeks on the skins pressing at cap fall. I use a food grade mesh covers to keep fruit flies and the like out of the ferment yet allow it to breathe easily in both directions o2 in and ETOH/volatiles out. At the peak temps I get with open top fermentors alcohol and other volatile compounds (i.e. any EA from the early stages) blows off the ferment. I get conversion rates of .55-.57 (lower end of rates if using glu/fru higher if using brix) with my PN’s mainly due the mid 90’s peak and lack of soak ups. I consider any soak up to be a pick I waited to long on so I don’t get them and am not of fan of ferments that soak up. I see the same or even a little lower after a couple days due to whole cluster usage. I am able to pick with an average approaching 24*(Dijon clones a little less usually and Pommard blocks a little more usually) and still get final blends in the mid 13’s most years.

I’m very new to this forum AND winemaking, and not sure anyone is still following this thread, but if you are…My most recent fermentation got overheated, mid-90’s and led to an H2S problem that lasted after racking off the gross lees. At a loss for how to remedy the situation, I used an old trick someone mentioned and filtered the wine through PVC stuffed with a 100% copper pad. That worked, though at the expense of some aroma.

The real question, though, is how at such high temps do you prevent the formation of sulfur? I used D254 which is supposed to be a low producer of H2S. While my YAN didn’t warrant the addition of nutrients so early, and likely facilitated the hotter ferm temp, is there a difference in H2S formed from that mistake vs. just running a hot fermentation? Thanks for looking!

There are a lot of reasons H2S can form. Just a warm/hot peak temp should not do it. IMO its usually not enough oxygen in the ferment. When its peaking 3 or more punchdowns with lots of splashing is our protocoll.

Was you starting brix over 24*? The lower the better IMO for this issue.
Have you used that yeast before (I know next to nothing about commercial yeasts)? If I ever inoculated I would use 5-10 or more strains to make sure they can handle all varying brix/temp/etoh variations.
Did you add so2 before fermentation? if so how much? Too much can cause the yeast to struggle.
Was there any bird damage, mold, sunburn? All things that can lead to excess VA/EA and otherwise stress yeast
Open or closed top fermentor? Closed tops usually increase final ETOH and can be harder to get enough O2 into the ferment.

Copper sulfate is the best way to make it go away, but I have never used it so not sure how much or how well it works.
Open top or closed top?

You can get HS2 quite easily with low nutrients. Ferments in closed spaces can be susceptible, so often the barrel fermented whites can be a common problem area. I’ve never had HS2 problems because of fast or hight temps. HS2 tends to go away with time and with splashing you can help it along.

Hi and thanks for the quick replies. Fruit was sourced from Suisun Valley, and the merlot came in at 25.5 brix, TA was 0.51 g/L, pH at 3.35 and YAN at 372 mg/L. I did S02 prior to adding pectinase then did a 4 day cold soak at 50° +/- F. The YAN was fine, and I believe the source of the over-heated ferm may lie in the premature/unnecessary addition of nutrients at 2-3 degree brix drop. Following a formula laid out by Scott Labs on when and how much to add (GoFerm Protect Evo at inoculation/Fermaid O at 2-3 brix drop/Fermaid K at 1/3 sugar depletion). The YAN was already off the charts, but at 2-3 brix drop I added the same amount of nutrient to the merlot as I did to the Cabernet which had YAN of 165 (just after punch down I had my DOH! moment, when I realized I shouldn’t have done anything to the merlot, but it was too late).

Overnight the temperature in the merlot went off the charts so I tried to cool it down through punch downs and frozen water bottles. Fermented in small 32gal food grade plastic Brutes with a sheet covering so it could breath and always did two vigorous punch downs each day. The CS had the most sunburn, while the merlot looked pretty good, though I tried to separate the sunburned/raisined fruit as best as possible. Don’t think there was any bird damage. In the end, I followed the advice of a winemaker from a group out of club in Canada (chemist by trade) who suggested running the wine over a clean, sanitized 100% copper scrub pad stuffed into a 1" PVC pipe. His indication was that at this early stage, it was still H2S and mono mercaptans, so intervention with ascorbic acid and copper sulfate wasn’t necessary. Seemed to work, but lost some aroma.

In the end I’ll need to pay closer attention to the nutrient schedule. I’ll need to use commercial yeast until I’m certain that the natural yeast can accomplish the task.

Sounds like the ferment just got going too fast from excess nutrition. In practice, heat and pace mostly go together and are mutually reinforcing. It’s the pace of alcohol production that the yeast have difficulty excreting fast enough to prevent toxicity within the cell that’s the real stressor. Often the yeast dies of alcohol toxicity, but I’m guessing the stress involved caused the H2S production. In this case, you might have slowed things enough to save the day when you cooled it down.
You probably got good advice in betting on it being H2S early on, but it’s still better to actually know what form of sulfide you have. What’s good for one form is bad for another – a treatment that appears to work immediately can just kick the problem down the road. There are cheap kits out there (I think Gusmer and maybe Napa Fermentation) that enable you to diferentiate between forms of sulfides.
I agree with the prior advice to use copper sulfate (at a controlled dosage that you figure out with bench trials) rather than an unknown dosage with the copper pad. Copper, in combination with iron, promotes oxidation, and you’d like to go as light as you can. I run into reduction with rose, which I’m not anxious to aerate. If I have to use copper sulfate, I follow with PVI/PVP afterward to scrub any copper from the wine.

The textbook reason for H2S production is yeast stress due to inadequate nitrogen nutrition. Some varietals are more prone to this, as our Syrah vineyard is.

We had a big problem with this one year, even though I stay on top of the Fermaid additions. If not blown off in a hurry H2S goes on to form disulfides and mercaptans that smell worse and are much harder to treat. We were successful with ascorbic acid followed by CuSO4, but if you read up on it most of the copper and sulfur stays in the wine as a colloid. (Lab test showed Cu levels lower than permitted in drinking water)

Prevention is best and I’m a big fan of Renaissance Yeast, which does not produce H2S and has produced strong clean fermentations since we started using it in 2017