Fermentation funk odors

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verdot

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Hi everyone. I’m fermenting my first crop of merlot and cab sauv from my small vineyard, and have a about 12 gallons of must fermenting at proper temps for the past few days. Everything seems fine, but I’m getting a strange, funky, rotten grape and deviled eggs (not sulfur) kind of odor that’s very unpleasant. Should this be cause for concern?
 

verdot

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I did add yeast nutrient when the yeast were pitched and a few days after fermentation began.
 

CDrew

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It sure sounds like H2S. And yes, address immediately. Is it done fermenting? if not, some more nutrient would be my next move. What yeast? Next year consider an H2S preventing yeast like Avante. Read up on these Renaissance yeasts which cannot produce H2S.

If its done fermenting, you might try to splash rack. When that doesn't work, consider Reduless. Full disclaimer-I've never used, but have heard it's very effective.
 

Juniper Hill

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Agree with nutrient if still fermenting. Also, lots (3 or more per day) of punch downs will introduce more oxygen and help drive off sulfur. Delastage is another way to add more oxygen, but is a bit of a pita.
 

Cap Puncher

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As CDrew mentioned, reduless is a good option. I have used it and it works for smaller issues. For now, I’d add nutrient/optired or nobelese if you have it. Delestage is a good idea with nutrient. It really depends what part of fermentation you are in. Lots of oxygen is good, but actually can cause the yeast to want more nutrients. Scott Labs has a sulfur like odor protocol for red wine that you should look at. I wouldn’t add reduless until after alcoholic fermentation is complete.
 

verdot

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Thanks for all the great suggestions, guys. I used red star premier rouge yeast, and the must is getting three punch downs a day. I’m going to hope for the smell to dissipate more after pressing today. I was mainly curious if a musty/unpleasant smell was expected a few days into fermentation with grape must or if it should be expected to smell more like the kits I have used in the past which were more of an expected yeast/fruity fermentation smell. Does seem like H2S or some other byproduct may be lurking, though, but I’ll resist intervening with additives at this point other than some nutrient at pressing and let it run its course.
 

balatonwine

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deviled eggs
As other said, this is most likely hydrogen sulfide (H2S).

And yes, needs to be dealt with quickly.

But it can be complicated. To deal with all the possible causes, and different solutions, I recommend reading the link below, from UC Davis. Because H2S can form for many reasons, depending on many factors, some of which have nothing to do with needing to add more yeast nutrient.


Ergo, it is complicated.

My personal suggestion, is to really first check if you might have an overly reductive environment. That is, not simply should you punch down the cap 3 or more times a day, but give it a good splashing stir each time for a minute or two. If you notice a decline in odor in 24 hours, and complete removal within 48 hours, then your wine was simply over reductive. Keep up this aeration schedule till about 2/3 of the sugar is gone. Then reduce severity to not over oxidize the wine (but keep a daily smell test and repeat the rigorous procedure if needed).

If the 48 hour test above fails, then, and only then, would I recommend trying to correct via chemistry with more nutrients. But adding nutrients if not needed now, might cause issues later.

If you have H2S later in fermentation, then other actions should be considered. See the above article for ideas.

Hope this helps.
 
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winemaker81

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And yes, needs to be dealt with quickly.
This is essential advice. Most things in winemaking are "wait -n- see". H2S is the counter example. The longer you delay, the more difficult it will be to correct it. H2S forms mercaptans, and once that happens you have to treat that off-flavor as well.

Immediately stir very well and double-dose the K-meta. Ensure the area is well ventilated.

Reduless works well, but hopefully the stirring/K-meta will fix it so you don't need it. It bleaches the wine and mutes flavors. This is better than throwing the wine out, but it's best to avoid it if you can.
 

Ct Winemaker

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There are a variety of smells associated with fermentation most of which are normal and not necessarily “good”. When the fermentation is fully developed (cranking along at high speed!), there is usually associated heat and some funky odors. What you are smelling may be completely normal and not an issue. As long as you have been using an appropriate nutrient protocol ( fermaid O and K for example), temps aren’t out of control, and your punching down regularly (3 time per day), I would go easy with attempting to adjust too early. Also, not sure about the k-meta suggestion. If that is referring to potassium Metabisulfite, adding it during fermentation could end in a stalled fermentation. It should be added only when fermentation is complete (including Malolactic Fermentation if you are doing that).
 

winemaker81

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Also, not sure about the k-meta suggestion. If that is referring to potassium Metabisulfite, adding it during fermentation could end in a stalled fermentation.
H2S is an unmistakable odor. Rotten egg and swamp gas are good descriptions. When this occurs, there is nothing worse that can happen to the wine. Untreated, the wine is destroyed, so fermentation stopping is not honestly a concern. Do a search -- vigorous stirring and a high dose to K-meta (potassium metabisulfite) is a recognized first treatment. If fermentation is not completed, adding nutrient is suggested.
 

Cap Puncher

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Reduless works well, but hopefully the stirring/K-meta will fix it so you don't need it. It bleaches the wine and mutes flavors. This is better than throwing the wine out, but it's best to avoid it if you can.
Again, I agree that reduless works well, but to say that it “bleaches” wine and mutes flavors is only true if you give large/ multiple doses.

If used in proper dosage, it works great. I have had wines with the aroma slightly muted by reductive sulfurs but not enough to really detect. Add a small dose of reduless and it unmasks the true fruit aromas and end up being wonderful.

Dose and bench trials are key (just like with most things in wine)

I don’t disagree with the Kmeta with a good stir/splash rack but I would wait until alcoholic fermentation is complete.

Here is the Scott labs protocol for sulfur aromas in reds:

 

winemaker81

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Again, I agree that reduless works well, but to say that it “bleaches” wine and mutes flavors is only true if you give large/ multiple doses.
I used the minimum recommended dosage and it affected the color. I had another carboy of the same wine to compare against.

Of course, the best way to deal with H2S is to use sufficient nutrient before and during fermentation to avoid it completely!
 

verdot

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Thanks for the replies. Definitely seems like low oxygen and nutrition at start of fermentation is an issue. I ordered some go-ferm protect evolution for next year and will be more precise with nutrient addition next time around and be more selective with my my grapes. Some bad and broken ones may have made their way into the must. Will be splash racking a bit as you suggested Mario and will just hope it dissipates with time.
 

Juniper Hill

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I've had good luck with reduless for H2S that didn't clear with other measures. I haven't noticed any muted flavours, but of course compared with rotten eggs just about anything else is gonna be good.
 

Cynewulf

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Had the same problem last year with a Pinot Noir. Solved the problem by splash racking several times. Got lucky.
Same here. I had the issue with a Grenache bucket I was fermenting with some pressed pomace last year. I splash racked once or twice and the H2S smell dissipated over the next month or two and was completely gone when I bottled this year. I didn’t add anything, not even SO2. YMMV, just another reference point.
 

Mario Dinis

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Same here. I had the issue with a Grenache bucket I was fermenting with some pressed pomace last year. I splash racked once or twice twice and the H2S smell dissipated over the next month or two and was completely gone when I bottled this year. I didn’t add anything, not even SO2. YMMV, just another reference point.
I also didn't add anything.
 

winemaker81

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Treating H2S depends on how early it's caught. If detected before mercaptains start forming, stirring may be enough. In my situation a year ago, that was not the case, so I had to do a more extensive treatment, and months later treated with ascorbic acid to handle the mercaptains.

The moral of the story? Use sufficient nutrient and sniff test the wine daily. I admit that my encounter has made me paranoid. But better paranoid that a carboy of bad wine! 😉

Note on ascorbic acid -- I use a very light dose as it can made the wine very sharp. It took nearly 2 months for the ascorbic acid to work. Once the H2S is handled, the wine is back to "slow, steady, and patience" as the mantra.
 
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