Yet another H2S thread

[SLM]

My 2021 cab has been in carboys for a little over a year and is developing a slight sulfur smell. I used Avante yeast, didn't have any ferment issues, but now it's there. It doesn't taste off, just the smell. What would cause it at this stage? I know I should splash rack, sulfite, and I do have Reduless if necessary. I just don't know what would cause it and how to prevent it.

 

[CDrew]

Sulfur smell is not the same as H2S smell. If it's a sulfur smell that makes me wonder about your sulfite additions. Good luck solving this. I suspect that if a sulfur smell, Reduless will not solve it.

 

[Rice_Guy]

* are you familiar with the concept of ReDox? ,,, oxidation reduction potential.

sulfur chemistry is a reversible reaction driven by the redox potential (available oxygen/ oxidizer) in the wine:
2 H2S + O2. <=> 2 H2O + 2S

If you micro oxygenate as using a barrel/ HDPE carboy you change the redox potential and drive the reaction to the right
If you use Reduless which removes elemental sulfur you drive the reaction to the right
If you have a reduced environment/ squeaky clean air exposure, you drive the reaction to the left
If you add reducing agents as excessive potassium metabisulphite you drive the reaction to the left (do you test free SO2 ?)
Tannins act as oxygen sinks and I can’t predict if that is good or bad in your case, , , , , some of this is how sensitive a taster are you.

Renaissance yeast was a good start BUT a year out yeast are dead so you are living with redox chemistry, , , the smell threshold of methyl mercaptan is 2 ppb, mercaptans as well as hydrogen sulfide will mask young fruity aromatics, (I wonder if you have H2S ?) ,,, if the sulfur has reacted to a mercaptan it is harder to deal with, >>> ie reduce with ascorbic acid then pull the H2S out. Are you sure you are dealing with hydrogen sulphide/ sewer gas? which is detectable in the ppt level. , , , A test, does the smell go away if you shake a half filled sample jar? If you oxidize a mercaptan the threshold is 12 ppb. , , ,

My description of mercaptan taste in a white is bitter notes, loss of fresh fruity aromatics, , , , and I am curious what your cab tastes like, , , , since the local vinters club is dealing with/ trying to solve skunk in whites. Good luck PM me if you would like to talk flavors.

 

[winemaker81]

Rack the wine. if the "aroma" reeks, absolutely reeks (swamp gas, dog farts), it's H2S. If it smells like sulfur, it isn't. Excess K-meta smells like a burned match.

How much sediment do you have in the carboy?

 

[Khristyjeff]

@winemaker81 said, "How much sediment do you have in the carboy?"

I'll second that. I thought I had H2S problem but racking off sediment (I didn't think the lees were that thick), and adding K-Meta fixed the problem. At least it's an easy place to start.

 

[vinny]

* are you familiar with the concept of ReDox? ,,, oxidation reduction potential.

sulfur chemistry is a reversible reaction driven by the redox potential (available oxygen/ oxidizer) in the wine:
2 H2S + O2. <=> 2 H2O + 2S

If you micro oxygenate as using a barrel/ HDPE carboy you change the redox potential and drive the reaction to the right
If you use Reduless which removes elemental sulfur you drive the reaction to the right
If you have a reduced environment/ squeaky clean air exposure, you drive the reaction to the left
If you add reducing agents as excessive potassium metabisulphite you drive the reaction to the left (do you test free SO2 ?)
Tannins act as oxygen sinks and I can’t predict if that is good or bad in your case, , , , , some of this is how sensitive a taster are you.

Renaissance yeast was a good start BUT a year out yeast are dead so you are living with redox chemistry, , , the smell threshold of methyl mercaptan is 2 ppb, mercaptans as well as hydrogen sulfide will mask young fruity aromatics, (I wonder if you have H2S ?) ,,, if the sulfur has reacted to a mercaptan it is harder to deal with, >>> ie reduce with ascorbic acid then pull the H2S out. Are you sure you are dealing with hydrogen sulphide/ sewer gas? which is detectable in the ppt level. , , , A test, does the smell go away if you shake a half filled sample jar? If you oxidize a mercaptan the threshold is 12 ppb. , , ,

My description of mercaptan taste in a white is bitter notes, loss of fresh fruity aromatics, , , , and I am curious what your cab tastes like, , , , since the local vinters club is dealing with/ trying to solve skunk in whites. Good luck PM me if you would like to talk flavors.

Did you read or book, or something?

Or, all of the books EVER written on wine making?

 

[winemaker81]

Did you read or book, or something?

Or, all of the books EVER written on wine making?

It's entirely possible he wrote the book.

Do what I do -- open your favorite search engine in another tab, and go back to school.

Adding onto @Khristyjeff's comment, if caught early, stirring vigorously will drive off the H2S gas (which is noxious, run a fan!), and add a single or double dose of K-meta will render the remainder harmless. If that doesn't work, then use a product like Reduless.

If mercaptans form, the treatment is ascorbic acid. This is a strong acid, so use as little as possible. A few years ago I had 15 gallons with H2S, had to use Reduless (which worked!), but had mercaptans form. IRC, I calculated how much ascorbic I needed (used an online tool), and added 25% of the calculated amount. It took months, but it worked and the wine is fine.

 

[Rice_Guy]

Did you read or book, or something?

This link from U of Va is a good summary of sulfur chemistry ex. how to isolate the real issue or the use of ascorbic acid to remove mercaptans.
https://www.apps.fst.vt.edu/extension/enology/EN/134.htmlIn "WINE FAULTS" The AWRI has a procedure out for mercaptans which is essentially react with 10mg/L ascorbic > wait 24 hours > react with more ascorbic > wait again > finally pull the sulfur compounds out

By the way @SLM if there is an air lock on the carboy I would assume that there is enough oxygen transmission to be reasonably oxidative, ,,,, not as much as a barrel but enough.

no, but chem is a good tool for guessing what is happening inside of a stainless steel processing tank

 

[SLM]

Ask a question on WMT, get an education! I love it!

It's not sewer, it's burnt match
It's over a year old, had a few rackings, so very little sediment at this point
Of 6 carboys, only 3 stink, the 3 I have been messing with, tasting, tweaking with tannins, topping. The 3 that I've left alone smell fine
I racked them all and added SO2, 24 hours later the smell has diminished greatly but I still detect it slightly
I do not test for free SO2. I just add 1/4 tsp every 3 months. This batch is overdue at 3 1/2 months, so it doesn't seem excess SO2 is likely. The other 3 carboys are on the same schedule
All carboys have those silicone bungs with one way valves

 

[winemaker81]

@SLM, no H2S is great! If you have burnt match smell, AFAIK, that's excess SO2.

It should go away in time, as free SO2 is used up. Don't add more K-meta to those carboys.

My Tempranillo developed H2S, which I caught early, and overdosed with SO2, but it smells fine now.

 

[VinesnBines]

I

This link from U of Va is a good summary of sulfur chemistry ex. how to isolate the real issue or the use of ascorbic acid to remove mercaptans.
https://www.apps.fst.vt.edu/extension/enology/EN/134.htmlIn "WINE FAULTS" The AWRI has a procedure out for mercaptans which is essentially react with 10mg/L ascorbic > wait 24 hours > react with more ascorbic > wait again > finally pull the sulfur compounds out

By the way @SLM if there is an air lock on the carboy I would assume that there is enough oxygen transmission to be reasonably oxidative, ,,,, not as much as a barrel but enough.

no, but chem is a good tool for guessing what is happening inside of a stainless steel processing tank

U of Va is not VT. There is The University of Virginia in Charlottesville- Mr Jefferson’s University and there is Virginia Polytechnic Institute and University or now known as Virginia Tech at Blacksburg. VA Tech has an excellent viticulture and enology research center in Winchester and this will be the group that produced the linked article.

Sorry to be snarky but to confuse the two institutions causes great discord.

 

[Rice_Guy]

Opinion, folks do overkill, ,, we should rack/ add metabisulphite when there is a purpose for it, ,,, NOT based on the calendar. I try to rack and add meta three times before I bottle. Reading articles that make more sulfury wine when adding SO2 to the must makes me question that one too.

i do not test for free SO2. I just add 1/4 tsp every 3 months. This batch is overdue at 3 1/2 months, so it doesn't seem excess SO2 is likely. The other 3 carboys are on the same schedule
All carboys have those silicone bungs with one way valves

In the old days great grandpa would make wine without adding metabisulphite. Humm, ,, You are making a red which has tannins which act as antioxidants much the same as great grandpa. We all have variation in repetitive process, if I do it without paying attention I say my process is sloppy Ex how much splashing going into a carboy or low temp which makes oxygen more soluble or using a volume measure which can deliver different weights of active chemical or more lees (antioxidant) in one carboy vs another. ,,,
There is positive info in variation, ,,, in the pilot plant we would do repetitive batches and test every finished product to decide where to set the processing controls on the big lines.

 

[sour_grapes]

Sorry to be snarky but to confuse the two institutions causes great discord.

I agree, but try having Penn as an alma mater!