The taste of too much Kmeta?

Elmer said:

The wine had a rubbery taste to it.
Could this be too much kmeta?
Or the fact that I had not properly aired the one out for taking a sip?

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Secondary noob question, since my Tuscan was one month shy of my K meta-racking schedule, what I have been safe if I just had bottled it without an extra dose of K meta?

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sour_grapes said:

I am just a newbie, as a veteran poster has forcefully reminded me, so consider the source. Describe "rubbery" a little more. It did not smell like a bandaid, did it? (My understanding is that could be Brett.)



Or did it smell/taste like a rubber stopper, or something else?







I think this will be an unknowable question without testing. Better safe than sorry.

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Turock said:

Elmer--Excessive amounts of meta don't present wiith a rubbery taste. A rubbery flavor should always make you suspect an undetected H2S problem that is now exhibiting oxidized mercaptans. Not all H2S problems are detected thru smell, so you may think it's impossible to have H2S because you didn't notice any aroma.

To confirm this, I want you to run a bench test----take a small sample of the wine and swirl it with a penny. If the taste improves, then you know it is mercaptans. At that point, you would get some Redulees and treat the wine. Don't try to treat the wine with pennies as this can put too much copper into the wine. The penny is used ONLY as a test. If it does not improve, then you have to suspect other flaws like disulphides.

Of course, since this is only 1 gallon, you could also choose to toss it. Paying more attention to good nutrient management will prevent H2S issues in the future.

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Turock said:

Well--THAT was very interesting research from UC Davis.

It's not the degredation of sulfite. What it's discussing is the sulphide-based amino acids that produce H2S. In the absence of enough oxygen-based amono acids, some yeast will go after the sulfur-based ones. And as that article states, lack of nutrient AND vitamins together can play a huge role in H2S production. Choosing yeast strain is also noted, as some strains are more prone to H2S than others.

Bottom line is that I think the fault in your wine is sulfide based, due to an undected H2S issue. Try the penny test and see what happens.

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sour_grapes said:

Just to clarify: While I agree with the actions John suggests, I don't think this is the actual mechanism for H2S production during the active fermentation.

First of all, yeast autolysis is real, but the key word fragment there is auto-. The way it works is that, for whatever reason, a yeast cell dies. Then the enzymes in the now-dead cell begin to break down that cell. It is not the case that starved, zombie yeast cells start eating the brains of other yeast cells. However, John is correct: if yeast autolysis (especially of a large amount of sediment) is allowed to proceed for a long time, then sulfur compounds may be liberated. But this is different from the H2S produced during an active fermentation.

From my reading of the primary and secondary literature, this is my understanding of H2S production and its relation to N deficiency. Proteins are made of amino acids, and two important amino acids contain sulfur. The yeast has to provide the sulfur to form these compounds to the proper organelle during protein synthesis. It does so in the form of H2S, which it extracts from more complex sulfur-containing compounds. One organelle passes the H2S off to the organelle responsible for protein synthesis.

However, nitrogen is a major component of amino acids (hence the root amine, from ammonia.) If there is a dearth of N, the organelle responsible for synthesizing the sulfur-containing amino acid cannot do its job; this results in a surfeit of H2S, which the yeast then excretes.

As John points out, we are extraordinarily sensitive to H2S and thiols (larger SH-containing molecules). That is why they add a tiny (ppm) amount of methane thiol to your natural gas supply, so that you can smell when you have a gas leak. This is good for gas-leak detection, but the unfortunate result for winemaking is that we cannot tolerate very much H2S excretion by our pet yeasts.

Hope this helps!

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Turock said:

Elmer---The sulphide is due to the H2S--not sulfite in the meta. Don't be confused by the two. Meta is in no way resonsible for this fault.

Nitrogen is used by the yeast for amino acid generation. Lacking that, SOME yeast grab onto the sulfphur-based ones and generate H2S as a by-product. And,yes of course, the yeast is resonsible for the H2S production.

I believe that your issue is a case of undetected H2S. Did you use nutrient in this batch of wine and if so, how did you use it?

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Elmer said:

After it breathed for a bit the wine opens up, lost the rubbery smell, and had a taste of a well oaked super tuscan.

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Thanks for all the help!

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Turock said:

Nitrogen is used by the yeast for amino acid generation. Lacking that, SOME yeast grab onto the sulfphur-based ones and generate H2S as a by-product. And,yes of course, the yeast is resonsible for the H2S production.

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Turock said:

Well--THAT was very interesting research from UC Davis.

It's not the degredation of sulfite. What it's discussing is the sulphide-based amino acids that produce H2S.

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Hydrogen sulfide can come from different sources (Figure I). If sulfur is used in the vineyard too close to harvest, the reductive conditions that are created during fermentation can chemically convert this sulfur to hydrogen sulfide. Volatile sulfur compounds can also be formed during degradation of the sulfur containing amino acids, methionine, and cysteine, which usually are in low concentration in most juices barring supplementation.

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The majority of H2S produced occurs during the process by which Saccharomyces makes sulfur-containing amino acids.

Saccharomyces cerevisiae is able to reduce sulfate from its environment to sulfide and then incorporate it into amino acids through several more enzymatic steps (Figure II). Sulfide that is not incorporated into these amino acids is converted to H2S in a pH-driven reaction.

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sour_grapes said:

There is a lot of room for confusion, as amino acids are BOTH a feedstock for nitrogen (as Turock alludes to above) AND a principal product/component of growing yeast as they reproduce. However, there just isn't that much naturally occuring sulfur-containing amino acids in grape juice to serve as a feedstock to begin with; the source of S is actually the inorganic compounds sulfite and sulfate. (This has been established with radioisotopic labeling.)

Even this description is vastly oversimplified compared to the primary literature. The net implication is the same, of course, viz., provide proper nutrients to your yeast at the proper time. As Turock says, the nutrients are needed during the exponential growth phase, and not afterwards.

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In wine fermentations, H2S is largely formed by reduction of exogenous sulfate during the biosynthesis of the sulfur-containing amino acids cysteine and methionine [7, 10, 24].

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