Egg smells and how to deal with them

[SiSandrine]

Following on from Tattys thread.
I had some white grapes from local garden which I turned into wine early this autumn. All went well through primary but I left it on the gross lees too long (probably only a few days) and it went eggy.
I seem to have salvaged it by splash racking a couple of times, adding in a small tin of Youngs white grape concentrate, a little additional sugar and a strong yeast starter with added yeast nutrient at the appropriate level. My theory being that a strong referment would blow off further any odours. OK the wine is a little higher in alcohol but it seems to have worked (3 weeks after the smell is gone). One beneficial side effect is that there is a very slight yeasty/bready taste resulting not unlike a sur lies wine e.g. muscadet sur lie. It is a good flavour but too acidic at the moment - that is the next challenge. Thanks for the copper tube advice - i'll try that if this happens again.

On bottling: I did read that if you use chlorine based products for sterilising bottles or corks (e.g. Milton/VWP/bleach) that smells can develop post bottling as solution can become trapped and react with the bacteria already present in the corks, likewise if too much strong sulfite was left in the bottle/cork when the wine went in that may have reacted in some way, particularly if the wine was at the high end of the hydrogen sulfide range (but still pre-sensory) already. Not experienced that myself though so it is only a theory - has anyone else?
My wife has given me pre-warning that she isn't going to drink the "egg-stuff". Better hope she can't remember when I offer it then!

[NorthernWiner]

Just a couple of clarifications...

First, chlorine doesn't promote hydrogen sulphide (aka H2S, or "rotten egg"), but rather a different type of spoilage known as "cork taint" (aka 2,4,6-trichloroanisole, or simply TCA). I don't believe you were implying they were the same, but I want to emphasize there is a difference.

With regard to H2S, there are a couple of ways to deal with it. And whenever possible, it should be dealt with straight away rather than waiting. As it sits in the wine, it interacts with other compounds, making it more difficult to be rid of over time.

First, it's helpful to understand what causes it.

During active fermentation, if yeast don't have access to proper nutrients, they will become "stressed" and begin releasing the compound. While it's easy to assume that yeast can live on sugar alone, it actually makes them quite cranky. Just like you and I, they require a balanced diet, including nitrogen (yeast are plants after all), amino acids, and vitamins (particularly B-complex). To put it in another way: if you were to live on only sugar, you would likely also be irritable and emit foul odors.

The second cause of H2S usually comes post fermentation, as the dead, flocculated yeast begin to autolyze, or decay. Yes, they begin to rot and stink. This can usually be avoided by either racking off the dead lees, or by simply stirring them back into solution periodically, which allows the sulphur compounds to be driven off. Lees don't become a problem unless there is a thick layer, and it begins to compact in the bottom of the carboy or DJ.

If caught in the very earliest stages, for example, in the early phase of active fermentation, you can sometimes do nothing more than give the wine a brisk stir to incorporate some oxygen and drive off the offending compounds. If there is still more than half the sugar remaining, you can also add a complete yeast nutrient at this time. Doing these two things will alleviate the problem about 90% of the time.

In latter stages, H2S begins to bind with other chemical compounds to form mercaptan. Mercaptan is a little more difficult to remove. The best weapon to fight it is copper. Copper binds with both sulfide and mercaptan, and forms yet another, less offensive, compound that simply sinks to the bottom of the vessel. One method for introducing copper is by stirring with a copper pipe, or running the wine through a funnel into which a copper kitchen scrub pad has been wedged.

Another method is to add a very dilute copper sulphate solution to the wine. It's more precise, but is also more difficult to use and has the added problem of being highly toxic. You literally only want to add a few drops to the wine. In the US, we refer to this copper sulphate solution "the blue bomb," owing to the neon blue color. Again, I want to emphasize the toxicity. Don't use it unless you know precisely what you are doing, or, worst case, you could potentially end up with kidney damage.

Yet another method for removing H2S post fermentation is by adding a yeast hull product to the wine. In large enough quantities, yeast "ghosts," as they are sometimes called, will absorb sulphur compounds as they sink to the bottom of the holding vessel. This method does not work in all cases, however, and often requires supplementing with copper (liquid or metal) to complete the cleansing process.

I hope this helps a little. Hydrogen sulphide production is a complex topic. There is a very good article to be found at the following Candian winemakers web site, that goes into quite a bit more detail:

http://www.bcawa.ca/winemaking/h2s.htm