Hello yes, and welcome back to another edition of the slightly drunk in the garage reflective blog. Today our journey began with an espresso martini, lovingly crafted from Polish vodka, Kahlua and an espresso brewed from a fine blend of home ground coffee beans from countdown. This was quietly followed up with a tasty nip of Czech rum and is currently being chased by a tasty nip of Czech rum. Now that the formalities are aside I should begin todays enthralling discussion on sulphides. Here we go.
I’ve had many a couch connoisseur pause their playstation, pull the lint from their belly button and turn down the fine glass of wine they have just been offered and exclaim, “I don’t drink wine because the sulphides give me bad hangovers”.
In fact you are more likely to have an asthma attack from sulphides or sulphites in your wine then get a headache or hangover. Now that I’ve got that rant out the way, what are sulphides, how are they different to sulphites, and how do they occur in a wine? Let’s keep things simple, especially as I’m not good at pretending to be smart. In wine, sulphide compounds are naturally formed during the fermentation process or as a wine ages. In high enough concentrations they can be perceived as a fault and some are referred to as volatile sulphur compounds (VSCs), or volatile thiols. Sulphites are much the same but have a slightly different molecular makeup. Besides one sulfur atom, sulfites have three oxygen atoms. This addition causes the creation of bonds in the ion, another feature sulfide ions do not have. However, sulfite and sulfide are similar in ways. Sulfite ions, like sulfide, have a negative two charge. Sulfite ions have this formula: SO2−3 where as a sulphide will have this: S2− . Sulfite ions are regularly used as a preservative in wines.
H2S (hydrogen sulphide), is the first sign that you may have some potential issues with VSC and is often noted in young wines, generally caused by the reaction of the yeast to the elemental sulphur in the environment of the grape juice. Hydrogen sulphide will become detectable at around 10 ppb and will give off the aroma of rotten eggs or a bachelors bathroom after a long night on the turps. It is also referred to as reduction and is best treated as soon as it is detected by aeration or the addition of copper sulphate, or if noted during high ferment the addition of nitrogen based yeast nutrient such as DAP, (diammonium phosphate) can be beneficial. By leaving H2S in the product for too long will cause it to react with the alcohol being produced by the fermentation, creating your level 2 boss called Ethyl Mercaptan.
No a mercaptan in not a leader of the mer people, but the beginning of a headache. Not the alcohol induced kind, we’ve been over this. But the arrival of detectable VSCs or volatile thiols. Remember many of these compounds are naturally present in a wine and offer no issue at low concentrations. In some varieties they can even impart positive characteristics, but poor wine making practices or storage conditions will cause the concentration of these thiols to breach the sensory threshold, (which can be very low), and give off the sweet aroma of fecal matter or if you’re lucky they will only smell like rotten vegetation or burnt rubber. Fun fact, often Ethyl Mercaptan is added to natural gas to help detect or warn of gas leaks. Treatment of mercaptans in wine are much harder than that of H2S and options are limited. Copper sulphate is again often employed to treat these mercaptans by binding them and causing them to precipitate out of the wine. This however can be problematic as some markets limit or even prohibit copper additions in wine so you gotta be bang on with your additions to avoid or limit any residual copper and, unlike H2S, mercaptans can only be reduced and not eliminated. Again, if left untreated these mercaptans can oxidize and stabilize in your wine to create your level 3 boss. Dimethyl sulfide (DMS).
Treatment for dimethyl sulfide can also cause other negative effects on your product and may not always be successful. DMS at lower concentrations, like thiols, can have a positive sensory impact on your wine and will often present itself more commonly as a wine ages. Higher concentrations of DMS will present itself as a cooked cabbage, burnt rubber or garlic aroma. While they may be less pungent than mercaptans, its still not great for the consumer to think of corn fritters when chucking back a glass of liquid courage before their first tinder date of the season. A common way to treat a DMS fault in a wine involves adding ascorbic acid and SO2 to try and reduce these compounds back into mercaptans and then treating these mercaptans with copper as mentioned above. It may also be possible to reduce the aroma by reverse osmosis or nitrogen sparging. However, as the DMS doesnt usually present itself until a wine is finished and aged, it may be too late as the product maybe already be in a bottle. If in storage, any additions and/or other processing of the product will be sure to have affects that can be detrimental to the quality of the finished product.
The use of a Cu/Cd diagnostic test maybe helpful in identifying early stages of detectable sulphide compounds in your wine, allowing you to formulate a plan to treat your product for the appropriate sulphide related fault before it becomes a real issue. Remember that while copper can be an option to treat a wine, cadium salts are a not an option. This test is purely for diagnostic purposes only.
In conclusion, it seems the best way to avoid some swear words directed at an innocent batch of wine is to remain vigilant and diligent throughout the winemaking process when it come to identifying and dealing with the progression of sulphides, especially in the early stages. Be proactive and decisive before it becomes like the rust in your car. Cheers.
Published by Adrian Green.