Preventing Three Big Wine Stinks

Preventing Three Big Stinks 

You emerge from the cellar beaming, proudly cradling one of your prized bottles in the crook of your arm. You bring it to the table, pop the cork, splash out the first precious drops into the awaiting glasses of your dinner guests. And a sinister stink redolent of swamp water permeates the room as you quickly rush to open a window.

All right, maybe it’s a slight exaggeration. But it doesn’t take much to pollute what should be the aromatic and pleasant headspace in your wineglass. So what happened? You’re a conscientious winemaker, you tell yourself. The last bottle you opened from that batch tasted fine. Before you beat yourself up over a case of cork taint, realize that these inconvenient and smelly off-characters happen to the best winemakers. With good sanitization practices, attention to detail, and a little forethought, they can be prevented.

Acetic Acid (Vinegar)
A crisp green salad, a little glass of vino, some crusty French bread on the side — what could be better? Nothing, except for the fact that you want to make sure the vinegar’s on the salad and not in the wine. If you’ve ever taken a sniff of a wine and thought of last night’s mixed greens, chances are the wine was contaminated with acetic acid.

Acetic acid (what makes vinegar sour) comes into play in a wine’s aroma and taste when certain kinds of bacteria come in contact with wine and turn some of the alcohol into acetic acid. These bacteria naturally live on winery surfaces (floors, beams, equipment) and can be introduced to the wine through day-to-day contact or by other vectors such as insects (like those pesky fruit flies that like to hang around during harvest).

Don’t let their omnipresence put you off, however. Acetobacter (the official scientific name for these guys) can be controlled in a number of ways. To develop an anti-Acetobacter strategy for your
winemaking program, keep in mind three things: Acetobacter love unsanitary wineries and moldy grapes, need oxygen to grow, and absolutely hate sulfur dioxide.

So a plan to control these bacteria should be a comprehensive one that starts taking effect before the first load of grapes ever enters your home winery. Don’t accept any fruit that’s so badly damaged that it’s got oozy, moldy, unsavory growth all over it. Even partially rotten grapes are heaven to any self-respecting Acetobacterium. Aside from harboring large Acetobacter populations, grapes in less-than-acceptable shape can also be a primary cause of stuck fermentation, which can lead to high residual sugar levels, secondary fermentation after bottling, hydrogen sulfide production, and a host of other problems. Don’t want problems? Don’t use second-rate fruit.

If you’ve got perfectly sound grapes and want to make sound wine that is free of acetic acid, you’ve got to control the Acetobacter population by excluding the bacteria themselves, by cutting off their oxygen supply, or by killing them with sulfur dioxide. Reducing their numbers on equipment and in the winery can be kept in check by vigilant sanitization and by the use of screens and other devices to keep down the number of fruit flies and other insects. Bugs and their ilk have the nasty habit of carrying scores of Acetobacter on their little legs and wings. Have a few of them land in an uncovered vat of wine and bingo! Instant vinegar.

Even if the errant fruit fly or two do escape your watchful eye, however, you can still exclude the bacteria’s oxygen supply. The home winemaker can easily do this by minimizing headspace in carboys and barrels, by topping up all containers frequently, and by blanketing the wine in a carboy or barrel with a layer of inert gas such as nitrogen or carbon dioxide.

In addition to these methods, you should also use sulfur dioxide in sanitizing solutions and as a wine additive (30 milligrams per liter is a good guideline) to further discourage Acetobacter and other microorganisms that can ruin wine.

What should you do if your carboys start to smell like a vinegar factory? Well, there really isn’t one definite cure-all. If you’ve just started to notice the smell, it could be that the bacteria haven’t gotten a firm hold on your wine yet. This is a good thing, because you might be able to discourage any further growth by adding some more sulfur dioxide or by blanketing the wine with carbon dioxide gas. Unfortunately, if the acetic acid levels are very high, chances are these techniques won’t do you any good because the bacteria have already spoiled it.

Hydrogen Sulfide (Rotten Eggs)
Hydrogen sulfide has a smell that is certainly one of the most objectionable off-odors in wine-making. Fortunately, it’s also one of the easiest to avoid. Hydrogen sulfide (H2S) is caused by the yeast reacting negatively to elemental sulfur on the fruit surface, to stuck fermentation, and/or to poor yeast nutrition. As opposed to acetic acid, hydrogen sulfide is not caused by any kind of foreign microorganism contaminating the wine; it’s produced by the yeast itself. The key, then, to producing H2S-free wines is to provide your yeast with the kind of environment in which they will be healthiest.

If you’re buying fruit from a vineyard (or grow your own), make sure that it wasn’t sprayed with sulfur for at least a couple of weeks. Growers use sulfur to prevent mildew and fungus. The yeast will metabolize the sulfur powder and excrete it as hydrogen sulfide. While you’re at it, choose a strong, proven yeast strain (such as Prise de Mousse) that will be able to efficiently carry out the fermentation to completion. Avoid so-called natural fermentations. They are perfect breeding grounds for wild yeast, some of which can be rampant H2S producers. Always add a commercially accepted yeast nutrient (ask your winemaking supply store which products in stock are best) to juice or must to ensure the yeast have everything they need to conduct a happy and healthy fermentation.

If you’ve already got hydrogen sulfide in your wine — and if it’s there, you’ll know — you’ve got a couple of options. The first recourse is always aeration. By taking the wine through a couple of splashed rackings, it is possible that the offending odor (or most of it) will simply “blow off.” A splashed racking involves simply letting the wine splash freely as it is siphoning from carboy to carboy. This technique works especially well for red wines and for white wines that are still
fermenting, as red wines and young, unstable whites can take a lot more oxidation than finished white wines.

The second option is to add copper sulfate (COSO4) in very small amounts to bind the offending aroma and make it less noticeable or eliminate it. A word of caution, however: Copper sulfate is highly toxic in large amounts. The legal limit for wines in the United States is 0.004 grams per gallon. If you don’t like to add anything artificial to your wines, this method is one you should definitely avoid. If you choose to go that route, proceed with care. Add minute amounts of the copper sulfate liquid to each stinky barrel or carboy, being absolutely sure not to exceed a total concentration of 0.004 grams per gallon. A little more might not hurt you, but don’t take chances. The take-home message: Prevent any potential hydrogen sulfide problems from happening; don’t rely on treating them later.

Cork Taint
Cork taint, sometimes called TCA, is caused by certain types of molds naturally present on the bark from the cork trees. When these molds come in contact with any chlorine in the winemaking process,  usually from sanitizing solutions and the like, the compound trichloroanisole (TCA) can result. TCA smells different to different people, but it is usually described as being swampy, plasticy, Band-Aidy, or moldy. TCA is a very, very strong aromatic compound and can be detected readily by most people at extremely low concentrations. Though cork taint is a defect that happens rarely, it is still one to try to curtail during the winemaking process.

This is easier said than done, however. Unfortunately, the probability of cork taint showing up in your finished wines is really reliant upon the presence of these types of molds in the corks you buy. So what’s a home winemaker to do? The first line of defense would be to buy corks from a reputable producer who has been in the business for many years. This will usually mean that they’ve got a good, steady supply of corks on their end and many satisfied customers who haven’t run them out of business. Keep your corks enclosed in their storage bag in a dry, cool place. When you’re ready to use them, soak them for a short time in a strong sulfite solution (one tablespoon in two gallons of water) just before corking your bottles.

The second line of defense, and one that plays a counterpart to the first, is to try to maintain a chlorine-free winemaking environment to ensure that no contaminating chlorine compounds come in contact with the corks during any part of the winemaking process. This doesn’t mean that you can’t chloro your floors; it just means that if you use chlorine solutions for sanitizing equipment or any surface that might touch the wine or the corks, you should consider switching to TSP (trisodium phosphate) for cleaning and use strong sulfite solutions for sanitizing.

If you’ve got a corked wine, there’s really nothing you can do to get rid of it. Sometimes swirling the glass vigorously will blow off some of the aroma, but you’re really better off grabbing another bottle and hoping that this time the cork doesn’t have any of those pesky bits of mold on it. Again, cork taint is another defect that is better prevented rather than tolerated.

Experiencing the heartbreak of a spoiled bottle can be relatively traumatic for the home winemaker. You shepherd your grapes throughout a long growing season, watch them ripen, pick them with care, and then diligently watch over them as they begin the journey that will eventually land them in your wineglass. You are rightfully disappointed when something as unpleasant as acetic acid, hydrogen sulfide, or cork taint makes all of your hard work seem for naught. These defects are never 100 percent preventable, but you can employ all of these techniques to even the odds in your favor.

Issue: April 1999