Hi Lauren, great question. There are so many steps along the way where a fermentation can get into trouble, or “go pear shaped” as my interns from New Zealand used to say. We could almost do a walk through from start to finish, or even picking to dryness and say well, it could go south on you at this point, here, here, and here . . . but then we might get discouraged and never make wine again.
For home winemakers, I think there are two common fermentation problems that tend to crop up the most: Proper yeast nutrition and fermentation temperature control. It’s relatively easy to measure the “big numbers” like Brix (sugar content/soluble solids by density) and even pH and total acidity. Those are all pretty inexpensive analyses to do for any home hobbyist who wants to do a little wet chemistry and play mad scientist in their own little home lab.
The harder analyses to do are those like amino acid analysis and nitrogen content for nutrition, for which commercial wineries or wine labs spend thousands of dollars on specialized lab equipment. A home winemaker either has to carry her juice sample (quickly!) to a chemistry-for-hire wine lab or they have to make a really, really good guess as to what the nutrient status of that juice or must is. When taking a stab in the dark, it’s probably advisable to add a little complex yeast nutrient (like “Superfood” or similar) in order to cover any missed bases. Taking this approach, a home winemaker runs the risk of over-feeding and subsequent residual nitrogen post dryness, which can continue to feed spoilage organisms later. Perfect, it ain’t. You can see why this is such a challenge.
Controlling fermentation temperature, so important to yeast health during fermentation (too hot and they get cranky, too cold they slow down) and wine quality (too hot and delicate aromas get blown off), is another tough thing for micro-producers to manage. Commercial wineries with big stainless steel fermentation tanks rely on circulating glycol systems and cooling jackets or big refrigerated rooms for barrel storage. It’s difficult, not to mention expensive, to have any kind of cooling system on a small scale. Add to this the fact that barrel fermentations notoriously get too hot (wood is a good insulator) and cause stressed-out yeast to excrete stinky hydrogen sulfide off-aromas and you can appreciate how fiddly it is.
Some home winemakers cool down must ferments by freezing gallon water jugs and tossing them (closed tightly) into fermenting totes, bins or trash cans of must during a punchdown. They then simply remove the jugs before the must gets too cold. If your nighttime temperatures are cold enough during harvest (or if you use frozen must) you could take advantage by rolling out your fermenting barrels or containers for a chill on the back porch. I recommend placing your fermenters on a cart with lockable wheels or even on a pallet, which you could then pallet-jack around carefully. Heating is a tad bit easier; many of us have warmed up the odd barrel or carboy with a heating pad or heating blanket. For small stainless steel tanks I’ve even taken a space heater and blown warm air on the surface for a while. The key is that for any of these above strategies you really have to monitor the temperature of your fermentation in order not to arrest or over-accelerate a fermentation.
In the “Wine Wizard” column, I really get a variety of inquiries. Many are of the “Oh no, I think I added too much of X” (usually acid or sulfur dioxide) type. Others are what I’ll call the “mystery goo” category where I’ll be asked to do my best to diagnose a strange ring, growth, film or mold on someone’s carboy or barrel. Another category of questions is what I’ll call the “life stage of a wine” question where someone will ask how long they should age their wine in a barrel, or when they should rack their particular kind of wine. As with all “Wine Wizard” questions, it really helps me if the question is as descriptive as possible to the situation: What kind of wine are you making, any initial chemistry if you know it (Brix, pH, TA, etc.) and any strange circumstances leading up to your problem. Of course, if any of you home winemakers run into any of these problems, or have other questions, send them (and a picture of the problem if you can) to me at
[email protected]. Happy fermenting!