Dealing with Harvest Challenges
From a viticultural and winemaking perspective, it has thus far been an exceptional year in more ways than we have expected or predicted. Blame it on climate change, El Niño, or star alignment, but many are faced with pre-harvest weather extremes in many parts of North America from downpours to scorching heat and high humidity causing all kinds of challenges in the home winery.
I have already started receiving messages from distraught winemakers asking how to rescue their stuck fermentation, how to deal with mold, or what’s with the fermentation off-odors—the result of grapes starting to ferment prematurely.
If you have not harvested yet and expect heavy or prolonged rainy periods, you should consider harvesting before the rain; you can always adjust sugar and acidity in the winery. Heavy rainfall can cause berries to start splitting, to grow mildew, and possibly indigenous yeasts to kick-start the fermentation resulting in off odors and flavors and quite possibly spoilage.
If you have been hit by heavy rain and berries are splitting or spoiling, harvest and crush as quickly as possible making sure to add a good dose of sulfite based on the amount of spoilage; at a minimum, add 50 mg/L (ppm). This may cause problems if you intend on a malolactic fermentation, in which case you should consider double-salt precipitation to reduce what is likely high malic content. (I discuss double-salt precipitation techniques in the upcoming Oct-Nov issue of WineMaker.) And don’t forget to add yeast nutrients. Yeast will be struggling and yeast cells will therefore need lots of nutritional food to grow and reproduce to ferment properly.
At the other end of weather extremes, like in the northeastern US and Niagara regions where vineyards were blessed with a superb growing season—though not without its challenges of excessive heat or mold—harvest is well ahead compared to previous years. Some have begun harvesting.
Here, the problem is high sugar and low acidity. Again, be sure to add sufficient yeast nutrients as yeast cells will be struggling here too in the sugar-rich environment. As for low acidity, there will be considerably less malic acid, which can be compensated by adding tartaric acid BEFORE fermentation. And add at least 25 mg/L of sulfite or more depending on the condition of the grapes. Then keep a watchful eye on the fermentation to make sure it progresses well and does not become stuck.
What is important here is to stay on top of fermentation. Do regular punch-downs. Monitor Brix consumption. Smell the fermenting must to spot any off odors or other signs of a problem fermentation. Keep open fermenters under a heavy tarp. And keep fruit flies away—they carry acetic acid bacteria that can cause bacterial infection and spoilage.