Grape harvest is underway in the southern part of the state and has recently started in the Lafayette area. Most varieties are slightly behind normal this year. We generally harvest early varieties such as Brianna, Edelweiss and Prairie Star about the third week of August and many other early varieties starting the first week of September. Lately, the weather has been good for fruit ripening, as cooler conditions will improve fruit quality. A bit of both powdery and downy mildew are present on leaves, but overall fruit quality looks great. Recent rains did not cause fruit cracking so fruit rots are minimal.
Wine grape growers should have the ability to measure sugar content (with a refractometer), titratable acidity and pH (with a pH meter and burette). Equipment and supplies to measure these parameters can be purchased for about $500-1,000. Each of these factors is important for determining proper harvest time, but none alone can accurately estimate overall fruit quality. It is the balance of sugars, acids and juice pH that is important to the winemaker. And of course, there are the subjective qualities of seed and skin maturity, tannins, anthocyanins, flavors, aromas, etc. The Berry Sensory Analysis method addresses the evaluation of these more subjective factors such as skin, pulp, and seed maturity. More needs to be done to adapt the method for use with our Midwest varieties, but as a descriptive tool, it can be an excellent way for growers to go beyond the basics of sugar, acid, and pH. Work with your winemaker/buyer on harvest decisions as much as possible.
As you go about harvest, it’s good to troubleshoot. Birds, raccoons, deer, turkeys, etc. can all take a toll. More importantly, berry skin cracking from rain, bird pecks, and bee damage can lead to sour rot caused by yeasts and vinegar spoilage bacteria. The vinegar (acetic acid) leads to high volatile acidity levels in the wine. We experience major problems with sour rot in wet years. The lack of rain recently means that we have not had any problems this year. Let’s hope the weather continues to cooperate. Growers need to closely monitor for development of sour rot, especially if rains occur near harvest, and take measures to reduce the spread by managing fruit flies and microbial organisms. Ultimately it may be necessary to develop a strategy to minimize harvest of rotted clusters. A pre-harvest walk through the vineyard block should identify any clusters with sour rot and those lagging in ripeness. In most cases, late clusters will never catch up to the rest, and will only reduce the overall quality of the crop at harvest. Pre-harvest is a good time to drop any undesirable fruit. Don’t expect your harvest crew to sort as they pick. Go through beforehand and eliminate the guesswork.