August/September 2015 Keys to Grape Sampling In This Issue Lindsay Jordan, UCCE Madera, Merced & Mariposa Keys to Grape Sampling I spent many hours walking down independently. Grape Maturity and vineyard rows in the early Raisin Quality Samples should never be taken morning hours collecting grape from vines at the end of a row or samples as a winery intern. At Factors Affecting Red the rows at the edge of the Grape Coloration the time, I focused on getting my vineyard, since these vines can job done – collecting samples County Updates sometimes ripen more quickly from each vineyard block, than the rest of the vineyard Vineyard Spotlight: measuring the sugar and acid, block and this “edge effect” will Esca and reporting these values not represent your vineyard promptly to the vineyard Upcoming Events block. managers and winemakers, but I didn’t appreciate how important All sugar sampling should occur in avoid this by crushing the berry grape sampling was to the entire the cool morning, because sample in a clear plastic bag harvest operation. Every grower sampling in the heat of the day and visually checking there are knows that getting an accurate, can yield artificially high sugar no intact berries left or you can representative sample of fruit in values that will not represent the use a food mill, a piece of order to track ripening and plan actual sugar at harvest. kitchenware commonly used in for harvest is critical, but this is Sampling should be postponed if canning to separate fruit skin not an easy thing to do. there is rain, dense fog, or dew and pulp from juice. After the because this can give diluted Identify What to Sample fruit is crushed, you can decant, values. filter using a coffee filter or The first step to a successful paper towel, or centrifuge the When processing your collected maturity sampling protocol is juice to remove solids. No grapes, it is critical to ensure recognizing your own needs matter how you process your every berry of the sample is within a vineyard. It’s important grapes, always process samples crushed. Underripe fruit is harder to identify any sub-blocks that the same way if you want to to squish, but if missed during may be harvested separately, due compare results for harvest processing, the resulting juice will to different rootstocks or vine age scheduling. appear more ripe than what is or just because of logistics, and actually in the vineyard. You can to sample these blocks ...Sampling continued on page 4 ©University of California Cooperative Extension 1 Around the San Joaquin Valley County Updates Kern County Madera, Merced, & Mariposa Counties Ashraf El-Kereamy Lindsay Jordan Research projects are underway to determine the Wine grapes were being harvested in late July this best PGR treatment and pruning system for year in Madera County, so like last year, it is Autumn King and Scarlet Royal table grapes. another early start to grape harvest. The Evaluation of different rootstocks for both cultivars comparatively cool (aka not scorching hot) months is in progress as well. Higher than normal of June and July may have contributed to the populations of Glassy-winged Sharpshooters have higher than normal acid levels in juice and musts been trapped in Kern County this year. at harvest. Understanding the composition of your fruit is critical for making harvest decisions and Tulare & Kings Counties creating quality raisins and wine, so check out this Allison Ferry-Abee issue’s articles on raisin quality and on grape In September and October, keep on the lookout for sampling methods. Happy harvest everyone! symptoms of leafroll virus and red blotch virus. We are especially interested in figuring out the scope In the lab of Dr. Gubler at UC Davis, several different fungal pathogens have been identified and severity of red blotch affected table grapes in within the budwood of table grape species. the San Joaquin Valley. If you see vines with More bud samples from table grapes across the symptoms similar to leafroll, please let your farm San Joaquin Valley are needed to continue this advisor know so we can come out and take a work to better understand these infections and look. For examples of Pierce's disease and leafroll their effects on bud rot. virus symptoms, check out the UC IPM website www.ipm.ucdavis.edu/. To learn more about red If you have noticed bud necrosis or stunted blotch virus and symptoms, look at http:// shoot growth and/or have concerns about trunk iv.ucdavis.edu/Viticultural_Information/? disease in your table grape vineyard, contact uid=284&ds=351 or google "red blotch grapes" your local UC Cooperative Extension viticulture and click on the UC Integrated Viticulture site. farm advisor about collecting samples to send to Dr. Gubler’s lab for testing. Fresno County George Zhuang Raisin harvest began with Zante Currant in the last week of July and Selma Pete was ready for drying at 20-22° Brix in Parlier and a couple of locations in Fresno at the beginning of August. Ripening can be variable in different locations. For wine grapes, the harvest of Pinot Grigio and Chardonnay started during the last week of July in some areas of Fresno. The peak of harvest is upon us. Pictured: Brown rot of a grape bud ©University of California Cooperative Extension 2 Grape Maturity and Raisin Quality Matthew Fidelibus, UCCE and UC Davis Viticulture and Enology Raisin appearance, texture, flavor, moisture form finer wrinkles and a more compact shape content, and wholesomeness, are all important than tray-dried raisins and these differences may contributors to product quality. However, maturity, somewhat improve their airstream sorter grades. or the sugar content of fresh grapes at the This could be a useful benefit for DOV raisin initiation of drying, has the most dominant and growers, since DOV raisins take longer to dry than fundamental influence on raisin quality and yield. tray-dried raisins and might sometimes have less When grapes are dried on trays, berries that have than optimal soluble solids at drying. However, we amassed a sufficient quantity of solids will dry into recently showed that consumers preferred well-filled raisins having a rounded shape with ‘B and better’ raisins made from grapes having numerous fine wrinkles, or shallow wrinkles with >20 Brix at drying to ‘B and better’ raisins made thickened edges; such raisins are assigned the from berries with lower soluble solids, so grape best raisin quality grade, ‘B and better’. In maturity effects on raisin quality may extend contrast, grapes with inadequate solids will lack beyond the assignment of USDA grades. bulk and dry into raisins having a flattened, Clearly, accurate knowledge of grape maturity is angular appearance, with deep and thin wrinkles. very important for making harvest decisions. To The physical characteristics of raisins of different ensure an accurate assessment, the samples must grades enable their separation with an airstream be representative of the block to be harvested. sorter, and the proportion of raisins having ‘B and Cluster or berry samples may be used, but the goal better’ or ‘substandard’ grades are thus should always be to collect a sample that is determined. representative of the area to be harvested. In general, tray-dried raisins may meet minimum Collecting multiple samples from a block may be quality standards when made from grapes having useful to determine the uniformity of maturity > 19% soluble solids, though yield and quality will within a block. Raisin quality is generally better increase with soluble solids up to at least 22 °Brix. from blocks with good uniformity than those from In late summer, raisin grape soluble solids blocks with poor uniformity, for a given average commonly increase about 1 °Brix per week, so it soluble solids level. could take three weeks to go from 19 to 22 °Brix. Such an increase in solids can substantially improve quality and yield, but delaying drying by three weeks may substantially increase the risk of exposure to poor weather, and may not always be possible depending on labor availability. Drying method also affects the shape and surface texture of raisins and may thus influence raisin airstream-sorter grades. For example, former UC viticulture specialist Fred Jensen showed that grapes treated with a drying emulsion may form raisins with finer wrinkles than non-treated grapes, and thereby improve airstream sorter grades. Pictured: Poor quality DOV raisins, made from grapes Likewise, dry-on-vine (DOV) raisins also tend to of low soluble solids. 3 ©University of California Cooperative Extension 3 ...Sampling continued from Page 1 variation. If for example, my vineyard block has a natural swale in the middle where my vines are Understand Vineyard Variability growing much more vigorously and generating During maturity sampling, the variation within a denser canopies, this fruit will likely mature more vineyard block must be considered. Identifying slowly than the rest of the vineyard. If this denser zones of different growth or stress is critical to part of my vineyard represents 20% of the whole collecting an accurate sample. Soil types may block, then 20% of my grape berries or clusters change within a block or gravel or sand streaks can should come from that area for my maturity create regions with weaker growth. Pest and sampling. disease pressures may vary throughout the For an accurate sample, it is critical to get a vineyard causing variable growth, such as proportional sample from different areas of vine phylloxera which causes radiating circles of weak growth. growth. Younger replant vines will be smaller than mature vines. Clogged or leaking irrigation drip Choose Berry and Cluster Sampling lines may cause differences in vine growth.