William Nail, The Connecticut Agricultural Experiment Station
Fruit sampling is done for several reasons between veraison and harvest. While it is frequently used to plot the development of maturing fruit, its most important use is to determine when fruit is ready to harvest. The goal is to obtain a sample that is as representative of the final must as possible, within the inevitable time constraints of the hectic harvest season. In order to ensure accurate sampling, it is vital to collect samples that are sufficiently random and that are large enough to be representative of the entire harvest. Therefore, samples should never be collected from exterior vines (border rows or end vines), and should always consist of multiple berries or clusters.
Many factors influence the relative maturity of fruit within a vineyard block. Berries exposed to sun tend to mature sooner than shaded berries. Exposure is determined by a cluster’s position on the vine and the position of individual berries within a cluster. The position of clusters on a shoot can also influence maturity. Basal clusters develop earlier and are usually more mature on a given date than distal clusters. Fruit that receives morning sun, but is shaded in the afternoon (such as eastern-oriented fruit on north-to-south rows), will not experience the same environmental conditions as similar fruit on the western side of the same vine, and will mature more slowly. Ideal fruit samples include berries or clusters from all positions and orientations.
Sampling can either be done from individual berries or whole clusters. For berry sampling, a minimum of 100 berries is desirable. A minimum of 20 clusters is required for cluster sampling. Berry sampling is usually more time-consuming than cluster sampling. But, if the berries are counted, berry sampling can provide an estimate of average berry weight, which is an important factor for estimating and determining the components of yield. Berries on whole clusters may be counted as well, but counting all the berries on 20 or more clusters rapidly becomes tedious.
Unless one is dealing with small test plots that have different cultivars in adjacent rows, the inherent human tendency toward lack of randomness may be largely overcome using proper sampling technique. Select adjacent rows that seem representative of the given vineyard block. Beginning at the third vine (or more) from the row end, select a leaf in or near the fruit zone at random. Collect your sample from the cluster nearest that leaf. Next, look down the opposite row approximately 20 feet and focus on a similar leaf. Sample the cluster closest to that leaf. Repeat alternating sides of the aisle until you have collected an adequate sample. Collecting the same number of samples from representative rows will increase the accuracy of your total samples. Do this for several pairs of rows if the block varies significantly in soils, typography, or other factors that may affect vine growth. Observation and experience are the best guides for determining how many areas of a vineyard should be sampled.
For berry sampling, differences in berry position within the clusters can largely be accounted for by harvesting in the following manner (Try not to think about the horizontal position of the initial berry – randomness is key.):
Make sure all berries are fully crushed before analysis, as various parts of individual berries also differ in composition. Lastly, always compare the results from your fruit samples with the must. If the results are never well-correlated, it indicates a lack of randomness or too small a sample size. However, if the results consistently differ but differ in a predictable manner, you should be able to adjust your values as necessary and have sufficient information to make informed decisions in the vineyard and winery.
Using a Refractometer, Cornell University
Reviewed by William McGlynn, Oklahoma State University and Ed Hellman, Texas AgriLife Extension