Sampling

sampling, important part of a continuum of wine quality control procedures which begin in the vineyard and may end when a consumer picks a bottle out of a case in his or her cellar.

A very small proportion of a vineyard’s fruit may be sampled to assess its chemical composition to help predict the harvest date, as well as to indicate likely quality and, in some cases, eventual wine style. Grape sampling might simply consist of selecting some berries haphazardly from the vineyard and expressing juice into a refractometer to measure sugar content (see must weight; see also ripeness). A more rigorous approach involves larger samples and winery laboratory analysis.

Vineyard sampling has become far more focused since the turn of the century, thanks to precision viticulture and to research into grape composition and wine quality. Both approaches make it much easier to keep together batches of fruit that have similar quality potential, sometimes referred to as streaming when the fruit is fermented together in large vats. However, many vineyards are harvested without a fruit sample being taken, particularly in more traditional regions.

The person taking the sample must be careful to avoid any bias which might affect the sampling result. Either berries or bunches are taken, and a normal sample may weigh 300 g (10.5 oz) to several kilograms. Typically the sample is crushed or pressed in the winery to obtain juice, which is then analysed for sugar and typically also acidity and ph. Some modern laboratories use spectrophotometry or near infrared spectroscopy (NIRS) to analyse the concentration of extractable anthocyanins. Spectrophotometry can also determine the total phenolic compounds in the grapes. The total extractable anthocyanin value has been shown to correlate well with the potential wine quality. See also physiological ripeness.

A second sampling is frequently made when a load of grapes is delivered to the winery, particularly if the grapes have been bought by contract, since grape prices are often based on grape composition, typically on sugar levels.

During fermentation samples are taken at least daily to verify the regular conversion of sugars to alcohol. Later, during élevage, regular sampling provides the winemaker with valuable guidance. Finally, shortly before bottling, samples are taken for detailed analysis to ensure that the wine meets all regulations and is free of faults and contaminants.

An important part of selling wine en primeur is the release of cask samples, or échantillons in French, samples drawn from the containers in which the wine is still being matured, typically a barrel, on which wine merchants and wine writers can base their assessments. Such raw wines, often roughly drawn off into small sample bottles, have not undergone stabilization and can suffer oxidation and other faults after only a week or two. The best way to judge a young wine still in cask is sampling in the cellar or winery itself, tasting it straight from the barrel, but sampling the contents of a wide range of different barrels.