Wine Grape Sampling: A Critical Step in the Winemaking Process during Harvest

Perhaps the biggest make-or-break decision made by a winemaker each vintage is deciding when to harvest the wine grapes. The chemistry of the freshly picked grapes largely determines the potential of a wine’s greatness, as well as the amount of work and attention needed in the winery to coax the wine to that elite quality level. There are multiple methods of estimating when a vineyard is ready to be harvested, and most wineries begin these estimations in the winemaking process by grape sampling–literally walking each vineyard and picking select clusters to take back to the winery for testing and tasting. Sampling begins roughly four weeks before the expected harvest date.

Wine Grape Sampling: a Pre-Harvest Winemaking Process

At Jordan Winery, we set out early in the morning armed with vineyard maps on our iPhones, a list of which blocks and sub-blocks to sample, ATVs, harvesting shears and plenty of buckets for collecting wine grape samples from each distinct vineyard block. While many wineries collect random berries to use for fruit maturity estimates, we sample whole grape clusters. Whole-cluster sampling is much more thorough and accurate because each portion of the cluster is being represented, not just a few of its grapes. Removing clusters rather than berries for sampling is also better for the fruit. Picking individual berries off a cluster that is still maturing on the grapevine can bruise the remaining grapes, causing sugary juice to leak from their skins–which provides nutrients for rot-causing microbes and also attracts pests. A simple act like removing one berry can be as damaging as a hungry bird with a sharp beak.

The grape samples collected must be representative of each sub-lot or row (as seen in three-bin photo above)–not just overall vineyard. Due to different soil types, root stocks, meso-climates, and micro-climates surrounding each part of the vineyard and even individual vines, it is important that the sampling is done with the same level of precision as the viticultural practices prescribed by the winemaker. A vineyard, for example, may be divided into many different blocks, and perhaps even sub-lots within those blocks. Because each of those sub-lots will be treated as if they are their own vineyard in regards to the picking date and winemaking process, they must be sampled individually as well. Why is this important? Simply put, different soils and micro-climates can cause different portions of a vineyard block or row to reach maturity or optimal ripeness at different times. The uniformity of grape ripeness that results from making several harvest passes through a single vineyard–only picking the perfectly mature grapes and returning a few days later for another row–contributes to the balance and finesse of Jordan wines.

Regardless of the method employed, the wine grape sampling must be random–and this is not as easy as it seems. Novice samplers tend to choose similar looking clusters from a similar portion of the plant, along the cordon or cane of each vine. It is crucial to have a system that ensures clusters from every portion of the vine–from each portion of a vineyard sub-lot–are truly represented.

The randomly selected clusters are taken to the winery and weighed to calculate average cluster weight. They are then crushed by hand the old-fashioned way. Sugar density (measured in °Brix) and seed maturity are observed at the crush deck, and samples are prepared for a more thorough laboratory testing of the grape juice acidity. These samples will also be tasted by the winemaking team before any decisions are made. Although it is nice to have the lab numbers as back up, it all comes down to taste and balance on the palate, at least for experienced winemakers like Jordan’s Rob Davis.

Typically at Jordan, we harvest our Bordeaux variety grapes (Cabernet Sauvignon, Merlot, Malbec and Petit Verdot) at lower sugar levels than is common in Northern California–levels more like the grand cru classé wines of Bordeaux that were the original inspiration for Jordan Cabernet Sauvignon.

Watch the grapes being harvested next.