Wine Grapes

Two commodities under one crop is the correct model here because the buying criteria have almost nothing in common. A table-grape buyer wants large, evenly coloured, firmly attached berries on a presentable bunch, and will reject a lot on cosmetic grounds alone. A wine-grape buyer wants a defined sugar-to-acid balance, a workable pH, ripe tannins, and clean, undamaged fruit — and would happily take a bunch a supermarket would never display. Wine cultivars typically carry smaller, thicker-skinned berries with a higher skin-to-pulp ratio, which is a defect for eating and an asset for extraction.

Grapes are non-climacteric: sugar accumulation stops when the bunch leaves the vine. Because of this, the harvest date is the winemaking decision that cannot be revisited. Growers and winemakers track sugar concentration as it rises and acidity as it falls through ripening, and pick at the point where the two are in the balance the intended wine style requires — earlier for lighter, higher-acid wines, later for riper, higher-alcohol styles.

Sugar alone is an incomplete guide. Phenolic or physiological ripeness — the state of tannins in the skins and seeds, and the development of colour and aroma compounds — advances on its own timetable, and a lot can reach target sugar while its tannins remain harsh. Ripeness assessment is therefore a composite judgement made on sampled fruit, and it is why the same block can be picked on different dates for different wines.

Wine grapes are picked either by hand, as whole bunches into small containers, or by machine, which shakes berries free of the stems and delivers loose fruit and juice. The choice affects what arrives: hand picking allows whole-bunch handling and selection, while machine harvesting is faster and enables night picking, but breaks more skins. Both routes are designed around the same objective — get the fruit to the winery before its composition changes.

Broken skins start the clock. Once juice is exposed it oxidises and wild fermentation and acetic spoilage can begin, so damaged fruit deteriorates far faster than intact fruit. Night and early-morning harvesting is common precisely because cooler fruit slows these reactions during transport. Fruit that sits too long in a warm bin before crushing arrives at the winery as a different commodity from the one that was picked.

Wine grapes are typically bought on contract between a grower and a winery rather than traded on an open spot market, and payment terms commonly reference measured composition at delivery alongside weight, sometimes with yield caps or block-level provenance conditions attached. Regional appellation and geographical-indication schemes may further restrict which cultivars, areas, and practices qualify — these are legal frameworks around the commodity, and they are jurisdiction-specific.

• Broken and split berries — the entry point for oxidation and spoilage organisms
• Bunch rot and sour rot — decay that carries directly into the fermenting must
• Raisined or shrivelled berries — desiccation shifting sugar and yield
• Excessive material other than grapes — leaves, stems, and debris from machine harvesting
• Delivery delay and heat in the bin — composition changing before the crusher