Grapes are a unique agricultural product. While more than half go toward the production of wine, they are also grown to be dried into raisins or eaten fresh. Grapes command more return per acre than almost any other plant, and in 2018, a single hectare of grand cru vineyard in Burgundy cost over seven million dollars on average. Further, unlike many crops that are planted each growing season, vineyards are a long-term investment—they require several years to become established and are designed to survive for decades.
Unlike many commodity plants, the profitability of wine grapes is driven by quality, which includes the grape’s ability to convey a unique sense of place. While other agricultural crops look to new varieties for flavor improvement, disease resistance, and adaptations to climate, most wine producers rely on a small number of established cultivars. Site selection and vineyard practices, however, are critical, since improvement is achieved through management of the vine’s environment.
Grapes were one of the first fruits to be domesticated by humans. In ancient times, they were prized for their high levels of sugar, a source of both nutrition and novelty. Most of the grape varieties used in wine production belong to a single species, Vitis vinifera, which was first domesticated from wild grapevines, called Vitis vinifera subsp. sylvestris (or Vitis sylvestris), at least 7,000 years ago in the land between the Black, Caspian, and Mediterranean Seas. As nomadic people settled into an agrarian lifestyle, they carried grapevines south to Mesopotamia. Domestic vinifera grapes were spread from the Fertile Crescent throughout the Mediterranean and Europe, driven by the westward migration of
"After veraison, potassium is exchanged for protons in the berries, lowering the fruit’s acidity."
Could you be more specific as to this mechanism? I understand that acids in solution will disassociate a Hydrogen atom (a plus charge), thus making the solution "acidic", but in what manner can that positively charged ion be replaced by a K+ ion? Further, The Skinkis/Schriener paper only indicates that this occurs, and that it causes greater pH (lower acidity). Since pH is a function of the number of charges, and the ions are replaced one-for-one, both carrying the same charge, it seems as if at best acidity would remain static.
During ripening, K+ is transported into the berries from the xylem in order to regulate the osmotic pressure, which helps to control the amount of water in the berries. The mechanism is an example of "cation exchange", in order for K+ to move into the cell, H+ must be removed in order to keep the overall + charge the same.
pH is not a function of the number of charges, it only depends on the concentration of H+, so when this exchange happens (and there is less H+), the pH increases.