Phenolic Ripeness

The always eagerly anticipated harvest season has begun, and for the following weeks, the attention of everyone and anyone with an interest in wine turns to the picking, processing and vinification of grapes into wine. With that comes a lot of talk about ripeness – and for the most part, this will generally refer to the sugar ripeness of the grapes, which is broadly used as in indicator of when they are ready to pick.


But beyond the sugar levels as an indicator of ripeness, there is also something called phenolic ripeness (also referred to as physiological ripeness), which is equally as important as sugar ripeness.


So, what is phenolic ripeness? Phenols are a type of complex molecule and include – but are not limited to – things like tannins. Phenolic compounds are found mainly in the skin, pips and stems of the grape bunches. As the grape ripens, the skin changes colour (from green to red for red varietals, or from an opaque grass-green to a slightly translucent yellowish green for white varietals).


The phenolic compounds in the skins, pips and stems also ripen, changing from bitter and astringent to softer, with a more rounded, ripe taste. This is as a result of a decrease in methoxypyrazine, which decreases the herbaceous, “green” taste in the grapes. If the grapes have achieved phenolic ripeness at the time they’re picked, the tannins in the resulting wine will be supple, rounded and pleasant.


The importance of phenolic ripeness is especially relevant to warmer winemaking regions (including South Africa), as phenolic ripeness usually trails sugar ripeness. This means in warm climates, the sugar ripeness in the grape berry indicate the grapes are ready to pick, but the physiologically the grapes are not entirely ripe yet.


At Oldenburg, we have the advantage of cooler night-time temperatures, which allows a slow-down in sugar ripening and allows the phenolic ripeness to develop and align. For Nic, phenolic ripeness is the precise moment when all the important elements of acidity, sugar ripeness and tannins are perfectly balanced. Grapes can be tested in laboratories for sugar levels, with potential alcohol levels determined, etc. – but a human assessment is required to make the call on phenolic ripeness. When he tastes the grapes, he looks at the colour of the pips, and the intensity of colour on the grape skins. The pips are a crucial element to consider in determining phenolic ripeness – Nic looks for darker brown pips, rather than green astringent ones.


When this perfect balance is reached, it is time to harvest, and the grapes begin their journey into becoming the next stellar vintage.

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