When to harvest: sugar, acidity and phenolic ripeness

The harvest date is the most consequential decision of the year, and the most tempting to reduce to a single number. Sugar tells you the alcohol you will get, but it says almost nothing about whether the tannins are ripe or the aromas are there. Picking well means reading three kinds of ripeness at once — and a curve, not a spot reading.

Three kinds of ripeness

• Technological ripeness — the numbers: sugar (potential alcohol), titratable acidity and pH. Easy to measure, and the balance you are targeting in the glass.
• Phenolic ripeness — the tannins and anthocyanins in skins and seeds. Ripe seeds turn brown and woody; ripe skin tannins taste supple, not green. Critical for reds.
• Aromatic ripeness — the varietal aromas and their precursors, judged mostly by tasting berries.

In a warm climate these fall out of step: sugar can race ahead while phenolics lag, so a wine picked "on the numbers" tastes green and alcoholic. Reading all three is what stops that.

Taste the berries, not just the meter

Walk the block and taste: the pulp for sweetness and acid balance, the skin for how readily it releases colour and whether its tannin is supple or harsh, and the seeds — crunch them — for brown, nutty (ripe) versus green, astringent (not). This sensory read of phenolic ripeness is what the refractometer cannot give you.

A useful discipline: never let a single high-sugar sample trigger the pick. Confirm the phenolic and aromatic picture by tasting, and confirm the trend across at least two samplings.

Sample the block properly

• Take a representative, randomised set of berries across rows, vine positions and both sides of the canopy — not a handful from the headland.
• Sample on a schedule as ripening approaches (e.g. twice a week), so you build a curve.
• Watch the rate of change: sugar accumulation slowing and acidity flattening signal the window is near.

Read the curve, decide the date

A single sample is a data point; the curve is the decision. Plotting sugar, acidity and pH across samplings shows momentum and lets you place the pick where the numbers and the taste line up — allowing for the weather ahead and your cellar’s capacity.

To convert a refractometer reading to potential alcohol as you sample, the must weight converter does it instantly.