Harvest Timing: When to Pick and What to Measure
Harvest Timing: When to Pick and What to Measure
The timing of harvest is the most important decision in winemaking. Earlier than ideal and you lock in harsh, herbaceous, underripe character that no cellar technique will fix. Later than ideal and you lose acidity, risk botrytis or autumn rains, and produce overripe, flabby wines. The window is often narrow — sometimes just days.
The Key Measurements
Brix (sugar)
Measured with a refractometer (in the field) or hydrometer (in the winery). Indicates sugar concentration and therefore potential alcohol.
Limitations of Brix alone: Brix tells you sugar content but not acid content, not pH, not tannin ripeness. A grape can be at perfect Brix with completely unripe tannins (green seeds, harsh astringency). Always use Brix alongside other measurements.
pH
Measured with a calibrated pH meter. Determines acid strength, SO₂ effectiveness, microbial stability, and colour stability.
Trend during ripening: pH rises steadily as ripening progresses. Each day of warm, sunny weather in late season raises pH further. In hot climates or warm vintages, pH can spike dramatically late in the season.
Critical threshold: pH above 3.7 at harvest means significant sulphite and stability challenges. Above 4.0 means the wine will be very difficult to protect and stabilise.
Titratable Acidity (TA)
Measured by laboratory titration. Indicates total acid concentration.
Trend during ripening: TA falls as ripening progresses — malic acid is respired (consumed) by the berry. In warm weather, malic acid destruction is rapid. In cool weather, it's slow, maintaining higher TA at the same Brix.
Physiological (phenolic) ripeness
This is the non-chemical assessment — the one that the numbers alone can't capture.
Berry flavour: Taste a berry from multiple vines and locations in the vineyard. The juice should taste of ripe fruit appropriate to the variety. Any green, herbaceous, or unripe character means the fruit is not ready.
Seed colour and texture: Ripe seeds are brown, not green, and they crack audibly when bitten with a crunchy, slightly bitter-sweet flavour. Green seeds are full of harsh, unresolved tannin — they taste astringent and bitter in an unpleasant way.
Skin texture and tannin: Separate a berry skin and chew it. Ripe skins release colour easily and the tannins feel soft or velvety. Underripe skins feel chewy, harsh, and astringent.
Stem lignification: Are the stems brown and woody? Or still green? Green stems in whole-cluster fermentation produce vegetal, harsh tannins.
Sampling Protocol
A harvest decision should be based on statistically representative sampling across the entire block — not a handful of berries from the easiest vine to reach.
Minimum protocol:
- 100–200 berries from at least 20 vines
- Sample randomly across the block — inside and outside rows, top and bottom of slope, different vine vigour zones
- Sample from multiple positions on each vine — top bunches, bottom bunches, inside the canopy, outside
- Pick individual berries from different parts of each bunch (shoulders, middle, tip)
Pool all berries in a ziplock bag. Crush by hand, strain through a cheesecloth, and measure the pooled juice. This average is more reliable than sampling one vine.
Variety-Specific Harvest Targets
| Variety | Brix | pH | TA (g/L) | Seed colour |
|---|---|---|---|---|
| Chardonnay (sparkling) | 18–21 | 3.0–3.3 | 8–10 | Light brown |
| Chardonnay (table) | 22–24 | 3.2–3.5 | 7–8.5 | Brown |
| Sauvignon Blanc | 21–24 | 3.1–3.4 | 7–9 | Brown |
| Riesling | 20–24 | 2.9–3.4 | 7–10 | Brown |
| Pinot Noir | 22–25 | 3.3–3.6 | 6–8 | Brown-dark |
| Cabernet Sauvignon | 24–27 | 3.4–3.8 | 5.5–7 | Dark brown, crunchy |
| Syrah/Shiraz | 23–26 | 3.4–3.7 | 6–8 | Dark brown |
| Merlot | 23–25 | 3.4–3.7 | 5.5–7 | Dark brown |
These are guidelines, not absolute rules. Vintage variation, site, and style target all affect the optimal window.
Decision Factors Beyond Chemistry
Weather forecast
A week of warm, dry weather extends your harvest window — you can afford to wait for more physiological ripeness. Rain predicted in 4 days narrows it dramatically. Heavy rain at harvest dilutes sugar, raises pH, and creates disease pressure.
Disease pressure
Botrytis grey rot spreads in wet conditions after veraison. Once grey rot is spreading through a block, every day of delay means more losses. Sometimes you pick early because waiting means losing 20% of the crop.
Winemaking style target
A Chablis-style Chardonnay needs high acid and low Brix. A California full-bodied Chardonnay needs lower acid and higher Brix. Your stylistic intention shapes your harvest target.
Picking logistics
Harvest requires a crew, equipment, and winery capacity. You can't always pick on the ideal day — sometimes you pick 2 days early because that's when the team is available. Factor this into your planning.
Harvest by Block
Different parts of a vineyard ripen at different rates:
- North-facing rows ripen later than south-facing
- Vines at the bottom of a slope may be 1–2 weeks behind the top
- Shaded interior rows ripen later than exposed exterior rows
- Some varieties ripen 2–3 weeks apart even in the same vineyard
Sample each block or section separately and harvest each at its own optimal moment. Never assume the whole vineyard is ready at once.
After the Decision: Moving Fast
Once you've decided to pick, move quickly. Grapes deteriorate in hot weather — pick in the cool morning, process immediately. Avoid delays between picking and pressing (especially for whites). The pick-to-press time for premium white wine production at many estates is under 4 hours.
Have your winery ready before harvest begins: clean, sanitised fermenters, presses, pumps, and all equipment checked. There is no time to fix equipment problems on harvest day.
Tip: Start your daily sampling 3–4 weeks before your expected harvest window. The data curve — watching Brix rise and TA fall each week — is far more informative than a single point-in-time measurement. And logging it in MakeWine gives you a reference for future vintages.