Harvest Timing & Ripeness Assessment Philosophy

Jancis Robinson summarised the change in 2008: as grapes ripen, sugar levels rise, acid levels fall and the phenolic compounds in the grape skins (tannins, pigments and flavour compounds) evolve. WSET (2021) describes grapes that are ready to pick as having developed "the right amount of colour, flavour, acid, tannin and, importantly, sugar." The WSET Level 2 Award in Wines specification (Issue 2.1, 2026) sorts ripeness into unripe grapes, ripe grapes and extra-ripe grapes (late harvest, raisined). Writing for Decanter in 2019, Justin Howard-Sneyd MW noted that winemakers often use potential alcohol as a guide to when grapes should be picked, but that the ideal potential alcohol for a wine does not always correspond to flavour ripeness (when the grapes taste great) or to phenolic ripeness. As the grape approaches ripeness, he wrote, its phenols change from green and bitter to pleasantly astringent, to soft and ripe-tasting.

• Sugar: AWRI (2010) says sugar accumulation is generally more rapid in the weeks following véraison and usually becomes slower later
• Acid: during ripening, AWRI (2010) says malic acid in the berry is drawn upon and broken down to provide energy, and hot night-time conditions deplete it further
• Phenolics: in red varieties, AWRI (2010) says skin tannin levels are already relatively high at véraison and remain essentially constant thereafter; anthocyanins begin to accumulate in the skins about two weeks before the colour is visible
• Aroma: AWRI (2010) says the methoxypyrazines responsible for capsicum and asparagus aromas decrease as berries mature, while the terpenoids that give floral or citrus aromas increase

OSU Extension enologist James Osborne (2023) lists pH, titratable acidity (TA) and Brix as the standard grape compositional measurements, with yeast assimilable nitrogen (YAN) and malic acid sometimes measured close to picking. He calls a representative sample the first critical step: vineyard sampling should reflect the block that will be harvested and minimize bias. For red grapes he recommends crushing samples by hand in a resealable bag and letting the juice soak on the skins for a few hours in the fridge, which gives a more accurate pH because the skins contain a significant amount of potassium. Brix is typically used to estimate potential alcohol, but it is not equal to fermentable sugars, so measuring glucose and fructose gives a more accurate estimate. pH and TA are not the same, and OSU advises measuring both. Washington State University extension authors Thomas Henick-Kling and Jim Harbertson also advise tasting the skins separate from the pulp and seeds, since the majority of aroma compounds are found in grape skins, and in varieties known for vegetable aromas, such as Sauvignon blanc, Cabernet Franc, Cabernet Sauvignon and Merlot, the skin can be used to judge how ripe the fruit is.

• Sampling: OSU Extension (2023) says sampling strategies should reflect the block that will be harvested, since the more closely samples represent the grape and juice in the tank, the better
• Potential alcohol: OSU Extension (2023) gives the formula (glucose g/L + fructose g/L) / 16.83 = potential ethanol (% v/v)
• Acidity: OSU Extension (2023) says acidity affects wine microbial stability, sulfur dioxide effectiveness, color, potassium bitartrate stability and taste, and that potassium increases in the berry during ripening
• Tasting: WSU extension authors list green or grassy aromas and green seeds with lots of tannins as signs of under-ripe fruit, and advise checking fruit maturity frequently

Writing for a cool, late-ripening Washington season (page dated 2026), WSU extension authors observed that ripe flavours seemed to be developing at lower sugar content and higher acidity than usual, and said they might see ripe Sauvignon Blanc at 20 to 22 Brix, ripe Riesling perhaps as low as 19 to 21 Brix, and ripe Merlot and Cabernet near 21 to 23 Brix. The WSU authors (page dated 2026) described TA of 9 to 11 g/L with pH 3.0 to 3.2 in white must as not unusual for cool climate conditions, and expected red varieties at TA 7 to 9 g/L with pH 3.2 to 3.4. AWRI (2010) notes that in Australia sugar accumulation is often considered too rapid relative to phenolic and aroma development, likely because of high evaporative water loss from berry surfaces under dry conditions. Paul Pontallier of Château Margaux, quoted by Jancis Robinson in 2008, said grapes in most New World regions "accumulate a lot of sugar quickly and lose acidity before tannins get a chance to ripen well." For Germany, Wines of Germany states that the higher the must weight, the higher the quality or Prädikat level, and that each Prädikat has a minimum must weight depending on grape variety and region, with requirements usually higher in the southern regions.

• Cool season (WSU, page dated 2026): lower sugar at ripeness means potentially less alcoholic wines, which the authors put at 10 to 12.5% in whites and 11.5 to 12.5% in reds
• Dry (AWRI): sugar accumulation is often considered too rapid relative to phenolic and aroma development in Australia
• German must weight (Wines of Germany, accessed 2026): a must with 90 °Oe contains 209 grams of sugar per liter, which after fermentation gives 12 to 13% alcohol by volume, and quality-oriented growers tend to prefer higher starting must weights than the law requires
• Hang time (Jancis Robinson, 2008): the fashion for later picking is less about seeking more sugar and alcohol and more that winemakers have come to view the astringency associated with tannins as undesirable

A Shiraz study by the National Wine and Grape Industry Centre at Charles Sturt University, presented in the Yarra Valley in February 2015 and published on the AWRI site, harvested grapes sequentially and proposed harvest windows for fresh fruit, mature fruit and jammy fruit. The researchers found a clear aromatic difference between wines from the fresh-fruit and mature-fruit harvests, concluded that harvest date was the major driver of wine style irrespective of vineyard site and management and clone, and noted that the wineries' commercial harvest dates coincided with the mature stage. Jancis Robinson wrote in 2008 that keeping grapes on the vine is by far the easiest known way to tame tough, chewy tannins, and that producers were picking when tannins had softened as much as possible, even at the expense of much lower acidity. Pontallier warned in the same piece that high alcohol reinforces the dryness of tannins, and that added tartaric acid does too.

• Early-drinking reds: Kevin Glastonbury of Yalumba, answering in the December 2018 issue of Decanter, put picking at the desired level of balanced ripeness second on his list for softer tannins, after selecting a vineyard that produces less tannic grapes
• pH and texture: in the same answer, Glastonbury said a slightly higher pH gives a rounder, softer mouthfeel
• Correcting the balance: Jancis Robinson (2008) notes that in most wine regions tartaric acid may be added when grape acid is too low, and in many regions water may be added or technology such as the spinning cone used when alcohol is too high
• Beyond ripe: André van Rensburg of Vergelegen, quoted by Jancis Robinson in 2008, said "after greenness comes ripeness, then overripeness, and then dead fruit."

A study of Beaune harvest records back to 1354, reported by Decanter in 2019, found that from 1354 to 1987 grapes were on average picked from 28 September, while in the 31-year period of rapid warming from 1988 to 2018 harvests began 13 days earlier. The researchers also found that the most outstanding heat and drought years were not necessarily the earliest harvests, concluding that grape development slowed down or even stopped during very long rainless periods and extreme maximum temperatures, as in 1540 and 1473. For a late season, WSU extension authors warned of a possibly compressed harvest with tight tank space and advised winemakers to be ready to harvest at lower than usual sugar content. AWRI (2010) notes that the growth of Botrytis is favoured by sugar accumulation in berries, and that berry cell walls weaken as fruit matures, increasing susceptibility to bunch rotting fungi such as Botrytis.

• Uneven ripeness (WSU): taste the fruit in the vineyard for large variations in ripeness, and if possible harvest and ferment fruit of different ripeness separately
• Lagging clusters (WSU): clusters lagging behind in ripening were dropped at véraison, and these late clusters will not catch up to the maturity of the earlier clusters
• Sorting (WSU): hand-harvested fruit can be sorted at the winery to separate less ripe fruit for a separate fermentation
• Frost-dependent styles (Wines of Germany, accessed 2026): ice wine is harvested when it is at least minus 7 degrees Celsius and is becoming more of a rarity as Germany experiences warmer winters

Wines of Germany describes Kabinett as fine, light wines from ripe grapes with low alcohol content, and Spätlese as ripe, elegant wines harvested a little later, more intense in flavour and concentration but not necessarily sweet. For Auslese, unripe berries are separated out. Beerenauslese is made from individually selected, overripe berries usually infected by Botrytis cinerea (noble rot), harvested only when exceptional weather lets the grapes ripen that far. Trockenbeerenauslese, the top of the quality pyramid, comes from shrunken, shriveled, noble rot berries that cannot be harvested every vintage. Must weight is measured in degrees Oechsle, named after the Württemberg pharmacist and mechanic Ferdinand Oechsle, and Wines of Germany (accessed 2026) notes that Beerenauslese musts of 120 °Oe or higher reach sugar concentrations of over 300 grams per liter.

• Kabinett (Wines of Germany): fine, light wines from ripe grapes with low alcohol content
• Spätlese (Wines of Germany): harvested a little later; more intense in flavour and concentration, but not necessarily sweet
• Auslese (Wines of Germany): from fully ripe grapes, with unripe berries separated out
• Enrichment (Wines of Germany): quality wines may be enriched (chaptalised) with a legally limited amount of sugar before fermentation; Prädikat wines may not

Primary sources: https://extension.oregonstate.edu/crop-production/wine-grapes/preparing-harvest-grape-chemistry-pre-fermentation-adjustments, https://wine.wsu.edu/late-ripening-how-to-deal/, https://www.awri.com.au/wp-content/uploads/5_phenology_berry_development_ripening_3.pdf, https://www.awri.com.au/wp-content/uploads/2015/02/Berry-ripening_5_2_14.pdf, https://www.winesofgermany.com/our-wine/quality-standards/quality-standard/449/pr%C3%A4dikat-categories, https://www.winesofgermany.com/our-wine/quality-standards/quality-standard/182/must-weights, https://www.wsetglobal.com/knowledge-centre/blog/2021/june/22/the-lifecycle-of-a-vine/, https://www.wsetglobal.com/media/19132/wset_l2wines_specification_en_april2026_issue21.pdf. Last verified 2026-09-28