Harvest decision after a heatwave: high sugar, low acid and sour rot
A 6 ha Xynisteri block at 650 m, trained VSP, is due to be harvested for a dry white wine. On 20 August, grapes were at 19.5 Brix, TA 6.8 g/L, pH 3.25. From 25 to 31 August, maximum temperatures were 38-40 C with warm nights. On 1 September, samples from the block average 23.8 Brix, TA 4.9 g/L, pH 3.55. About 12% of bunches on the eastern rows show sour rot, with vinegar smell and Drosophila activity; berries are shrivelled. The winery will accept a maximum of 8 tonnes per day and wants fruit at 21-22 Brix and pH below 3.4. The crop is estimated at 42 tonnes. A 15 mm rain event is forecast for 4 September. Picking is manual with 12 pickers, and the winery is 45 minutes away.
1. Decide the harvest timing and order, and explain how you would handle the gap between fruit condition and the winery specification. Show your calculations.
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The numbers first. 42 t at 8 t/day is 5.25 days, so at least six working days, but the fruit is already at 23.8 Brix, above the 21-22 target, and rain is due on 4 September.
Do not wait for a lower Brix; it will not come. Sugar will rise further, TA is already 4.9 g/L and pH 3.55, and 12% sour rot means volatile acidity is climbing. Every extra day costs quality.
Sequence by risk, not by block order. Harvest the eastern rows with sour rot first, at night so fruit stays below 20 C, on 1-2 September, and keep that fruit as a separate lot or reject it after sorting. Then harvest the clean rows on 2-3 September so picking finishes before the rain. If the team cannot finish, harvest early rather than harvest wet fruit.
The specification gap. pH 3.55 is above the winery's target of 3.4. Acidify the must with tartaric acid within the legal limit (about 1.5 g/L expressed as tartaric acid under EU rules) rather than adding water, which is illegal. Blending with a lower-Brix parcel is an option only if one exists. 23.8 Brix will give roughly 13.5-14% alcohol, acceptable if the fermentation is controlled.
Logistics: night picking, 15-20 kg crates, fruit shaded in the field and delivered within the hour.
2. Describe the post-harvest handling and winery reception measures needed to protect quality and stay within the rules, given the heat damage and rot.
Read the worked answer
In the vineyard. Sort in the field: remove rotten bunches and leaves rather than sending them to the winery. Use small, shallow crates to avoid crushing, do not fill trailers deep, and shade the load. Warm fruit loaded at 30 C will arrive damaged even after a 45-minute trip.
At reception. Cool quickly to 12-15 C, sort again on a table, press whole bunches or after a short skin contact, and protect the juice from oxygen with inert gas or dry ice. Add 30-50 mg/L SO2 at reception and settle with pectolytic enzymes. Measure volatile acidity and gluconic acid: if either is high, the rotten lot must not be blended with clean juice.
Compliance. SO2 additions must stay below the legal maximum total SO2 (150 mg/L for red, 200 mg/L for white and rose, with higher allowances for sweet wines), and every addition must be recorded. Label contains sulfites above 10 mg/L.
Sanitation. Fruit flies and acetic acid bacteria follow the fruit. Wash crates, remove waste daily and keep the reception area clean. Temperature, oxygen and SO2 are the three levers that decide whether heat-damaged fruit becomes a sound wine or vinegar.