Vintage — One season. Frost in April, mildew in July, rain at harvest.

You are the vineyard manager / winemaker. A year in a vineyard, from pruning in the winter to the last block picked. Every decision has a date and a consequence: prune late and dodge the frost at the cost of ripeness, remove leaves and cut botrytis at the risk of sunburn, wait one more week for phenolic ripeness and lose the crop to rain. At the end you get a score, a price, and a tasting note assembled from the numbers.

Timescale: one season. Model: Degree-day phenology with a soil-water bucket, weather-driven disease indices and a ripening model

What you will learn

• Why a vineyard is pruned late in a frost-prone site, and what that costs.
• Why sugar and phenolic ripeness are not the same thing, and why the gap decides the picking date.
• How a spray programme actually works: intervals, rain wash-off and pre-harvest intervals.
• Why the same weather makes a great vintage in one place and a disaster in another.

Scenarios

• Sandbox — One season, any site, any variety, nothing scored.
• Frost Year — Inspired by Burgundy 2021: a warm March, then hard frosts in April.
• Wet Harvest — The fruit is nearly there and the forecast is four days of rain.
• Heat Dome — Inspired by the Pacific Northwest, 2021: 45 °C in late June.

What you control

• Cultivar — Sets when the vine wakes up, how long it takes to ripen, and what it is trying to be.
• Region — The weather generator’s monthly statistics, and how much of a frost and heat risk the site carries.
• Soil water-holding capacity (mm) — How much water the root zone can hold. A shallow soil stresses the vine early — which is often what you want, until it is not.
• Pruning date (day of year) — Late pruning delays budbreak by up to a fortnight, which is the cheapest frost protection there is — and costs you the same fortnight of ripening in the autumn.
• Buds left at pruning (buds/vine) — This is where the crop is decided, six months before you see it. More buds means more fruit and slower ripening.
• Frost protection — What runs on a frost night. Each has a different failure mode.
• Irrigate below (% of capacity) — Soil moisture at which irrigation runs. Zero means dry-farmed. A mild deficit after véraison concentrates the fruit; a severe one stops ripening altogether.
• Spray interval (days) — Zero is no programme at all. Fourteen days is conventional; a wet season needs ten.
• Fungicide — Contact products sit on the surface; systemics are taken into the leaf.
• Leaf removal (fraction of fruit zone) — Opening the fruit zone dries the clusters and cuts botrytis — and exposes them to the sun, which in a heat wave burns them.

Questions

Why can I not just wait for higher Brix?

Because everything else is moving too. Acidity is falling, pH is rising, the berries are shrivelling, botrytis is waiting for the next rain, and the phenolics may or may not have caught up with the sugar. Picking is choosing which of those you mind least.

What is the difference between sugar ripeness and phenolic ripeness?

Sugar accumulates in the pulp and tracks the leaf area feeding each berry. Phenolics — tannins and colour in the skins and seeds — develop on their own schedule, driven by warmth and light and slowed by a heavy crop. In a hot year the sugar runs ahead and you pick a wine that is alcoholic and green; in a cool one the phenolics never arrive at all.

Why did my spray fail?

Most likely rain. A contact fungicide sits on the surface and washes off after about 20 mm; a systemic one is taken into the leaf within a few hours and survives. And both have a pre-harvest interval you are not allowed to break.

What this model cannot do

• One average vine per block. Real vineyards vary hugely within a block, and the variation is often larger than the differences this model is about.
• Weather is generated from monthly statistics with day-to-day autocorrelation. It has no fronts, no real diurnal structure and no orography.
• Disease is an index, not an epidemic model: no inoculum carry-over between seasons, no resistance, no cultivar-specific susceptibility beyond cluster tightness.
• The tasting note is assembled from the numbers by a lookup. It is a way of reading the chart, not a sensory prediction.
• Prices are a smooth curve against quality. Real wine prices depend on a brand, a region and a market, none of which are here.
• Nothing here is agronomic advice, and the spray model in particular is a caricature. Follow the label.

Sources

• Winkler, A. J. et al. (1974), General Viticulture — degree-day regions and the phenological framework
• Allen, R. G. et al. (1998), FAO-56 Crop evapotranspiration — the ETc = Kc × ET₀ water balance
• Gubler, W. D. et al. (1999), Powdery mildew risk assessment index
• Snyder, R. L. & de Melo-Abreu, J. P. (2005), Frost Protection: fundamentals, practice and economics — why wind machines need an inversion and sprinklers need continuity
• Coombe, B. G. & McCarthy, M. G. (2000), Dynamics of grape berry growth and physiology of ripening
• Sadras, V. O. & Moran, M. A. (2012), Elevated temperature decouples anthocyanins and sugars in berries — the sugar–phenolic gap this model is built around