September 18: Forty-Five Millimetres and One Crew
September 18. The forecast shows 45 mm of rain in about 60 hours, followed by dry, warm weather. Two blocks are still hanging.
Block A - Merlot, 4.2 t/ha, 24.6 °Brix, pH 3.86, TA 4.9 g/L, 62 days since colour change, seeds brown, tight bunches already showing about 3% botrytis. This fruit is contracted at a premium for a single-vineyard bottling.
Block B - Cabernet Sauvignon, 6.8 t/ha, 23.4 °Brix, pH 3.52, TA 6.8 g/L, seeds still green with harsh tannin, loose bunches, clean.
You have one picking crew of eight (about 6 tonnes a day), a crush pad that can process 20 tonnes a day, and tank space for two more lots.
1. Set the picking order and defend it against the forecast. What would you be watching in Block B while Block A comes in?
Read the worked answer
Pick Block A first. Today and tomorrow, before the front.
The case against holding A:
- pH 3.86 is already the problem, not the sugar. Rain drives potassium uptake into the berry, and potassium exchanges for hydrogen ions - pH climbs further, and it climbs fast. A 3.86 Merlot can land near 4.0 after 45 mm, which is a stability and microbial risk, not a stylistic one.
- 3% botrytis is a live infection, not a warning. Merlot's tight bunches hold water in the interior; 45 mm plus warm, humid air afterwards is ideal sporulation conditions. Waiting converts a sorting problem into a vineyard loss.
- The contract. Single-vineyard premium fruit has a quality bar; you would rather sort out 3% now than explain a compromised 100% later.
Hold Block B.
- Loose bunches and thicker skins shed water and dry out, so rot pressure is materially lower.
- Seeds are green and the tannin is harsh - B is not physiologically ripe, and rain-induced sugar dilution will actually buy it hang time rather than cost it. pH 3.52 and TA 6.8 give it a buffer A does not have.
While A comes in, watch in B: berry splitting and any bunch closure, pH drift (sample daily, potassium moves fast), dilution of Brix, and the seed colour - the moment seeds brown and the tannin softens, B is ready. Plan to pick B 5–7 days after the weather clears.
2. Block A lands on the crush pad. Given 24.6 °Brix, pH 3.86 and TA 4.9 g/L, what do you do to the must, in what order, and what do you refuse to do?
Read the worked answer
The pH is the target, not the Brix. 24.6 °Brix is manageable; 3.86 with rain coming is not.
Order of operations
- Sort first, ruthlessly. Whole-bunch sorting for botrytis before the crusher. Botrytis brings laccase, which oxidises phenolic compounds and survives normal SO2 doses; a small percentage of clean fruit is worth more than a tonne of compromised fruit.
- Settle the microbiology. A modest SO2 addition at crush (in the region of 30–40 mg/L, adjusted for must pH) to slow oxidation and wild flora. Note that much of it will bind to botrytis-derived compounds and be less effective than the number suggests.
- Acidulate by bench trial, not by formula. Tartaric is the tool. Its effect on pH is non-linear and depends on the must's buffering capacity, so make up three trials at roughly 1, 1.5 and 2 g/L and measure pH on each. Pick the smallest addition that gets you to your target, because tartaric will partly precipitate as potassium bitartrate later and the pH will drift back up.
- Consider water addition only if the style target is below 24.6 °Brix, and only within your jurisdiction's permitted limit - check the rule before the tank is full, not after.
- Shorten skin contact and press earlier than usual for the style. Higher pH plus warm fruit plus botrytis is a recipe for a fast, sloppy extraction.
Refuse to: deacidify (you do not have an acidity problem), add acid to the whole lot without a bench trial, or blend in a high-acid lot at crush before you know what the ferment will do. Hold that decision until you can taste finished wine.
3. Suppose the rain were eight days out instead of three. What changes in your plan, and what does that tell you about how you were really deciding?
Read the worked answer
What changes
- You get to buy ripeness in A. With eight days you would sample A daily and pick perhaps 3–4 days before the front rather than immediately - capturing the flavour development that 24.6 °Brix and brown seeds suggest is close - while still leaving a buffer for crew and crush-pad scheduling.
- You would thin now. Dropping the botrytis-affected clusters in A this week removes the inoculum before the rain rather than sorting it out afterwards. Same cost, better timing.
- You would pre-position capacity. Book a second crew or extend shifts; eight days is enough warning to line up tanks so A and B are not competing for the same 20-tonne crush pad.
- B's decision stays the same, but for a firmer reason. Eight days of dry, warm weather would likely brown those seeds and soften the tannin. You would sample B on day 4–5 and be ready to pick it before the front if it turns, rather than after.
What it tells you about the decision The three-day version was not really a ripeness decision. It was a risk-allocation decision driven by two numbers - pH 3.86 and 3% botrytis - that made A's downside larger than its upside. The grape variety and the contract set the frame; the lab numbers set the clock. That is the reasoning to be able to state out loud, because the same two blocks with a pH of 3.60 and clean fruit would be picked in the opposite order.