Rainfall, and what a wet autumn does

Apple trees transpire heavily through the summer and set the size of their fruit in the weeks after June drop, when cell expansion is at its fastest. Reliable rainfall through that period gives full-sized fruit without irrigation, and it is the reason the maritime west of Britain, Normandy, Brittany, Asturias and the Basque country all became cider country while drier continental interiors did not.

Winter rainfall is a mixed blessing. It refills the soil profile, which is what carries an unirrigated orchard through the following summer, but it is also what makes drainage the first question at any site. A soil that stores winter rain in its pores and gives it back through the summer is ideal; a soil that holds it as standing water is not.

The cost of a wet climate is disease. Venturia inaequalis, the scab fungus, needs a period of leaf wetness at the right temperature to infect, and a wet spring supplies a series of them. Canker infection is likewise favoured by rain at leaf fall. This is the direct trade for the free water: cider regions do not irrigate, and cider regions have scab and canker as a permanent condition rather than an occasional event.

Rain in the weeks immediately before harvest dilutes the crop. Fruit takes up water, the specific gravity of the expressed juice falls, and a blend that would have fermented to a certain alcohol comes in below it. The effect is real but modest and temporary — a few days of drier weather will reverse part of it — and it is one reason experienced growers watch the forecast as closely as the starch test when deciding on a picking date.

Heavy rain on ripe fruit can also cause splitting in some cultivars, particularly after a dry spell, as the fruit takes up water faster than the skin can accommodate. Split fruit is an entry point for rot and it does not keep, which pushes it towards immediate milling rather than storage.

Season-long rainfall patterns show up more subtly, in the balance of the juice rather than only in its strength. A wet, cool season tends to produce fruit lower in sugar and often higher in acid than the same cultivar in a warm dry season, which is the ordinary vintage variation that makes single-year, single-variety cider a different drink from one year to the next.

Cider fruit is largely harvested off the ground, which makes autumn ground conditions a central operational constraint. A mechanical harvester sweeping fruit from a soft, wet sward picks up mud and grass with it, and the wetter it gets the more of both. Mud carries soil bacteria and mould spores into the mill, and grass fouls the machinery. On a badly wet site the harvester will also rut the alleys and compact them for years.

Fruit lying in wet grass deteriorates fast. A sound apple has an intact skin and considerable resistance to infection, but bruised or split fruit lying in constant moisture is colonised within days, and the organisms that arrive first — Penicillium expansum and the brown rot Monilinia species among them — are exactly the ones that matter for both quality and safety. In a dry autumn a grower can leave fruit on the ground for a week or two without much harm; in a wet one, that window closes to a matter of days.

The response is operational rather than chemical: mow the sward short before the fall so fruit can be found and gathered, gather more often in short passes rather than once in a long one, sort out the rotten fruit rather than pressing it, and mill promptly rather than storing wet fruit in deep heaps where it will heat.