Peppers at thirty-four degrees: an August of jars on the balcony

i. The balcony in August

The thermometer clipped under the balcony rail read thirty-four degrees at five in the afternoon on most days last August and did not drop below twenty-six at night. The street is narrow enough that the building opposite throws a little shade after six, and the tiles hold the heat long after that. Inside the flat, the kitchen cupboard under the counter on the north wall ran about four degrees cooler than the balcony, which is the single most useful fact I discovered all summer.

I started six jars of peppers on the first Saturday of the month from one stall that had a crate of long green frying peppers and a smaller tray of red ones. Three jars went outside and three into the cupboard, with identical brine made from the same jug so that the only difference between them was where they stood. It is the closest thing to a controlled comparison I have ever managed in a flat this size.

Each jar held about four hundred grams of peppers, pricked twice near the stem, with a clove of garlic, a bay leaf and a few peppercorns, and was topped up with brine to within two centimetres of the rim. A small glass weight held everything down. I wrote the jar number, the place and the balcony reading on the tape of each one, and I checked all six at half past seven every morning before leaving for work, which in August is the only cool half-hour of the day.

ii. Brine strength and the white film

Every jar was four percent brine against the water, with the peppers pricked twice near the stem so the brine could get inside. Within two days all three balcony jars had a thin white film on the surface, the wrinkled, flat, slightly powdery layer that is almost always kahm yeast rather than mould. The cupboard jars took five days to show the same thing, and it was thinner when it came.

Kahm yeast is not dangerous, but it tastes of stale bread and cardboard if you let it settle in, and it tends to arrive alongside a softening of whatever is underneath. I skimmed the balcony jars every morning with a clean spoon, and on the fourth day I added a small extra weight so the peppers stayed well under. What I have learnt since is that the yeast mostly shows up where there is air, warmth and a gap between the vegetable and the surface, so a fuller jar with less headspace suffers less.

• White, flat, wrinkled and dull: kahm yeast, skim it off and keep watching
• Raised, fuzzy, blue, green or black spots: mould, and the jar goes
• Pink or orange tint in the brine: I do not argue with it and I bin the jar
• Brine cloudy and fizzy in the first week: normal, and a good sign

iii. The lid that did not hold

On the ninth day one of the balcony jars pushed its lid far enough off the seal that brine ran down the glass and into the drainage channel on the tiles. It was a clip-top jar with its rubber ring perished by two summers in the sun, and the gas built up faster than the tired ring could let it out gently. Nothing exploded, but the peppers at the top were left exposed to the air for the whole afternoon and were soft and grey by the evening.

The rest of that jar was fine once I dug down, but I threw it out anyway because I had no idea how long the air had been at it. Since then every clip-top jar gets a new ring at the start of each summer, and the balcony jars are loosely lidded screw-tops that I burp each morning. It is a small daily job, and it has become part of watering the geraniums before work.

iv. What came out at the end of the month

After three weeks I opened all five surviving jars on the same evening and tasted them side by side with a friend who cooks, who had not been told which was which. The cupboard jars were crisp all the way through, sour with a clean edge, and the red peppers had a sweetness that stayed. The two balcony jars were more sour, noticeably softer at the thin end, and one had the faint bready note the kahm leaves behind. She picked the cupboard jars every time without being prompted.

My summer rule now is simple and not very romantic. Peppers are started in the cupboard, and only moved out onto the balcony once they are sour enough to eat, when the brine can hold its own. The balcony is kept for cool-season jars and for drying chillies on a string, which it does perfectly. When a reader of the notebook writes to say their summer batches keep going soft, this entry is the one I point them to first.