Harvesting, ripening, and saving seed

Harvest when fruit is fully coloured and gives slightly to gentle pressure. Heirlooms often ripen unevenly — Brandywine may stay green-shouldered even when the rest is pink; this is normal. Smell the stem end: ripe tomatoes smell sweet and faintly sharp. Pick by twisting gently or cutting the stem with secateurs. Paste tomatoes like San Marzano are ready when deep red and firm — they will soften off the plant if you pick early.

In late September, before the first frost, pick all remaining fruit. Green tomatoes ripen indoors if brought inside before cold damages them. Place them in a cardboard box with a ripe banana (which releases ethylene) and check every few days. They will ripen over 2–4 weeks. Flavour is not as good as vine-ripened fruit, but far better than supermarket tomatoes.

Save seed from heirlooms by choosing the best fruit from the healthiest plant. Scoop seeds and pulp into a jar, add a little water, cover loosely, and leave at room temperature for 3–5 days until a mould layer forms on the surface. This fermentation kills seed-borne diseases. Pour off the mould, rinse seeds in a sieve, spread on a plate, and dry for a week. Store in a paper envelope labelled with cultivar and year. Seed stays viable for 4–6 years.