Making Blackberry Jam with Foraged Fruit

By A Forager's Guide to Safe Mushroom Picking
Comments 35
17 Jul 2026

Making Blackberry Jam with Foraged Fruit

Picking a Hedgerow Harvest

British blackberries are at their best from late August through to the first sharp frosts of October, and a good hedgerow can fill a tub in under an hour. Look for berries that are jet black all over and pull away from the core with almost no resistance — those are fully ripe and sweet. Anything still showing red or purple is underripe, sour, and will drag your jam's flavour down. A few firm, slightly Underripe berries are worth including, though, because they carry more pectin and help the set.

Pick after two or three dry days if you can. Rain-sodden berries are watery, prone to mould, and will give you a loose, insipid jam. Wear long sleeves and gloves, or carry a walking stick to hook high canes towards you. Brambles are unforgiving, and the best fruit is always just out of reach. Avoid busy roadside verges where exhaust fumes settle on the fruit, and steer clear of fields that may have been sprayed. On popular footpaths, pick above dog height. Foraging fruit for personal use is a long-standing right in the UK, but always ask permission on private land and never strip a bush bare — leave plenty for the birds and for next year's crop.

Equipment and Ingredients

Blackberry jam is one of the simplest preserves you can make, but the right kit makes the difference between a good set and a runny disappointment.

A large, wide preserving pan or heavy-based stockpot — jam boils up dramatically, so leave plenty of headroom
A long-handled wooden spoon or heatproof spatula
A jam thermometer (helpful, but not essential)
A fine nylon sieve or a square of muslin for seedless jam
Clean jars with lids, plus a wide-necked funnel and a ladle
For every 1kg of prepared fruit: 750g–1kg granulated or jam sugar, and the juice of one lemon

Work in batches of no more than 2kg of fruit at a time. Larger quantities take too long to reach a set and the flavour dulls.

Preparing for a Smooth Set

Tip your haul into a sink of cold water and swish gently, then lift the berries out rather than draining the water over them — grit sinks. Discard any that are mouldy, squashed or carrying small white maggots (the larvae of the raspberry beetle, harmless but unwelcome). Spread the fruit on a tray and pick out leaves and stalks.

For a truly smooth jam, cook the fruit first with a splash of water and the lemon juice until it collapses, then push it through a fine sieve or a muslin-lined colander to remove the pips. It is fiddly work, but the result is a glossy, seedless preserve that spreads like silk. If you prefer a more rustic, hedgerow character, simply mash the fruit roughly with a potato masher and leave the pips in — they are entirely edible.

Balancing Fruit, Sugar and Lemon

Blackberries sit low-to-moderate on the pectin scale, which is why so many home-made batches end up syrupy. Two things fix that: acid and sugar discipline. The lemon juice is not there for flavour alone — pectin needs acid to gel, and blackberries can be short of it. One lemon per kilogram of fruit is a good rule; add a little more if your berries taste flat.

Sugar is the other lever. Personally, I use 750g of sugar per kilogram of prepared fruit for a soft-set jam with real fruit flavour, and up to 1kg if I want a firmer, longer-keeping preserve. Warm the sugar in a low oven before adding it — it dissolves faster, which means less time cooking and a fresher taste. Stir the sugar into the fruit off the heat until every grain has gone; gritty jam is nearly always sugar added to a boiling pan.

Cooking and Testing for a Set

Bring the pan to a full rolling boil — one that cannot be stirred down — and hold it there for 5–10 minutes, stirring often to stop it catching. Skim off the pinkish foam as it rises; it clouds the finished jam.

Start testing after five minutes. Put a saucer in the freezer before you begin, then drop a teaspoon of jam onto the cold plate, leave it a moment, and push it with your fingertip. If the surface wrinkles and the jam holds its shape, it is ready. A jam thermometer should read 104–105°C. If it is still liquid, boil for two more minutes and test again. Over-boiling darkens the colour and sets the jam hard, so trust the wrinkle test over the clock.

Potting, Sealing and Storing

Sterilise your jars by washing them and drying them in an oven at 140°C for 20 minutes, or by running them through a hot dishwasher cycle. Fill them while both jam and jars are hot, right to the brim, and screw the lids on firmly. As the jam cools it contracts and pulls the lid down tight, giving you a reassuring vacuum seal.

Label with the date and store somewhere cool and dark. Unopened, your jam will keep for a year or more; the colour fades after about nine months, though the flavour holds. Once opened, keep it in the fridge and use it within a month. A spoonful on hot toast, swirled through yoghurt, or loosened with a little water and spooned over vanilla ice cream is the hedgerow's reward for a scratched forearm or two.

Preserves

Cooking with Wild Plums and Damsons

Identify lemony sorrel, wild rocket and chickweed to add fresh flavour to salads, soups and sauces from spring through autumn.

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5 Comments

Robert Sonny says Jul 21, 2024 at 10:00am

I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
Reply
- John Abraham says Jul 21, 2024 at 10:00am
  
  I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
  Reply
  - Robert Sonnysays Jul 21, 2024 at 10:00am
    
    I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
    Reply
Robert Sonny says Jul 21, 2024 at 10:00am

I must explain to you how all this mistaken idea of denouncing pleasure and praising pain was born and I will give you a complete account of the system
Reply

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