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Blackberries
To every pound of blackberries allow a quarter of a pound of sugar. Put the berries in a porcelain-lined kettle, sprinkle over the sugar, stand aside one or two hours. Then put over a moderate fire, bring to boiling point, skim and can immediately.
This is open-kettle canning: hot fruit is poured into jars and sealed with no processing afterwards. That method was standard in home kitchens well into the twentieth century and is no longer considered sound, so the notes below explain the failure rather than offering a revised procedure.
- No processing step at allThe instruction is to bring the fruit just to a boil and "can immediately." Nothing sterilises the jar contents or the headspace after filling, and nothing is specified about lids, jar preparation, or a boiling-water bath. Any current tested recipe for blackberries specifies a measured water-bath time by jar size and altitude.
- Seals that look right and are notOpen-kettle jars often form a vacuum as they cool, which reads as success. The seal can be weak or the food already contaminated from the transfer, and spoilage may not be visible before the jar is opened months later.
- Mould and yeast, not botulismBlackberries are high-acid fruit, so Clostridium botulinum is not the concern here; the realistic risks are yeasts, moulds and heat-resistant fungi that survive an unprocessed pack. Some moulds growing on stored fruit produce mycotoxins, which is why unprocessed sweet packs are discarded rather than skimmed and eaten.
- The sugar is not a preservative at this levelA quarter pound of sugar to a pound of fruit is roughly one part sugar to four parts fruit by weight. That is a light sweetening for flavour and colour, far below the concentration in a jam or a syrup-preserved fruit that would inhibit microbial growth on its own.
- What the maceration step was forStanding the sugared berries one or two hours draws juice out by osmosis so the fruit cooks in its own liquid and holds its shape. That part of the technique is sound and still used in fresh compotes and quick jams; it is the sealing that is the problem.
- Porcelain-lined kettleThe specification matters because bare cast iron and unlined copper react with fruit acid, dulling the colour and adding a metallic taste. A modern stainless-steel or enamelled pan does the same job.
- If you want blackberries put byUse a current tested water-bath recipe from a reliable preserving guide, or freeze the sugared fruit, which needs no processing schedule at all.
Open-kettle canning of soft summer fruit is what many nineteenth-century American cookbooks appear to have meant by "canning": fill, seal, hope. It survived because high-acid fruits are relatively forgiving and because glass jars with reusable rubber rings and screw or clamp closures made a passable seal without a processing bath. Blackberries were thorny, perishable and abundant in hedgerows and cut-over woodland, so they arrived in the kitchen in quantity and all at once. Proportions given per pound rather than per jar are the ordinary idiom of the period for fruit of every kind.