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Canned Rhubarb
Wash the rhubarb thoroughly in pure water; cut it into pieces and pack it in sterilized jars. Cover with cold water; let it stand ten minutes; pour off the water; fill again to overflowing with fresh cold water; seal with sterilized rubber rings and covers, and set away in a cool, dark place.
This is the old "cold water" method of putting up rhubarb, which relies on the plant's acidity alone and applies no heat at all. It does not meet any current standard for home canning, and the specific failures are worth understanding.
- There is no processing stepNothing in this method ever heats the jar or its contents. Packing raw stalks in cold water and screwing down a lid is storage, not canning, and nothing in the procedure kills the yeasts, moulds and bacteria that arrive on the rhubarb from the field.
- The jar never actually sealsThe jar has no vacuum seal -- A vacuum seal is formed when hot contents cool and contract. A cold-packed jar has no vacuum, so the closure depends entirely on mechanical pressure on the rubber ring. Gas from fermenting contents can push past such a seal, and air can move the other way.
- Sterile jars, unsterile foodThe recipe is careful about sterilising the glass, the rings and the covers, which reflects the period's understanding of preserving. But the rhubarb itself is never treated, so the sterile container is filled with a live culture.
- Acidity protects less than it seemsRhubarb is genuinely acidic, around pH 3.1 to 3.4, which is why this method appeared to work and why Clostridium botulinum is not the first concern. Moulds and film yeasts grow happily at that pH, and as they consume the acid they raise it — a spoiled jar can become hospitable to organisms that the fresh pack excluded.
- Rubber rings and bail-top jarsRubber rings and covers -- The "sterilized rubber rings and covers" indicate a jar closed against a rubber gasket, whether a screw cap or a wire bail; both were in ordinary use. Those gaskets perished with age and heat and were renewed regularly. Old jars of this kind should not be relied on for preserving today.
- The leaves, alwaysOnly the stalks are food. Rhubarb leaves contain oxalic acid and other compounds at levels that cause poisoning, and they must never go into the jar, the compost pot for stock, or anything else destined to be eaten.
- What to do insteadRhubarb keeps extremely well frozen, raw and cut, with no treatment beyond a bag. If you want it in jars, follow a current tested recipe from a food-safety authority for the processing time and method.
Cold-water canning of rhubarb appears in North American and British household manuals of the nineteenth and early twentieth centuries, and it persisted in print in part because it so often seemed to succeed — the exclusion of air kept many jars drinkably sound through a winter, and the failures were written off as bad luck with a jar. Rhubarb earned its place in books like Mrs Fryer's for a simple calendar reason: it is the first thing the northern kitchen garden produces, arriving weeks before any true fruit, and so much of it was put by. Its old name, pie plant, comes from its use in pies. The change in advice came with the extension services and the wartime canning bulletins of the early twentieth century, which pushed households toward measured heat processing and away from methods that relied on the character of the food alone.