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Rhubarb
Rhubarb arrives in May when nothing else has, which has earned it a permanent place in Baltic and Nordic kitchens. It is very acid, very low in pectin, and it freezes raw without blanching — three facts that between them explain almost every rhubarb recipe you will meet.
The season
The first crop of the northern year: pulled from May into June, and traditionally stopped around midsummer so the crown can rebuild for next season.
Acidity decides the method
Rhubarb stalks are strongly acid at roughly pH 3.1–3.4, which makes them one of the safest things to bottle.
This is a reference guide, not a recipe authority and not medical advice. The one organism the safety rules here are written against is Clostridium botulinum, and the one way to be protected against it is a tested recipe followed exactly — substitutions of the acid, the sugar or the salt are not cosmetic. Where the national food authority publishes advice for a specific food (Baltic fish, wild mushrooms), that advice outranks this page.
Method by method
| Method | Verdict | The note |
|---|---|---|
| Freezing | Best | Wash, chop into pieces, freeze raw on a tray. No blanching, no sugar, no fuss. |
| Drying | OK | Dries into tart chips; the high water content makes it slow work. |
| Fermenting | OK | Rhubarb ferments into a sharp soda or wine; not a staple preserve. |
| Pickling in vinegar | Good | Pickled rhubarb with ginger is a genuinely good preserve and very easy. |
| Jam and sugar preserves | Good | Low in pectin: pair with apple, redcurrant or gooseberry, or use a pectin sugar. |
| Water-bath canning | Best | Compote and juice process safely with no added acid at all. |
| Pressure canning | No | Unnecessary for a fruit this acid. |
| Curing and salting | No | No tradition. |
| Smoking | No | No tradition. |
| Root cellaring | Poor | Stalks hold a week or two in the fridge and no longer. |
The classic preparation: Frozen raw, and rhubarb compote
Freezing is the whole answer for a rhubarb glut and it takes ten minutes: wash the stalks, trim the ends, cut into two-centimetre pieces, spread on a tray, freeze until hard and bag. Rhubarb does not need blanching, because the texture is going to collapse in cooking anyway and there is no enzyme problem worth the trouble. For compote, simmer the chopped stalks with sugar to taste until they break down — rhubarb needs no water, it is nearly all water already — and either refrigerate it or fill hot jars and process in a boiling-water canner. No acid needs adding: rhubarb is one of the most acid things in the garden.
Preparation that matters
Pull the stalks rather than cutting them: a twist and a pull takes the whole stalk cleanly out of the crown, while a cut stub rots back into the plant. Cut the leaves off in the garden and leave them there. Rhubarb leaves contain enough oxalic acid to be genuinely toxic and are not food, not compostable into a salad, and not to be boiled into anything. The stalks themselves also contain oxalate, in ordinary and unremarkable amounts. Stop harvesting around midsummer so the plant can build reserves for next spring.
What the preserve is worth
Rhubarb by itself is barely 21 kcal per 100 g, and the calorie content of anything you actually eat is almost entirely the sugar you added. That is worth saying plainly, because rhubarb has a reputation as a light dessert fruit and a rhubarb crumble is not a light dessert. It contributes some vitamin K and fibre. Its oxalate content is relevant to a small number of people, mostly those with a history of calcium-oxalate kidney stones, and that is a question for their own clinician rather than a general warning.
The ways this goes wrong
- Doing anything at all with the leaves. They are toxic; they go on the compost heap, not in the pan.
- Cutting stalks instead of pulling them, which rots the crown.
- Expecting rhubarb jam to set on its own — it will not, without a pectin partner.
- Harvesting hard into late summer and weakening the plant.
Safety rules, temperatures, blanching times, headspace and the pH 4.6 line: USDA Complete Guide to Home Canning and the National Center for Home Food Preservation guidance (US Government / land-grant publications, public domain). Acidity classes: the FDA's published approximate-pH tables. Jam composition: Directive 2001/113/EC. Fish freezing before raw or lightly cured use: Regulation (EC) No 853/2004, Annex III. Checked 2026-09-06.
Sources for this food
Frequently asked questions
Are rhubarb leaves poisonous?
Yes. The leaf blades contain enough oxalic acid and related compounds to be toxic, and they should never be eaten, juiced or cooked. Cut them off at harvest and compost them. The stalks are perfectly safe.
Does rhubarb need blanching before freezing?
No. Chop and freeze raw. It will be soft when it thaws, which is exactly what a compote or a crumble wants anyway.
Why will my rhubarb jam not set?
Rhubarb is very low in pectin. Add a cooking apple, redcurrants or gooseberries to the pan, or use a jam sugar with pectin in it.
Related pages
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Nutrition figures
The published USDA row for this food, per 100 grams.
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