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Fermented Vegetables & Fruit

Fermented Swiss Chard: Stems and Leaves in a 3% Brine, and When It’s Safe to Eat

By Updated 2 min read

At a glance

Swiss chard stems and leaves ferment well in a weighed 3% salt brine, kept submerged at room temperature for about 5–10 days. Chard is high in nitrate, which turns partly into nitrite early in fermentation; nitrite then falls as the brine becomes sour. Eat fermented chard only when it's evenly sour, rinse it, keep it in the fridge, and don't give it to babies.

  • Use a weighed 3% brine (30 g salt per litre) and keep chard submerged.
  • Leaves sour in about 5–7 days at 18–22°C; stems take 7–10 and stay crisp.
  • Chard had more nitrate than spinach or cabbage in market samples.
  • Nitrite peaks early in fermentation and falls once the brine is properly sour.
  • Eat it only when evenly sour, rinse it, and don't give it to babies.

Ferment profile

Origin
Home fermentation (leafy-green brine pickle)
Fermentation
Lactic acid
Main microbes
Lactic acid bacteria from the leaves
Live cultures
Yes
Alcohol
None / trace

Swiss chard ferments well: the thick, colourful stems stay crunchy like a pickle, and the leaves turn soft and tangy, like a milder version of fermented mustard greens. The method is the same as for other leafy-green ferments – salt brine, everything kept under, a week or so at room temperature – with one point that matters more for chard than for cabbage: nitrate.

Chard, Nitrate and Nitrite

Leafy greens store nitrate from the soil, and chard stores a lot: in market samples of Swiss chard, spinach and white cabbage, chard had the highest nitrate levels of the three. The same study notes that nitrate and nitrite matter most for young children, in whom they can cause methaemoglobinaemia, a condition that reduces the blood’s ability to carry oxygen (Luetic et al., 2025). Much of the concern is about its conversion to nitrite. When pureed leafy greens were left at room temperature, nitrite rose as nitrate fell – in arugula, to about 2,450 mg/kg after 48 hours (Clayton-Cuch et al., 2025).

Fermentation goes through the same conversion at the start and then clears it. In fermenting cabbage, nitrite peaks in the first days, while the brine is still only mildly acidic, and falls to almost nothing once the lactic acid bacteria have made it properly sour (Xu et al., 2024; Pu et al., 2001). So the rule for fermented chard is the same as for dưa muối and gundruk: eat it only when it’s evenly and clearly sour, not half-done, rinse it before serving, and don’t give it to babies.

Salt and Timing

Use a weighed brine of 3% (30 g salt per litre of water) and keep everything submerged. The stems take longer than the leaves and stay crisp, so cut them separately into sticks. At 18–22°C the leaves are usually evenly sour in 5–7 days and the stems in 7–10. A well-soured brine is well below pH 4.6, the line US regulations use for acidified foods (21 CFR 114); refrigerate it once it gets there to stop it going soft. For films, soft pickles and off smells, see the NCHFP’s guide to problems with fermented pickles and our troubleshooting guide. For other leafy greens, see fermented kale.

Using It

Chop the leaves into grain bowls, eggs or beans, or stir them into soup at the end of cooking; slice the stems as a pickle. Chard also works mixed into sauerkraut – about one part chard to three parts cabbage.

Recipe: Fermented Swiss Chard (3% Brine)

Makes
One 1-litre jar
Hands-on
20 min
Fermentation
5–10 days at 18–22°C
Salt
3% of the water's weight (30 g per litre)
Temperature
18–22°C (64–72°F)
Difficulty
Easy

Equipment

  • Kitchen scale
  • 1-litre jar with an airlock lid or loose lid
  • Fermentation weight

Ingredients

  • About 500 g Swiss chard (fresh and firm; no yellow or slimy leaves)
  • 600 ml water (unchlorinated or boiled and cooled)
  • 18 g salt (non-iodized; 3% of the water)
  • Optional 2 garlic cloves, a few slices of fresh chilli

Method

  1. Wash the chard well. Cut the stems into 8–10 cm sticks and the leaves into wide ribbons.
  2. Dissolve the salt in the water.
  3. Pack the stems upright into the jar, push the leaves in on top with any garlic and chilli, and pour over the brine. Weigh everything down so it stays at least 2 cm under.
  4. Close with an airlock lid (or a loose lid, burped daily) and keep at 18–22°C, out of direct sun.
  5. Taste from day 5. It's ready when the leaves are olive-green and evenly sour and the stems taste sour right through – usually 5–10 days. Don't eat it while it's still mild and half-done.
  6. Refrigerate and eat within about 4 weeks. Rinse it before serving.
  7. Discard the batch if it grows fuzzy mould, turns slimy or smells rotten.

Frequently asked questions

Can you ferment Swiss chard?

Yes. Stems and leaves ferment well in a 3% salt brine in about 5–10 days.

Do I ferment the stems or the leaves?

Both. Cut the stems into sticks – they stay crisp – and the leaves into ribbons; the leaves sour faster.

Is fermented chard high in nitrite?

Nitrite rises in the first days of fermentation and falls once the brine is properly sour, so eat it only when it's evenly sour.

Can babies eat fermented chard?

No. High-nitrate greens and their ferments aren't suitable for babies, who are most sensitive to nitrate and nitrite.

How long does fermented chard keep?

About 4 weeks in the fridge, kept under its brine.

Sources

  1. Luetic S et al. (2025). Nitrates and nitrites in leafy vegetables: the influence of culinary processing on concentration levels and possible impact on health. Int J Mol Sci 26(7):3018. Link
  2. Clayton-Cuch D et al. (2025). Nitrite, nitrate and N-nitrosamine occurrence in processed nitrate accumulating vegetables stored under different conditions. Food Chem 493(Pt 1):145631. Link
  3. Xu X et al. (2024). Analysis of microbial diversity dominating nitrite enzymatic degradation and acidic degradation in the fermentation broth of Northeast sauerkraut. Foods 13(24):4168. Link
  4. Pu C et al. (2001). Research on the dynamic variation and elimination of nitrite content in sauerkraut during pickling. Wei Sheng Yan Jiu 30(6):352–354. Link
  5. eCFR. 21 CFR Part 114 – Acidified foods. Link
  6. National Center for Home Food Preservation. Causes and possible solutions for problems with fermented pickles. Link
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