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Is this mold?

Three questions. One answer: eat, fix or bin.

Illustration: a jar of sauerkraut surrounded by cabbage, garlic, dill and peppercorns
Check my jar Rules from USDA & FDA guidance · sources
Question 1 of 3

Anything fuzzy, raised or coloured on top?

Look from the side, in daylight.

Open it. Does it smell sour?

Tangy, sharp, a little sulphur from cabbage. All normal.

Is everything under the brine?

Mold can only start where air touches food.

Eat

That's fermentation.

A flat white film is kahm yeast. Skim it off. Cloudy brine and bubbles are normal. Taste it; fridge when it's sour enough for you.

Acid is what keeps it safe: at pH 4.6 or below, botulism bacteria can't grow.1

Keep this answer on your fridge.

Printable "Is this safe?" page + salt chart, then 4 short emails. Unsubscribe anytime. Privacy
Fix

Push it under. Check tomorrow.

Press everything below the brine with a clean spoon. Low on liquid? Top up with brine: about 25 g salt per litre of water.2 Weigh it down with a leaf or a small bag of brine.

Mold needs air. The brine keeps air out.

Never guess the salt again.

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Bin

That's mold. Bin the whole jar.

In soft, wet food, mold spreads below what you can see. Don't scoop around it. Wash the jar hot. Next time, keep everything under the brine.

USDA advice for moldy soft foods: discard.3

Make the next jar work.

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Bin

Wrong microbes won. Bin it.

Sour is the only right smell. Rotten or putrid means spoilage got ahead, usually too little salt or too warm a room. Next jar: weigh the salt, find a cooler spot.

When in doubt, throw it out.3

Get the salt right next time.

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Keys 1 / 2 to answer · Esc to start over

Scrub through two weeks

What normal looks like.

Day
0

Packed

Pressed under its own brine. Lid loose.

An illustration rendered from two reference frames, not a recording of one jar. Around 20 °C. Cooler kitchens run slower.2

Inside the book

Four jars. Four weeks.

Pages from the book, as they print. Drawings, not stock photos. Tap a page to read it.
Who wrote this

I'm Michael, and I write from a kitchen in Poland. I binned my first jars because nobody would just say: flat is fine, fuzzy isn't. This is the book I wanted at jar one.

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Cover of Fermentation Without Fear
The book

Fermentation Without Fear

Four jars, four weeks, twenty recipes. One PDF for print (A5) and one for your phone.

  • "Is this safe?" poster: eat, fix or bin at a glance
  • One jar a week: what you'll see, what to do, day by day
  • 20 one-page recipes, all weighed in grams
  • Every safety rule with its source · 76 pages · free updates by email
Get the book for $9 $12 after launch 14-day refund, no questions. Secure checkout by Lemon Squeezy.
I've never fermented. Is this for me?

Yes. Week one is cabbage and salt, the most forgiving jar there is.

What if my jar still goes wrong?

Every page says what to do next: eat, fix or bin. If the book doesn't help, reply to your receipt for a refund.

Is this medical or health advice?

No. It's food-safety practice from USDA and FDA guidance, with sources. No health claims.

Sources
  1. US FDA, 21 CFR 114.3: acidified foods, equilibrium pH 4.6 or below. eCFR
  2. National Center for Home Food Preservation (USDA-funded): sauerkraut, salt ratio, keeping food submerged, fermenting temperatures. nchfp.uga.edu
  3. USDA FSIS: Molds on food, are they dangerous? fsis.usda.gov