Fermentation Time Calculator

How the calculator works

Pick what you are fermenting and enter the temperature of the room it will sit in, or for kimchi, whether it will sit out or go in the fridge. The calculator finds the published time for that range. If you add a start date, it turns the time into dates: when to start checking and when it should be done.

The calculator does not stretch the published times to fit other temperatures. The National Center for Home Food Preservation (NCHFP) gives sauerkraut times for 70 to 75 °F and for 60 to 65 °F, but nothing for 66 to 69 °F. If your room is 67 °F, you get the closest published range and a note, not a made-up figure.

Temperatures are rounded to the nearest degree, so 75.4 °F counts as 75 °F. Celsius is converted to Fahrenheit first.

The published times

Food	Where or how warm	Time
Kimchi	Room temperature, about 68 °F	1 to 2 days
Kimchi	Refrigerator	3 to 4 days
Sauerkraut	70 to 75 °F	3 to 4 weeks
Sauerkraut	60 to 65 °F	5 to 6 weeks
Dill pickles	70 to 75 °F	3 to 4 weeks
Dill pickles	55 to 65 °F	5 to 6 weeks
Kombucha	68 to 77 °F	7 to 10 days

NCHFP’s general guidance says regular dill pickles and sauerkraut ferment and cure for about 3 weeks, and refrigerator dills for about 1 week. The warmer range is the one it calls the best for the bacteria that do the fermenting: 70 to 75 °F for cucumbers.

Worked example

You pack a crock of sauerkraut on 9 November in a kitchen that stays at about 72 °F.

1. 72 °F falls in the 70 to 75 °F range.
2. NCHFP gives about 3 to 4 weeks at that range.
3. 9 November plus 21 days is 30 November, so start checking then.
4. 9 November plus 28 days is 7 December, the latest it should take.
5. The real signal is the bubbling: NCHFP says the kraut is fully fermented when it stops.

If the kitchen cools to 64 °F in winter, the same crock moves to the 60 to 65 °F range and 5 to 6 weeks.

Kimchi is different

Kimchi ferments in days, not weeks, and the guide used here times it by where it sits rather than by an exact temperature. Colorado State University Extension gives 1 to 2 days in a well-ventilated room at about 68 °F, or 3 to 4 days in the refrigerator, which it suggests in hot weather.

The calendar is only a guide. The extension says to test the kimchi daily with pH strips and to make sure it reaches pH 4.6 or below, with 4.2 as the best. Once it is ready, keep it refrigerated, tightly covered and pressed down, and eat it within about 2 weeks for the best quality.

Signs of trouble

• Scum on top. Wild yeasts and bacteria form a scum on the brine. NCHFP says to remove it as often as needed, because it feeds on the acid.
• Soft or slimy pickles. A sign the brine was too weak or the room too warm. If pickles are soft, slimy or smell disagreeable, NCHFP says to discard them.
• Pickles above the brine. Keep cabbage and cucumbers 1 to 2 inches under the brine the whole time.
• Shriveled pickles. NCHFP lists a brine that was too strong as one cause.

Kombucha safety

The NCHFP kombucha recipe has two rules worth knowing. The starter liquid must be pH 4.0 or lower before you begin; above that, NCHFP says not to make kombucha with it. And once it has fermented, refrigerate it straight away and use it within 30 days. Do not leave finished kombucha sealed at room temperature: NCHFP warns that the gas can build up until the container bursts.

After fermenting

• Kimchi: refrigerated, eat within about 2 weeks for the best quality.
• Sauerkraut: tightly covered in the refrigerator for several months, or canned.
• Dill pickles: refrigerated in the original container for about 4 to 6 months, removing scum regularly. NCHFP says canning is the better way to keep them.
• Kombucha: refrigerated, within 30 days; within 2 days once flavorings are added.

Tips and common mistakes

Measure the room, not the thermostat. A crock by a window or a warm appliance can sit several degrees off the room setting.

Start the clock on the day you pack it. The times above run from packing to finished.

Taste and test rather than trusting the date. Temperature swings change the pace, which is why every guide here also gives a sign to watch for.