Want to make perfect homemade kimchi or sauerkraut? Temperature is one of your main allies! No need for sophisticated equipment: between your kitchen, fridge, or cellar, you already have all the fermentation space you need.
This article clearly explains how temperature affects fermentation and guides you in placing your jars in the right place to obtain crunchy, tasty vegetables packed with probiotics.
Psst, are you looking to find out about the best temperature for other fermentations? See our guide Best Temperature for Fermentation?
Temperature and Lacto-Fermentation: What You Need to Know
Lacto-fermentation works very well at room temperature, but each stage has its ideal temperature range:
Starting fermentation (59° to 77°F)
Lacto-fermentation is easy to do at room temperature, between 59° and 77°F (15° and 25°C). However, for optimal quality of fermented vegetables, such as sauerkraut or kimchi, it is best to maintain the temperature between 59° and 68°F. Research indicates that the ideal temperature is around 64°F, as this allows for optimal growth of lactic acid bacteria and offers a perfect balance between flavour, crunchy texture and food safety (ref.).
Avoid:
- Temperatures above 77°F: fermentation is too rapid, resulting in high acidity and softened vegetables.
- Temperatures below 59°F: fermentation is too slow and there is an increased risk of mold growth.
Tip: Take advantage of the moderate autumn temperatures to start your lacto-fermentation in the best conditions.
Storing your jars (39°F, in the fridge)
Store your lacto-fermented products at a temperature of around 39°F (4°C) — the standard fridge temperature. At this temperature, fermentation slows down significantly, preserving flavours, crunchy texture, and probiotics for several months. So, if you’ve ever wondered how long kimchi can last in the fridge, it’s longer than you will need before you finish the jar!
Where to Store Your Fermentation Jars?
Here are the best places to store your homemade fermentations:
Kitchen (64 to 77°F)
- Ideal for starting fermentation: Bacteria act quickly, developing flavours and acidity in about a week. You can allow fermentation to continue longer, depending on your tastes and preferences.
- 🚨 Caution: Avoid areas near sunny windows, ovens, or radiators, which are sources of significant temperature variations.
Fridge (39°F)
- Perfect for storage: The cold greatly slows down fermentation, preserving quality over a long period of time.
- When: Place in the refrigerator after 1 to 4 weeks at room temperature, depending on the desired acidity.
Cellar, Basement or Garage (50-59°F)
- Alternative to the fridge: slower maturation, ideal for developing deep flavours.
- 🚨 Caution: Make sure the area is ventilated, clean, and not too humid to prevent mold growth.
What if You Don’t Have Enough Space in Your Fridge?
If your fridge is full, not to worry! Unopened jars can be left at room temperature for several months or even years. However, keep in mind that fermentation will continue slowly, gradually increasing acidity and subtly altering the flavour and texture of the vegetables. Some recipes, such as fermented garlic, hot sauces or fermented lemons, even benefit from ageing for a long time at room temperature without becoming overly acidic.
What to Do if the Temperature Varies?
Seasonal variations are normal. Here’s how to adapt:
- Too hot (above 77°F): shorten the fermentation time (3 to 5 days), then transfer to the fridge.
- Too cold (below 50°F): place the jars in a warmer area to activate the bacteria, or, if this is not possible, extend the fermentation time. Alternatively, add an external source of bacteria, such as brine from a previous lacto-fermentation or Caldwell Starter Culture, to help start the fermentation process.
Temperature and Safety: The Role of Acidity
Acidity, measured by pH, is essential for ensuring food safety. A pH of 4.3 or lower effectively inhibits pathogenic bacteria, particularly Clostridium botulinum, which causes botulism (ref.).
For example, in kimchi, acidity changes relatively quickly depending on the temperature:
- At 77°F: safe pH (<4.3) reached in 5 days
- At 59°F: safe pH reached in 12 days
- At 46°F: safe pH reached in about 30 days
Thus, a high temperature allows a safe level to be reached quickly but can negatively affect texture and taste. A moderate temperature, around 64°F, remains ideal for a perfect balance between safety, taste, and texture.
Evolution of kimchi pH during fermentation (ref.)
Get the Tools!
We suggest the following products for making lacto-fermentations.
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