5 Tips for Fermenting in Hot Weather

Dare I say it, but it looks like here in the UK we’re summer weather has reappeared. And fingers crossed, there are some warm days ahead of us. But was does summer weather mean for your ferments? And what might you need to do differently when fermenting in the summer?

Like us, the microbes love being warm. Warm, but not hot—to visualise this, think sitting in the shade in your back garden in with a nice breeze blowing, rather than baking on a black sand beach in Greece in the middle of August.

Optimal temperatures for fermenting range between 18-22°C/65-72°F, so if a ferment is too cold, it will still ferment, but just take longer. It if gets too warm it will speed up the rate at which the bacteria work, meaning your ferment will ferment quicker, which sounds good but isn’t necessarily the case. Or if say left in direct sunlight in a suntrap of a kitchen it could get too hot (above 42°C/107°F), the beneficial bacteria will die.

When a ferment ferments too quickly, it can mean that the different beneficial bacteria may not have enough time to do their jobs in terms of lowering the pH of the brine, creating the associated by-products and at the very basic, persevering the food. Generally, the bacterial fermentation process takes place in two stages, but more on that another time, and each stage needs to provide the bacteria with adequate time. Another downside of fermenting too quickly in warm weather is Kahm yeast. Kahm yeast crops up in a ferment when all the starches and sugars are used up by the bacteria fermenting at a faster pace. And this can also happen when the external temperature is warm and the pace of fermentation is sped up by the heat.  

So, if you have the pleasure of living somewhere warm or for as long as we have lovely summer weather, here is my advice for fermenting in warm weather:

  • Try to find a fermentation spot with the ideal temperature range. You can check the temperature with a thermometer, leaving it over a couple of days to get a consistent reading.
  • Always keep your ferments out of direct sunlight and avoid storing in places that retain lots of heat in warm weather. 
  • Promptly refrigerate a ferment when it’s had it its fermentation time. Try not to leave anything at room temperature once it’s ready, particularly if the room is warm.
  • Find a cool spot to do your fermenting. Fermenting in your greenhouse at the height of summer isn’t a good idea.
  •  Remember to vary your fermentation spot may vary by seasons, and also note that different ferments can also work better in different environments and different temperatures. I get a much less explosive kimchi in my ferment cupboard, but my water kefir prefers a corner spot on my kitchen worktop. But working this out is very much about trailing and taking note. 
  • If you do get Kahm yeast, scrape it off, transfer the ferment to a clean jar (I wipe around the inside the jar with a bit a kitchen roll soaked in ACV to clear off the residue before transferring) and pop it in the fridge, this will stop the yeast from growing.

Free feel to share another other warm weather fermentation tips you use or are thinking of trying out! And if you want to troubleshoot any of your ferments or start a new one and need a bit of support, you can now book a Fermentation Power Hour. These sessions help you to boost your fermenting confidence and ask all the questions you need.

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