How Long Should You Ferment Tomato Seeds?

Fermentation is a key step in extracting tomato seeds.

It helps remove the gelatinous sac surround tomato seed. It controls some tomato diseases. It is also a great way to create amazing odours.

But fermentation is very weather dependent. We have had batches that have taken 6 days to ferment. And batches we’ve lost in under 2 days.

Today let’s explore how temperature affects tomato fermentation.

But first a little …

Tomato Seed Saving 101

When Do You Stop Fermentation?

There are two visuals signs that you should stop your tomato seed fermentation

  • Formation of 1-2 inches of white mould at the top of the mix.
  • Seeds have precipitated to the bottom of the container.

If you are fermenting in a glass jar, you can easily see when seed has precipitated. If you are fermenting in an opaque container, you must stir a bit to move the gunk over and see if most seed is no longer floating.

Be careful, if you have very fleshy tomatoes, your juice/seed mix might be too dense for seeds to sink. Your seeds might be ready even though they haven’t sunk.

If you’re concerned that your mixture is too dense. When you suspect your seed should be ready, you can add water to the mix. Then stir and see if the seeds sink.

Be Careful With Water!

Adding water to your juice/seed mix will dilute the nutrients and slow down the fermentation.

Avoid adding much water to your mix when you’re setting it up for fermentation.

Be extra careful about this in the autumn.

Fermenting In The Heat Of The Summer

Our summers are fairly hot. Temperatures are often over 30C. This temperature can really speed up fermentation.

But it depends where you ferment!

When we started, my seed processing area was in the barn. The floor was a huge concrete slab that kept the whole room cooler than outside temperatures. In the hear of the summer, it would take 4 to 6 days for tomato seeds to ferment.

In recent years, we have moved our wet seed extraction into a caterpillar tunnel. We leave tomato seeds in here to ferment. In this situation, the ambient temperature is hotter than outside temperature.

We quickly learned that if we waited 3-4 days in these conditions, seeds would start germinating in the fermenting slurry.

We were not happy to discover this.

We now aim for 2 days of fermentation and are ready to ferment sooner if needed!

This has meant being careful about when we squish our tomatoes.

If we were to squish on Thursday or Friday, it could mean the seeds are ready on the weekend. Farmers should be able to escape the farm on weekends!

So, in the heat of the summer, we always squish tomatoes on Monday or Tuesday to make sure we’ve decanted the seed before the weekend.

Fermenting In The Cool Of The Autumn

At the end of September, it’s a different story!

Ambient temperature is often 15-18 C and nights can be 3-8 C It can take a solid 6 days to get a good fermentation.

We put fermenting crops in the greenhouse for added heat. At this time of the year, the furnace isn’t running. The greenhouse temperature is very dependent on how much sun shines during the day. Overcast days can keep the greenhouse from warming up.

Even in the greenhouse, it can take 4-6 days to ferment at this time of year.

This is when we break our Monday/Tuesday squishing rule, since we have more flexibility when to decant.

In fact, I sometimes prefer squishing on Thursday/Friday, since we likely won’t need to decant until the following Monday/Tuesday.


How do your tomatoes ferment?


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