Fermentation Process

Why bother with the fermentation process? 

The fermentation process of seed cleaning and saving is recommended for pulpy vegetables like tomatoes and cucumbers. 

There are 3 main reasons why you should use the fermentation process for pulpy seeds:*

  1. It separates the pulp from the seeds.
  2. It destroys any germination inhibitors in the surrounding gel.
  3. It kills any bacterial fungal pathogens that may otherwise be transferred to the seeds.

* From The Complete Guide to Saving Seeds, Robert Gough and Cheryl  
Moore-Gough. pg. 45.

What is the fermentation process? 

  • The fermentation process is used for pulpy seeds from produce like tomatoes and cucumbers. 
  • The process involves squeezing the seeds, pulp and juice into a jar and allowing it to sit UNCOVERED and ferment over 5 to 7 days.
  • Be prepared for a bit of odour (rotting smell)and possibly fruit flies towards the end of the fermentation process.
  • After 5 to 7 days, begin the rinsing process. Fill the jar partway with water and carefully scoop off the filmy, moldy layer that rises to the top. Then continually fill and empty the jar of water until only the seeds that SINK remain. Any seeds that float are typically unviable.

What you’ll need for the fermentation process…

  • One or three of your best looking tomatoes from the same variety (more for cherry tomatoes)
  • Clean medium or large mason jar
  • Cutting board or other clean work surface
  • Sharp knife
  • Paper towels
  • Mesh window screen (with frame) or fine mesh colander (one for each variety)

Step-by-step fermentation process for tomatoes:

Step 1: Select your best-looking tomatoes

  • Choose one or ideally up to three of your best looking tomatoes to allow a diverse selection of seeds (more for cherry tomatoes).

Step 2: Get a mason jar and a sharp knife and start cutting

  • Get a clean medium to large mason jar and a sharp knife.
  • Cut your tomatoes lengthwise to expose the seeds and pulp. You may cut into quarters for larger tomatoes.

Step 3: Start squeezing!

  • Starting squeezing the seeds, pulp and juice of the tomatoes into the jar. The wetter the mixture the better for the fermentation process.
  • You may use your knife to poke the pulpy inside to help release the seeds.

Step 4: Let the fermentation begin!

  • Allow your jar to sit on a counter, uncovered and undisturbed for 5 to 7 days. The back of a kitchen counter works well.
  • You’ll notice some odour and possibly fruit flies after a few days. You know it’s working!
  • Don’t allow them to sit beyond a week as they may begin to germinate!

Step 5: Start the rinsing process

  • Fill the jar about halfway with water, swirl around and remove the floating bits with a spoon. You may also transfer the seeds to a larger jar for this process.
  • Keep filling and emptying water until the water is clear and only the sinking seeds remain. This may take up to 10 times.

Step 6: Start the drying process

  • Once the seeds are completely cleaned, pour them onto a clean mesh screen or fine mesh colander.
  • Using your finger or a spoon, spread the seeds as much as possible to allow them to dry best.
  • Be sure to label your drying seeds, especially if you are drying several varieties.

Step 7: Storage

  • Allow the seeds to COMPLETELY dry before storing. Usually a week to two weeks will do. 
  • The seeds may peel off the mesh like a sheet. Simply and carefully crumble them between your fingers until they are separated.
  • Preferably store them in paper envelopes in a dry location.