Wet-seeded crops

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Wet-seeded crops, as the term suggests, are crops where the seeds are inside a wet and juicy fruit when they are mature. The main wet-seeded crops are tomatoes, cucumbers, pumpkins, courgettes and sometimes peppers. Peppers are an exception to the rule as they can be treated as either wet or dry-seeded depending on the techniques you use to process them

Seed ripeness and harvest

A reasonably reliable way of telling if a fruit contains ripe seeds is by its colour. Plants do not want their seeds to be eaten (and therefore spread) by an animal until they are ripe, so unripe fruits are usually green and discreet whereas ripe ones are brightly coloured – think bright red tomatoes and bright orange squash.

Some wet-seeded crops, mainly cucumber and courgette (also green chillies), are harvested for food long before the seeds are ripe inside, whereas others (tomatoes, pumpkins) are eaten when the seeds are at their full maturity. If we want to save seeds from cucumbers and courgettes we have to leave the fruits on the plant to ripen. If left long enough the fruits will grow large and change colour – they tend to go yellow, although it does vary between varieties.

Seeds of the cucurbit family (cucumbers, courgettes, squashes) greatly benefit from a period of post-harvest maturation to achieve the highest germination rates. The fruits should be harvested at maturity and then left in a warm dry place for a few weeks before being processed.

Tomato and cucumber seed fermentation

Some wet-seeded crops have a germination-inhibiting enzyme around their seeds. This is very clever evolution and has come about to prevent the seeds from germinating inside the fruit on the plant, which is warm and wet – ideal conditions for germination. However, if we want to have high germination rates in our seed we need to remove this gel layer and we do this through a process of fermentation.

Tomatoes and cucumbers are the main crops we need to do this with and the process is as follows:

  1. Harvest ripe fruits
  2. Remove the seeds, juice and pulp and put into a jar
  3. Leave the mixture to ferment for 2-3 days in a warm place (22Ā°C is good) – stirring once per day.
  4. Top up the jar with fresh water and give it a good shake
  5. Pour off the pulp making sure not to pour the seeds out too – the good ones should sink which is useful
  6. Top up with fresh water again, and repeat this process until the water is really clean (known as ‘water-winnowing’; see below)
  7. Tip the seeds out into a sieve and then then spread them out to dry in a single layer on a non-porous surface (we use teflon chopping boards)
Tomato seed fermentation

Cucurbit seeds

It is also possible to treat cucurbit seeds (pumpkins, courgettes etc) with a light fermentation for just 24hrs. This can help break down the pulp which is attached to the seeds. However, this is a contentious issue and not all seed growers do it. We have had great success with it but only with some varieties, as some have seeds that sink and others have seeds that float and there is not much pattern in it.

If you choose not to ferment your cucurbit seeds then you can just scoop out all the seeds and their pulp into a bucket with an ice cream scoop, mix with some water and then if the seeds float you can skim them off with a sieve and if they sink you can water-winnow them (see below).

On a small scale, if just few seeds are needed, then you can just pick them out of the cavity in the fruit when you are cooking them.

Pepper wet-seed treatment

There are a few ways to process pepper seeds. On a small scale the seeds can just be removed from the flesh and dried. On a larger scale many fruits can be roughly chopped and then put with water in a blender – with blunted blades, so as not to chop the seeds. The good seeds will sink to the bottom and the bad/small ones will float, the mix can then be water-winnowed.

Water-winnowing

Drying wet seeds

Drying wet-seeds thoroughly is a particularly crucial part of the process. As they contain a lot of moisture they can develop mould if not dried quickly.

The most crucial thing to ensure is good airflow around the seeds, and to do this we need to spread the seeds out in a single layer, ideally on a porous material – an old sheet or tea towel works fine, as does insect mesh spread over a frame. For small quantities of tomato and pepper seeds we use teflon chopping boards, which although not porous work really well as the seeds are small enough that they dry quickly compared to large seeds like pumpkins.

Do not dry your seeds on tissue paper! It will stick to them afterwards and can be very annoying.