Tomato seeds for future generations, in pulps of all colours. Banana Legs (left), Black Prince (top), Douce de Picardie (right), and Caro Rich (bottom).
Bugger the credit crunch ... you need never pay for a packet of tomato seeds again if you adopt the age-old practice of saving your own. Even a single fruit will yield enough seeds to last you for years (or to share with your friends) and they can quite easily stay viable for 10 years or more, so it's really well worth doing. As tomatoes are naturally inbreeding and self-pollinating, you can get away with growing a small number of plants and saving just a small number of fruits. If you save seed from F1 hybrid varieties they won't come true to type, but the results can be interesting in their own right. Many commercial F1 hybrids are a rip-off anyway, unless you want to use them to develop your own versions.
There are basically two ways of saving seed from tomatoes. The recommended way is to ferment them in their own gel, which works very well but is a little fiddly and icky. And then there's the quick bodge-job method, which is often frowned upon but works perfectly well in my experience. Personally I use both ... the proper method for larger amounts (saving seed from two fruits or more) especially if I intend to give them away to others, and the bodge-up method for small amounts (one to two fruits).
Either way, the ideal thing is to use tomatoes that are over-ripe ... past the point where you'd want to eat them. I often compromise by using only slightly over-ripe fruits, cutting off any bits which have gone manky and stewing up the remainder in a pan with olive oil to make a lovely sauce. That way nothing gets wasted. You CAN save seed from tomatoes which are still green, but the less mature they are the more risk there is that the seeds are immature, in which case they may not germinate.
If possible, avoid saving seed from plants suffering from blight. I say "if possible" because frankly the blight problems have become so bad in the UK it's almost impossible to grow a totally blight-free crop these days. If you have a plant you really want to save seed from and it has blight, save seed as early in the season as you can (even if the fruits are not fully ripe) and choose the least affected fruits.
Even with the more elaborate method, saving tomato seeds is very easy. Just try not to use the unladylike language I did this morning when I dropped a load of partially dried Caro Rich seeds all over the carpet (it had to be a beige carpet, didn't it?)
The fermentation (recommended) method
Slice open your chosen fruit(s) and spoon out the seeds, complete with their surrounding gel, into a small jar or container. Clear glass is ideal so that you can see what's going on in there during fermentation, but any container will do ... a jam-jar or a plastic yoghurt tub. The little glass dishes you get with overpriced puddings from Waitrose are ideal. Whatever you use, it needs to be narrow enough to create a bit of depth when you put the seeds and gel into it. Most people add a small amount of water. It doesn't make a lot of difference either way, but a bit of water seems to help things along. Use a separate dish for each variety you're saving seed from (that should be obvious but I'd better say it anyway).
Cover the jar with a scrap of foil and leave it somewhere like a windowsill for about two to four days.
After a day or two you should notice some changes happening in the jar. Bubbles, for one thing. They may not be active fizzy bubbles, but there should at least be some bubbles hanging around in there. The other thing you'll get is a hideous crust of mould over the surface. This is entirely normal and should be left undisturbed.
I'm fascinated by the diversity of mould that appears on tomato pulp. Sometimes it's a pale waxy yeast-like gunge over the surface, and sometimes it's more bluey patches, or little white hairs. Occasionally you get the whole jar filled up with soft dry fluffy stuff like grey candy floss, which flexes to the touch like a delicate sponge.
After a few days you can tip the yukky stuff out and retrieve your seeds. It's difficult to give a time scale for when to do it, it's not a precise science. Allow the mould to grow right over the surface, and it should be ready shortly after that. The main thing is not to leave the seeds fermenting too long, or they will start to germinate and be ruined. Fermentation happens much faster in warm conditions, and can be ready in as little as 24-48 hours in a hot climate. More usually though (in European countries) 3, 4 or 5 days is about right.
When you're ready to decant the slop, the first step is to gently peel back the mould layer with a teaspoon. Sometimes it just peels back as easy as anything like custard skin, other times it's more irksome. Either way, there will probably be some seeds sticking to the underside of it. You have two options at this point. You can go "uuuuuuuuurrrrrrgh!" and lob the whole lot straight in the bin. Or you can carefully hold the mould disc aloft and scrape the seeds off with a teaspoon. It all depends on how precious the seeds are and how squeamish you are about mould.
Once it's denuded of its mould layer, slop out the contents into a fine-meshed sieve or a tea-strainer, and gently wash it under a slow-running tap. It can take a bit of rubbing to get rid of all the fleshy pulp, but eventually you should be left with a strainer full of nice clean wet seeds. I usually leave them to dry in the tea-strainer, but you can dump them out on a plate. It's not a good idea to put them onto kitchen roll or paper because they may stick to it, though it's OK to put the strainer down on top of some kitchen roll. Either way, the seeds will clump together as they dry and it's a good idea to give them an occasional rub to separate them.
Within a few days you'll be left with the familiar cute fluffy little seeds ready for packeting up.
If you're saving more than one variety, take care not to muddle them up. Most are impossible to tell apart. Make sure there aren't any seeds from a previous batch clinging to the sieve or teaspoon.
Why go to all this bother, you may ask? Well, the gel around the tomato seeds contains a chemical to inhibit germination (very useful to prevent the seeds germinating within the fruit as it ripens). The fermentation method mimics nature's processing of the seed by breaking down the chemicals in the gel, making use of the naturally occurring Oospora lactis which is responsible for the rapid rotting of fruit, and enabling the seeds to germinate freely. In the process it rids the seeds of many bacterial diseases.
The Quickie Bodge-Up Method
Just scrape the seeds out of the tomato straight onto a piece of kitchen roll (paper towels in the US). Spread them out as thinly as you can, and leave the sheet somewhere well ventilated for a few days to dry. Write the variety name on there, fold it up and store it in a seed envelope.
Here's one I prepared earlier
The seeds will be stuck glue-like to the sheet and may not ever want to come off, but that's OK, you can just tear round them at planting time and sow them with the paper still attached.
This has got to be one of the easiest seed saving methods around. It has two potential disadvantages. One, it doesn't kill off any bacterial diseases that may be lurking around the seeds, and two, it doesn't remove the chemical that inhibits germination. But in practice it isn't usually a problem. I've never had any germination problems with seed saved in this way, and they stay viable for years. Maybe the chemical does break down on the kitchen roll by the time you're ready to sow the seeds. The threat of seed-borne disease is small if you select fruits from healthy plants. So if this is really the only way you'd want to save tomato seeds, go for it I say.