|Pepper Seeds in the "Sink or Swim" Test of Doom!|
Peas and beans are the easiest to save. I call it the "lazy gardener" method. Basically you just forget to pick the pods until they get HUGE then you let them dry being sure to remove them before the first frost (and letting them dry out indoors) until the seed pods are tan and papery. Then you remove the seeds from the pods and let dry in a well-ventilated area for a few more weeks. Taadaa! Some people test their seeds to see if they will germinate at this point, but I don't.
Tomatoes are the really fun ones; you need to ferment them. I truly love lacto-fermentation so fermenting the seeds wasn't too odd for me. Basically you remove the seeds from the fruit and put them with their pulp into a container. If you don't have a ton of seeds, add a bit of filtered water to cover then put a paper towel or other breathable cloth (I use a coffee filter) over your container and let it go. Stir once a day for 2-3+ days and you should seed a white film/fungus form on the top of the liquid. This fungus eats the pulp making it easier to separate the seeds AND as a bonus, it kills any diseases that may be harboring on them. Once you have a nice growth of fungus you want to gently spoon it off and then rinse your seeds. At this point it is a good idea to do the "sink or swim" test. Put your seeds in a glass and cover with water. Viable seeds will sink, non-viable seeds aka "duds" will float. Spoon off the floaters and pour your seeds into a fine mesh sieve shaking out as much water as possible then let dry on a paper plate or other breathable surface.
Peppers are similar to tomatoes except I don't ferment them. I read that some people do but, meh. The "sink or swim test" as demonstrated in the picture above is really necessary for peppers and is a good idea for pretty much any seed before you dry it unless...
You dry it directly on the plant! With herbs in the umbellifer family (dill, cilantro etc.) I let the plants go to seed, dry out and then I cut off the whole plant and dry it indoors and collect the seeds after a few weeks. This is also a super lazy method but it works for me.
Those are pretty much all the seeds that I have successfully saved. I tried lettuce seeds one year but those suckers are tiny. I have never had my kale or chard go to seed but when they do I will be ready for them.