Yeast Harvest - The Easy Way
There are lots of complicated methods out there for harvesting your own yeast and reusing it on multiple beers. The simplest and most foolproof method out there is to simply schedule your brew days and transfers properly and dump the new wort on the old yeast cake. This isn't always the best solution though and it limits you to brewing a (usually) darker beer on the same type of yeast. Another method is to "wash" the yeast. This involves trying to harvest just the yeast from the cake and is a terrible idea. It is messy, not very sterile and unreliable. It works.. but what I recommend is to just take some from your starter!
Following my instructions to make a starter with your stir plate (or buy your own) will produce the best results, so make sure to check that out. Once your starter has eaten all the sugars (about 3 days) then you can get ready to harvest. A day before you're going to harvest, put your jug of yeast in a fridge that is as close to 34 F as you can get it. This will remove most of the yeast from suspension.
Materials
2-3, 8oz mason jars with lids
pot to boil them in with a lid
tongs
Stir Plate
Procedure
Submerge the jars and lids in water and bring to a boil, boil for twenty minutes. Once done, immediately take out the jars and keep them filled with the boiled water, cover and let cool completely. (If you're making beer today, then you will only need two jars, if not then you can fill all three)
Gently pour off 95% of the liquid over the "yeast cake" that you formed by chilling the starter. With a sanitary funnel, pour in the water from each jar and shake the hell out of it. Now you can pour the yeast filled water into each jar. If you're making beer the same day you can pour the last jar's worth in to the bucket! If you forget to chill the starter or have no time to, simply pour half of it into the bucket of wort, then chill it. You can still get two jars of plenty of yeast the next day using the method above.
In the end you will have at least two jars of whatever yeast you just used. If you do this often you will quickly grow a stock of all your favorite yeasts! I rarely have to buy new yeast and NEVER have to buy Nottingham ! Save some serious cash for just a tiny bit of effort. If you are sterile and do a good job keeping these jars cold they can last 3-6 months easily, hell I even used one that was a year old once! Just be mindful of the color change, don't let it get too peanut butter-y. To make sure you don't thrown crap yeast in your next beer, it's always a good idea to make a starter! This way you can not only test the yeast's health and smell it you can harvest it again and continue to keep your stock in a good rotation.