Saving cells

One of the biggest ongoing expenses in home brewing is buying fresh yeast; it's usual to pay around £6 for a batch of a specific liquid yeast (the best kind) and when you only make small quantities (I only make a gallon of beer at a time) this is by far the biggest proportion of the total. The other ingredients only add up to around £2 to make a gallon of beer. So, I thought I would try and reuse my yeast and harvest it from the gunk left over after the fermentation is done. It's a fairly simple processes, essentially you add water to the gunk and shake it up, then you transfer the milky liquid into separate jars (Kilner jars are good for this) and put them in the fridge. After a while the various components separate out into layers, at the top there is a brown liquid (dilute beer), then a white layer (yeast) and at the bottom a green-grey sludge (waste); see the picture above.

The idea is to carefully pour the spent beer away and then the yeast into a new empty jar leaving the waste behind in the original jar. If you start with four jars you gradually reduce this down to two then to one adding fresh water each time as the volume reduces. This process effectively washes and separates the yeast and you are left with clean cells which can be used in a new batch of beer. Apparently you can safely do this five or six times before contamination starts to introduce off-flavours; if this works then the overall cost comes down to less than £3 per gallon (around 35p a pint) even when using the most expensive and exotic strains of yeast; I wonder if yeast cells could be considered pets?