What's the difference?

[FuzzySteve]

Rightly of wrongly, I've decided to pursue the liquid yeast route by pitching a vial of WL East Midlands into a demijon with 4 litres fresh wort (at1.046) from yesterday's brew to bring it on and harvest as outlined here;

http://uk-homebrew.tripod.com/id46.html

My confusion lies in why harvesting the yeast in this way and keeping it for up to 6 months at between 2-5°C is any different to rinsing the yeast and trub and harvesting the yeast post-fermentation, which appears to be only viable for a couple of weeks.

Have I got my wires crossed somewhere? Or is there a reason why the two methods result in such different viability time frames for the yeast?

 

[Good Ed]

There isn't any difference; on a home brew scale we are just trying to keep the yeast as viable as possible. By making a starter all you are doing is growing the number of yeast cells, so however you harvest yeast, you are saving a quantity of yeast cells and then storing them for future use. If you do this by storing in the fridge or even by alternative methods, then you are going to get some deterioration over time. So what you do is to take whatever you have stored and then make a starter with a suitable volume of wort to get the number of viable cells for your brew, Mr Malty is good for this.

The Yeast book by Chris White and Jamil Zainasheff is invaluable for understanding the process in more detail.

 

[FuzzySteve]

Thanks Ed. It seems as though a good book may be in order if I embark upon this yeasty path!

 

[johnnyboy1965]

What I do with expensive liquid yeasts is :-
make a starter using half the vial, up to whatever you need. eg 1li...put the remainder of the yeast vial back in a fridge and label (Never Been Fermented)
Pitch starter as required, brew, ferment etc...then I wash the trub and collect the yeast, label this "1st Gen" and date
Next time you want to brew with this yeast, use one of those labelled "1st Gen"....brew, ferment, wash, collect and label "2nd Gen" and date
The next time you brew make a starter using the original 1/2 vial brew ferment, wash and label "1st Gen" and date.
At this point you will always have at least 2 "1st Gen" and at least 2 "2nd Gen" yeasts.
Its then a matter of stock rotation and you will always have a fresh yeast to fall back on.
I hope this makes sense.
Im currently brewing a bitter using "7th Gen" yeast (WLP 007)