dachbach said:
I've been reading washed yeast/starter threads for awhile and it seems that people in general recommend making a starter with washed yeast even if you have enough viable yeast to begin with. The reason I'm curious is that I don't brew that often and have no need for a bunch of mason jars of yeast sitting in my fridge forever.
I have three mason jars that each have about 2 oz of compacted slurry at the bottom. They've been in the fridge for almost 2 weeks. I'm going to brew again this weekend so they'll be right at 2 weeks old.
Using the default thickness and non-yeast percentage on Mr. Malty tells me I need 126 ml, which is 4.26 ounces.
Can I just decant most of the liquid off the three mason jars and pitch two full ones and a 1/4 of the last one?
Or is it really that necessary to make a starter first?
According to some podcast I listened to from Jamil and John Palmer...
Harvested yeast is good for up to 2 weeks (in the fridge). After about a week, yeast begins to eat it's "reserves." Thus, if you wait more than a week from harvesting and pitching - you should make a starter to wake up the yeast and make more healthy cells. (you can get away with 3 weeks with some strains, but definitely make a starter if so)
To make a starter from harvested yeast, you need to figure out how much yeast you have. I like yeastcalc.com, but Mr Malty is good too. I find that my yeast slurries are typically in the 10-20% range. I suggest checking out this page from WYEAST:
http://www.wyeastlab.com/com-yeast-harvest.cfm
Buy some WYEAST yeast nutrient and put it in another container - the container it comes in is identical to the containers used in the yeast slurry percentage chart. (Note: this is a relatively standard lab tube - they are available elsewhere I imagine). When you harvest your yeast, shake it up real good and fill the wyeast container with a sample (fill it to the top). Chill it overnight and the next day you can calculate how much yeast you have (using the chart on the wyeast page). For this reason, I like putting my yeast in a starter flask because it tells me how many ml I have of the entire starter.
wyeast says 40-60% slurry is 1.2 bil per ml. Mine is typically about 10% - if you cant measure your yeast, i would assume 10% as well. divide .10 by .50, and then times that by 1.2: ((.10/.50)*1.2). This gives us the actual number of cels per ml.
Using the billion cells per ml number, you can figure out how many ml you need to reach your desired cell count as calculated by mr malty or yeastcalc (# desired cells/observed cells per ml)
If you ever want to pitch recently harvested yeast (that doesn't need a starter)..
you divide your observed slurry percentage by .50 and multiply the result by 1.2 and multiply that result by the ml of your harvested yeast. (((.10/.50)*1.2)*ml)
This will give you the total cell count of your harvested yeast (in billions - so a result of 400 means 400 billion). Now you can use the previous formula (# desired cells/cells per ml) to find out how many ml you need to meet yeastcalc/mr malty's recommendation...no starter needed!