Mr Malty Dates

[kappclark]

I am curious how to use the date feature of Mr Malty...it has to do with generations of yeast...let's say for example I harvest 100ml of cake from primary on Jan 1, and I store in fridge

...I do a starter of same slurry on March 1...and get say 150ml of slurry ... what date do I put into Mr Malty - Jan 1 or March 1 to calculate the pitch rate ?? To complicate further, what if I harvest from the March 1 batch in October, and make a starter ,,what date do I use..

Given a good starter, I assume you enter the date of the starter, and not the original batch - right ? Mr Malty is assuming a certain death rate based on age of slurry - right?

 

[LLBeanJ]

Correct. You always want to use a viability date that represents when the yeast you are about to pitch (whether into a full batch or into a starter) were last active and multiplying.

Also, I personally wouldn't use the harvest date as it does not really represent when the yeasts were active and multiplying. Instead, think back to the batch of beer from which you harvested your yeast, determine the date it was brewed/pitched and add a week. That's your viability date (or least, it should be close enough).

 

[kappclark]

Thanks - seems I probably just have a firm grip on the obvious, but either way, the nottingham is hard at work today !

 

[jwalker1140]

You always want to use a viability date that represents when the yeast you are about to pitch (whether into a full batch or into a starter) were last active and multiplying.

Also, I personally wouldn't use the harvest date as it does not really represent when the yeasts were active and multiplying. Instead, think back to the batch of beer from which you harvested your yeast, determine the date it was brewed/pitched and add a week. That's your viability date (or least, it should be close enough).

Respectfully, I'm going to disagree with this. Jamil understands all this about the importance of the viability date, yet his calculator still asks for the harvest date. For all I know, the behind the scenes calculations take the harvest date, rolls it back a couple weeks to determine an approximate viability date, and then calculates the number of active cells from that.

It may not make a noticeable difference on your beer either way, but many people have been using that calculator as designed for years with great results. To me, the notion of plugging in the viability date rather than the date that's clearly asked for seems to over-think the process and it needlessly introduces just one more element of uncertainty.

 

[Calder]

I think the viability calculator for slurry in Mr. Malty is plain wrong! And not worth using. It is way too conservative. If stored correctly, slurry will keep way longer than the calculator predicts.

It is a good reference for fresh yeast and starters.