Yeast slurry, MrMalty.com, and "harvest date"

larsenj · February 17, 2014, 10:47pm

I’m looking to use my yeast slurry (from a 1.047 Helles) for a 1.052 Steinbier. I was trying to use MrMalty.com, but I have a question that I can’t seem to find a definitive answer for.

When using smack packs, it’s easy to know what the “harvest date” is – it’s printed on the package. But for a yeast slurry, I’m not so sure… In this case, I have a 34/70 Helles that was brewed on 26-Jan and began lagering on 15-Feb (while still in the primary fermenter). I’m planning on brewing the Steinbier the 2nd weekend in March and was contemplating just racking the Helles into the the keg on the night before brew day so I could just transfer the appropriate amount of slurry to the new fermenter at that time.

So… What should be considered my “harvest date”? And are there any issues with using yeast slurries that have went through the lagering process?

dannyboy58 · February 18, 2014, 3:42pm

[quote=“larsenj”]I’m looking to use my yeast slurry (from a 1.047 Helles) for a 1.052 Steinbier. I was trying to use MrMalty.com, but I have a question that I can’t seem to find a definitive answer for.

When using smack packs, it’s easy to know what the “harvest date” is – it’s printed on the package. But for a yeast slurry, I’m not so sure… In this case, I have a 34/70 Helles that was brewed on 26-Jan and began lagering on 15-Feb (while still in the primary fermenter). I’m planning on brewing the Steinbier the 2nd weekend in March and was contemplating just racking the Helles into the the keg on the night before brew day so I could just transfer the appropriate amount of slurry to the new fermenter at that time.

So… What should be considered my “harvest date”? And are there any issues with using yeast slurries that have went through the lagering process?[/quote]

I can’t answer your question re: lagering’s affect on the yeast but your harvest date would be the day you rack off the first beer.

If you want to reuse the cake, I’d keep it simple and just remove 1/3-1/2 of the yeast cake then just rack the second beer onto it. Which really makes your harvest date and what Mr Malty has to say irrelevant.

flars · February 18, 2014, 6:53pm

Use the date active fermentation ended.

dobe12 · February 18, 2014, 7:28pm

I usually choose a date a day or two after pitching. The way I figure, it’s just after the yeast is done growing and when the majority of cells are at their youngest. From that point on they are aging.

I would not chose the date you rack of the cake. That timeline could be anything. You could rack after a week, 3 weeks, 2 months… there’s a huge difference there in which there is no way Mr.Malty could account for.

dannyboy58 · February 18, 2014, 9:39pm

[quote=“dobe12”]I usually choose a date a day or two after pitching. The way I figure, it’s just after the yeast is done growing and when the majority of cells are at their youngest. From that point on they are aging.

I would not chose the date you rack of the cake. That timeline could be anything. You could rack after a week, 3 weeks, 2 months… there’s a huge difference there in which there is no way Mr.Malty could account for.[/quote]

You make a valid point.

dobe12 · February 18, 2014, 9:46pm

[quote=“dannyboy58”][quote=“dobe12”]I usually choose a date a day or two after pitching. The way I figure, it’s just after the yeast is done growing and when the majority of cells are at their youngest. From that point on they are aging.

I would not chose the date you rack of the cake. That timeline could be anything. You could rack after a week, 3 weeks, 2 months… there’s a huge difference there in which there is no way Mr.Malty could account for.[/quote]

You make a valid point.[/quote]

I used to think the same as you. Harvest date is the date you harvested the yeast, right? Makes sense. Then one day I was racking a beer off of a yeast cake that had been sitting for a little over month, which is about 2 weeks longer than they normally sit. All of a sudden it dawned on me! “Wait… this generation of yeast grew about a month ago. So isn’t this yeast already a month old?”

I’d love a more scientific answer to this, but I’m now comfortable using 2-3 days after pitching as a starting date.