Two yeast growth questions

I'm making a dubbel pretty soon and couldn't get the yeast I wanted, but a friend has a pretty old slurry of this strain. It's about a year old. I want to try building it up slowly, but I'm not sure what size starter I should eventually be targeting.

I'll be pitching 5.5gal of 1.075 wort, and my plan was to pitch his old slurry into 250mL of wort, stir plate for 36 hours, then add 750mL, 36 hours, 1000mL, 36 hours, and see where that gets me. Any objections?

Second, I'm brewing a brown ale soon, pitching 5.5gal of 1.060 wort. I have some slurry I harvested a few weeks ago, and according to Mr Malty I estimate I need about 120mL of this slurry. I have 75mL. What size starter should I make to boost the cell count? I was thinking just 1 liter.

I need to buy that yeast book...

kanzimonson said:

I'm making a dubbel pretty soon and couldn't get the yeast I wanted, but a friend has a pretty old slurry of this strain. It's about a year old. I want to try building it up slowly, but I'm not sure what size starter I should eventually be targeting.

I'll be pitching 5.5gal of 1.075 wort, and my plan was to pitch his old slurry into 250mL of wort, stir plate for 36 hours, then add 750mL, 36 hours, 1000mL, 36 hours, and see where that gets me. Any objections?

Second, I'm brewing a brown ale soon, pitching 5.5gal of 1.060 wort. I have some slurry I harvested a few weeks ago, and according to Mr Malty I estimate I need about 120mL of this slurry. I have 75mL. What size starter should I make to boost the cell count? I was thinking just 1 liter.

I need to buy that yeast book...

Click to expand...

You can make bigger jumps than that, even if you only multiply 4 times the amount. And you need to pitch much more yeast for 1.075. You want to go 250mL to 1L to 4L or more. I would probably pitch into 500mL and go straight to 4.5L.

On the second question, a 1L starter is way too small for anything. Maybe throw that slurry in a 3L starter and have at it.

Just to be clear, I have a stirplate.

I don't really have a concept for how much to grow the belgian strain, but for the brown ale I think about it this way: I currently have about 66% the yeast I need. If I were to buy a healthy smack pack, I would also have about 66% the yeast I need. Therefore the step up should be about the same size, and Mr Malty tells me that's 1L. Even a 1L starter will probably grow too much but I'm okay with barely overpitching... it's not like it will be a whole yeast cake.

In short, I wouldn't need to make a 3L starter for this brown ale unless I had some TERRIBLE viability via old yeast.

I agree w/ dale. You can do bigger bumps. Maybe 500ml to 1500ml/2000ml and you'll be fine.

For a 1.060 I'm not sure 1l is too small. My standard is 1250ml w/ 140g of DME for anything "standard gravity" which I consider under 1.060.

Well, if you had the yeast book it would just tell you not to pitch that slurry.

There is no way the Mr. Malty calculator says you need 120 ml of year old slurry....

You can try pitching it to some very week wort, the viable yeast will stay in suspension, decant this off the trub and let it ferment out and see what you have. Propagate from there. That's about the best you can do.

Read the OP again remilard, you're mixing the answers to two questions

Some more information and updates on this "experiment."

First, I talked some more with the guy who gave me the old yeast. It came from the first generation of fermentation after coming out of the smack pack (not including a starter before that beer). That at least eases my mind about mutation that's due to divergence through generational growth. I'm not saying there couldn't be some mutants in there (from the growth phase of the first beer) but there's a lower chance.

He also specifically mentioned how pleased he was with the thoroughness of his sanitation with this yeast. Take that for what it's worth, but he is a great brewer and definitely a person I would trust to do cleaning and sanitizing for me.

As for age concerns, the best I can do to comfort myself is think in terms of odds. Yes, a significant portion of the stored yeast are dead. But the information that I have suggests that the yeast that are still living are still good. It will just take some work to get them to the levels I need. At least, this is what I'm saying to myself!

As for updates, I decanted the old slurry and pitched into 250mL of starter wort. The addition of the yeast raised the volume to about 350-400mL, which was probably diluted to about 1.025. I deliberately targeted this slightly lower gravity.

It looked pretty ruddy and gross for awhile, but about 36 hours in I started to see some tiny, light bubbles amassing on the surface. I let this go for a few more hours, and then added 1500mL of starter wort and got it on the stirplate. Two hours later and I have a nicely active starter.

I'll judge when things have slowed/stopped, and then I'll chill, decant, and make another 2L starter for the next step. I don't have a bigger flask so my only other option is a 1gal apple juice jug that won't work on my stirplate. I get the impression from Mr Malty's calc that a 4L without a stirplate isn't much better than 2L with one.

Sounds like things are going well. I don't have a stirplate so I can't comment, but it looks good to me.

How's the brown ale coming?

Keep up the hard work!

I've already grown all the yeast I'll need for these two batches. I found a guy on HBT who explained a great way to use Mr Malty to figure out "if I have X amount of yeast, what size starter should I make to yield Y amount?" Here's how:

Let's say I'm making a 1.060 ale, pitching 5.5 gallons. I have a jar of reharvested slurry that is exactly four weeks old from today, and the yeast is very compacted into a 50mL puck. I go to Mr Malty, set the parameters of my beer, set the age of the yeast, go to the "Reharvesting" tab, set the Yeast Concentration to 4.0, set the Non Yeast Percentage to 15.

Mr Malty says that I need 229billion healthy yeast cells, which would be 134mL of my yeast in its current state. I actually have 50mL, or 37% of what I need (50/134). If you multiply 37% by 229billion cells, you find that I have about 84billion healthy cells.

Here's where things get fuzzy. As I understand it, the Mr. Malty calculator works such that a vial of yeast with 100% viability has 100billion cells. So if I have 84 billion cells, this is the equivalent of having one vial of yeast at 84% viability, right? So then I flip to the Liquid Yeast tab, manually set my viability to 84%, set the Growth Factor so that it says I need 1 vial. Doing this, it says I need to make a 1.23L starter with a stir plate.

So I did all this with my existing yeast, and once the starters were finished, I put them in mason jars and let them settle out. Sure enough, if you run the Mr Malty calculator (this time with viability set at 95% since you just made the starter, the mL of yeast it spits out are pretty close to what I have in the bottom of my jar.