Yeast starter step up question

I'm somewhat confused on stepping up of starters. I plan to brew Yoopers DFH 60 minute clone on Sunday. I have a smack pack of pacman that was manufactured back in june. The OG of this recipe is going to be about 1.070. Mr Malty calls for 5 smack packs in a 2 liter stater. I have a stirplate and 2 liter flask. How should I go about making an appropriate size stater? I'm thinking doing a 1 liter, 1.5 liter then a final 2 liter would get me close. Or would a1 liter then 2 liter be sufficient?

Given you need about 265Bn cells and you have effectively about 20bn viable cells now in the smack pack if it were me I would do the following.

Pitch it into 1L let it go for 24 hours on the stir plate, allow to settle a bit, pour off about 200ml and top up to 2L. That should result in around 275bn.

Thanks. After doing some more reading last night I think I found a way to manipulate (crudely) MrMalty's pitching rate calculator to determine step sizes. Basically what I did was take what MrMalty said was the viable % of cells left in my smackpack, 10%. I messed with the OG and volume until I got a recommended 1 liter starter with 1 smackpack. This gave me 58Bn cells with my first step. MrMalty says I need 241Bn cells for my starting gravity and batch size. So I took 241 - 58 and got 183Bn that I needed to produce with my second step. Since I'm assumming a fresh smack pack has about 100Bn cells I set my viability to 58% and again messed with the OG until I got a starter that produced 183Bn cells. The starter size came out to be 1.17 liters. So, If I go by this method I'll need to make my first step 1 liter and my second step 1.17 liters. I'll proably just do a 1 liter and 1.5 liter starter and call it good. Does that make sense?? Or am I way off base here with how I manipulated the pitching rate calculator??

To understand stepping you have to understand how yeast grow. Yeast multiply when they are healthy and when each cell builds up enough cell mass it divides. To build up mass the yeast cell needs three things O2, nutrients and sugar, with these the yeast gets fat and healthy and divides. So you say why dont i put my 20BYC in 2L of wort on a stir plate and let it do its thing and keep dividing. Well in theory you could do this however if you dont pitch enough cells in your starter you rusk bacteria getting a foot hold before the yeast can do their job and in the process make the wort more acidic which makes it in hospitaple for bacteria.

Sio we know that yeast need there three elements to reproduce and since the level if nutrients and sugar is known and we will be using a stir plate so O2 is unlimited we can estimate the number of yeast cells by using 1040 wort and standard nutrient levels. Several grouos of people have made starters with known methods and then counted the cell density for us. The reference i first used when doing stepped starters was maltose falcon web site on yeast propogation and maintenance. At this site they estimate a stirred starter has between 180-360MYC/ml so i use 200MYC for my calcs. This gies you a final starter size of around 1.5L.

Step sizes are based of a few things some of it has to do with rate of increase in cell number vs bacteria growth but other factors has to do with yeast training if you make too small a step the yeast may get lazy and only be conditioned to eating simple maltose and not more complex sugars like trimaltose. Reading I have done says step sizes should be in the order of 4 to 10 fold increases in volume. So taking your 20BYC that is equivalent to a 100ml starter so I would do a 500-750ml first step and then go to a 2L second step with a crash cool for 36-48hrs before decant and pitch new wort.

Clem
im doing this on my phone so there is lots of typos sorry but im on the road.

Excellent write up Clem, as usual.

Thanks Clem. That makes sense. So your basically saying instead of doing 1 then a 1.5 liter starter, I would be better off doing a .5-.75 liter first step then a 2 liter second step. Making the step size greater, right??

Spot on too small a step and they yeast will get lazy.

Clementine said:

Spot on too small a step and they yeast will get lazy.

Click to expand...

Thanks again for the info!!! Have .75 liters of starter wort chilling now.