I have always generally used Mr Malty's pitching rate calculator to calculate the volume of starter required for a specific OG and batch size: http://www.mrmalty.com/calc/calc.html
However, considering that I now subdivide my yeast packs into 5 x 20 ml tubes, I have been wondering how to properly step up a yeast starter to achieve the recommended pitching rates.
I know a lot of people advocate the use of stepped starters, however, after some reading, I get the feeling that most people just wing it with regards to volumes and cell counts. Most seem to keep to the basic rule of a max 10 fold increase in volume, however the actual pitching rates after multiple steps are anyone's guess.
Anyway, I have been working on a spreadsheet that allows you to calculate the amount of yeast grown in a stepped starter.
Essentially I played around with Mr Malty's yeast pitching calculator and managed to extract some of the raw data in terms of "step up ratio vs growth rate". This is essentially the scientifically determined data that most yeast calculators are based on. The spreadsheet I have developed allows you to input the starting yeast volume and the step up starter sizes and it determines final yeast count at the end of each step.
Note - At this stage, the spreadsheet is only a draft. I am sure I will get plenty of feedback (good and bad) which I am sure will change some things. Note that it is also only based on a "stir plate" starter at this stage
View attachment Stepped_Starter_Calculator.xlsx
To explain the workings of the spreadsheet I thought a quick explanation with an example may help.
Let's say I have 20 ml of 3 month old yeast in the fridge. I have assumed that the yeast has a 50% viability. This will depend on many factors, but lets assume 50 % (it can be changed in the spreadsheet anyway).
I want to make a 44 L batch of 1.065 Ale. Mr Malty says that I need 523 Billion yeast cells for a correct pitching rate.
I then set up the spreadsheet follows:
Step 1:
Original yeast volume 20 ml
Viability - 50%
o This calculates as 10 billion viable yeast cells or 10 ml of viable yeast (50% of the original 20 ml).
Starter Volume 100 ml
o This is a step up ratio of 10 (10 ml of yeast into 100 ml of wort)
o A max of 10 is recommended by some sources, but some use 5, and some use more.
o I try to stick to around 10 for each step.
o Note that a step up ratio below 4 will currently not work, as I don't have any data for below 4.
The step up ratio is then used to determine the growth rate (based on the data extracted from Mr Malty).
Final yeast count at end of first step is then 23.167 billion cells (or 23.167 ml of yeast)
Step 2:
Wort Addition 150 ml
o This is adding 150 ml of fresh 1.060 wort to the same starter (to give 250 ml of 1.040 total volume)
o The spreadsheet calculates the required OG of the addition for you to achieve 1.040.
o This achieves the same result as decanting off the spent wort (beer) and filling with 250 ml of 1.040 wort. It just saves a lot of mucking around.
o Note that the fermented starter is also assumed to have a FG of 1.010
23.167 ml into 250 ml is a step up ratio of 10.8
Final yeast count is 55.340 billion (55.340 ml)
Step 3:
Wort Addition 300 ml (1.065 Wort which gives a 550 ml starter).
Step up ratio of 9.9 which achieves 127.63 billion cells
Step 4:
Wort Addition 600 ml (1.068 Wort which gives a 1150 ml starter).
Step up ratio of 9 which achieves 282.49 billion cells
Step 5:
Wort Addition 600 ml (1.098 Wort which gives a 1750 ml starter).
Step up ratio of 6.2 which achieves 531 billion cells CLOSE ENOUGH !!
So essentially, for a given staring yeast volume and viability, I just play with my wort additions to achieve:
A step up of around 10 or less
the recommended pitching rate after as few step ups as possible.
Just to convince the sceptics, the spreadsheet predicts the same results as Mr Malty does (within 10 %). This can be verified (in an arse about face way) by doing the following:
In Mr Malty Put in the following data:
25 L of 1.055 Ale with a single pack of 70 % viable yeast (I'm using random numbers to demonstrate).
Mr Malty recommends a pitching rate of 253 Billion cells, and a "stirred" starter of 1.96 L
In the spreadsheet this can be verified by using the first step up calculator.
Put a 100 ml of yeast at 70% viability into a 1960 ml starter
Final cell count is 255 Billion cells which is pretty much the same as Mr Malty
Or for a similar check:
Put in the following data into Mr Malty:
40 L of 1.080 Lager with 80 % viable yeast
Mr Malty recommends a pitching rate of 1155 Billion cells, and a "stirred" starter of 12.99 L with three packs of yeast.
In the spreadsheet this can again be verified by using the first step up calculator.
Put 300 ml of yeast (3 packs of yeast) at 80% viability into a 12990 ml starter
Final cell count is 1159 Billion cells which is again pretty much the same as Mr Malty
The main reason for the small difference is that I only have discrete data points for the "step up ratio vs growth rate". The unknown data is determined through linear interpolation between the data points which gives a small amount of error.
Anyway, hopefully I haven't confused you all. The spreadsheet is in a draft stage, but seems to work as expected, and could be a good tool for me and hopefully others. I am hoping for some independent verification of the methods as well as the spread sheet. A few short comings thus far such as, only for stirred starters, and growth rates for step ups below 4 times are very hard to find.
Anyway, feel free to comment good or bad. Any potential improvements will also be noted.
However, considering that I now subdivide my yeast packs into 5 x 20 ml tubes, I have been wondering how to properly step up a yeast starter to achieve the recommended pitching rates.
I know a lot of people advocate the use of stepped starters, however, after some reading, I get the feeling that most people just wing it with regards to volumes and cell counts. Most seem to keep to the basic rule of a max 10 fold increase in volume, however the actual pitching rates after multiple steps are anyone's guess.
Anyway, I have been working on a spreadsheet that allows you to calculate the amount of yeast grown in a stepped starter.
Essentially I played around with Mr Malty's yeast pitching calculator and managed to extract some of the raw data in terms of "step up ratio vs growth rate". This is essentially the scientifically determined data that most yeast calculators are based on. The spreadsheet I have developed allows you to input the starting yeast volume and the step up starter sizes and it determines final yeast count at the end of each step.
Note - At this stage, the spreadsheet is only a draft. I am sure I will get plenty of feedback (good and bad) which I am sure will change some things. Note that it is also only based on a "stir plate" starter at this stage
View attachment Stepped_Starter_Calculator.xlsx
To explain the workings of the spreadsheet I thought a quick explanation with an example may help.
Let's say I have 20 ml of 3 month old yeast in the fridge. I have assumed that the yeast has a 50% viability. This will depend on many factors, but lets assume 50 % (it can be changed in the spreadsheet anyway).
I want to make a 44 L batch of 1.065 Ale. Mr Malty says that I need 523 Billion yeast cells for a correct pitching rate.
I then set up the spreadsheet follows:
Step 1:
Original yeast volume 20 ml
Viability - 50%
o This calculates as 10 billion viable yeast cells or 10 ml of viable yeast (50% of the original 20 ml).
Starter Volume 100 ml
o This is a step up ratio of 10 (10 ml of yeast into 100 ml of wort)
o A max of 10 is recommended by some sources, but some use 5, and some use more.
o I try to stick to around 10 for each step.
o Note that a step up ratio below 4 will currently not work, as I don't have any data for below 4.
The step up ratio is then used to determine the growth rate (based on the data extracted from Mr Malty).
Final yeast count at end of first step is then 23.167 billion cells (or 23.167 ml of yeast)
Step 2:
Wort Addition 150 ml
o This is adding 150 ml of fresh 1.060 wort to the same starter (to give 250 ml of 1.040 total volume)
o The spreadsheet calculates the required OG of the addition for you to achieve 1.040.
o This achieves the same result as decanting off the spent wort (beer) and filling with 250 ml of 1.040 wort. It just saves a lot of mucking around.
o Note that the fermented starter is also assumed to have a FG of 1.010
23.167 ml into 250 ml is a step up ratio of 10.8
Final yeast count is 55.340 billion (55.340 ml)
Step 3:
Wort Addition 300 ml (1.065 Wort which gives a 550 ml starter).
Step up ratio of 9.9 which achieves 127.63 billion cells
Step 4:
Wort Addition 600 ml (1.068 Wort which gives a 1150 ml starter).
Step up ratio of 9 which achieves 282.49 billion cells
Step 5:
Wort Addition 600 ml (1.098 Wort which gives a 1750 ml starter).
Step up ratio of 6.2 which achieves 531 billion cells CLOSE ENOUGH !!
So essentially, for a given staring yeast volume and viability, I just play with my wort additions to achieve:
A step up of around 10 or less
the recommended pitching rate after as few step ups as possible.
Just to convince the sceptics, the spreadsheet predicts the same results as Mr Malty does (within 10 %). This can be verified (in an arse about face way) by doing the following:
In Mr Malty Put in the following data:
25 L of 1.055 Ale with a single pack of 70 % viable yeast (I'm using random numbers to demonstrate).
Mr Malty recommends a pitching rate of 253 Billion cells, and a "stirred" starter of 1.96 L
In the spreadsheet this can be verified by using the first step up calculator.
Put a 100 ml of yeast at 70% viability into a 1960 ml starter
Final cell count is 255 Billion cells which is pretty much the same as Mr Malty
Or for a similar check:
Put in the following data into Mr Malty:
40 L of 1.080 Lager with 80 % viable yeast
Mr Malty recommends a pitching rate of 1155 Billion cells, and a "stirred" starter of 12.99 L with three packs of yeast.
In the spreadsheet this can again be verified by using the first step up calculator.
Put 300 ml of yeast (3 packs of yeast) at 80% viability into a 12990 ml starter
Final cell count is 1159 Billion cells which is again pretty much the same as Mr Malty
The main reason for the small difference is that I only have discrete data points for the "step up ratio vs growth rate". The unknown data is determined through linear interpolation between the data points which gives a small amount of error.
Anyway, hopefully I haven't confused you all. The spreadsheet is in a draft stage, but seems to work as expected, and could be a good tool for me and hopefully others. I am hoping for some independent verification of the methods as well as the spread sheet. A few short comings thus far such as, only for stirred starters, and growth rates for step ups below 4 times are very hard to find.
Anyway, feel free to comment good or bad. Any potential improvements will also be noted.