That was my question, how do you figure that out? Can you provide a formula? If I have 200 ml of slurry, how can I plug that into a formula that tells me how much glycerine and water to use?
You're way overcomplicating this. I'll see if I can walk you through this.
Final volume is how much liquid you end up with after you mix in the glycerine. Here are a few examples that should help.
Scenario 1
You have 150 ml of yeast slurry. You want to know how much glycerine to add so that the final concentration is 20% by volume. Working with percents is kind of weird. We're shooting for 20% glycerine, so we have to divide the volume of slurry we have by 80% to find out what the final volume would be with 20% glycerine mixed in. If we wanted 30% glycerine, then we would divide by 70%, Here is the equation.
Volume of Yeast slurry / 0.8 = final volume. We have 150 ml of slurry. 150 / 0.8 = 187.5 ml. Now that we know the final volume, we can subtract the amount of slurry we already have (150 ml) to determine how much glycerine we need. 187.5 - 150 = 37.5. So, you add 37.5 ml of glycerine to the 150 ml of slurry that you already have and then freeze it. We now have a final concentration of glycerine of 20%. 37.5 / 187.5 = 0.2
Scenario 2
You have 150 ml of slurry. You want to use this slurry to fill (5) 100 ml vials. You want a final concentration of glycerine of 20% by volume. In this instance, we know what the final volume is going to be, 500 ml, becasue that is what we need to fill all the vials. Here is the equation for this one.
Desired final volume * desired glycerine concentration % = glycerine needed. 500 ml * .20 = 100. So, we add 100 ml of glycerine to the yeast slurry we already have and then add water to top it off at 500 ml. Then you fill the vials and freeze.
Scenario 3
You have 150 ml of yeast slurry. You want to use this slurry to fill (5) 100 ml vials. You want a final concentration of glycerine of 20% by volume. You have a pre-sterillized jar of 60% by volume glycerine solution. You want to know how much of the 60% solution to add to your yeast slurry. Here is the equation.
(Desired final volume * desired glycerine concentration %) / concetration of existing glycerine solution = glycerine solution needed
Our final volume is going to be 500 ml because that's what we need to fill the vials. We want 20% glycerine. Our pre-sterilzed glycerine solution is 60% by volume. (500 ml * 0.20) / 0.60 = ~167 ml. So, we add 167 ml of our glycerine solution to the 150 ml of yeast slurry that we already have. Then we top off with water to get 500 ml. Then fill the vials and freeze them.
Hopefully that helps, I'm not the greatest at explaining things sometimes.
