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With all this talk about stirplates etc FWIW here's a good link for anyone keen on knowing more about calculating specs for Stepping up a multi-stage starter
I've got some oldish yeast sitting in the fridge so I started digging around to try and find out more about the best ways to get the right cell counts from old or small volumes (read: bottle dregs) of yeast.
To date I've used pretty generic advice gleaned from books etc. which is something along the lines of "use 1040 wort....start with 50-100ml....step it up in increments of 5 -10x volume....use a stirplate".
This site lets you to play around with a few key variables, develop more specific step calcs and see the whole process in one screen - a step beyond the MrMalty calculator I thought.
Good site: I'll be using that from now on.
How are you estimating the viability of your bottle dregs? I'm doing the same with my frozen yeast vials, and I never know what number of viable cells to attribute to the 10ml or so that I've frozen. There must come a point at which the number of starter steps and the amount of food has more bearing on the calculation than the original cell numbers?
Thats a damn good question Dougal.
According to the calculator anything older than 4 months only has a 10% or less viability. As for estimating the starting cell count from bottle dregs or a slant - I'm buggared if I know!
I've read somewhere about a "biomass" calculation method which estimates the likely cell growth from the potential for growth in the wort (a function of the starting gravity, fermentability etc) - similar to what you're talking about...but this started to get too theoretical for me so I bailed.
I'm not sure how many homebrewers would have access to a hemocytometer and microscope that you'd need to get an accurate cell count - or even if that level of precision is needed.
I suppose I use the calculator to see the effect of changing variables and help optimise my step up volumes from when I know the dregs I've tried to start up are showing visible signs of life i.e. a 150ml batch of 1040 wort with roused dregs added shows a small krausen. How many cells are in the starter at this stage?? It'd be a wild guess....
I was stuck on the same thing. But I did find on Jamil's MrMalty calculator that you can enter the volume of slurry you have and its consistancy in order to estimate the number of cells.
I would then imagine that using your harvest date as the production date would get you close to your viable number.
It doesn't tell you, and I couldn't work out how it was calculating the volume of slurry required so I couldn't work it out from there either.
Anyone else got an idea?