I was just looking at the pitching calculators over at Brewer's Friend. How can the Braukaiser Stir Plate recommendation differ so dramatically from the Chris White recommendation? For my particular pack of yeast, which is a few months old, BK says I can get to 322 billion cells with a 2L starter. CW says this only makes 21 billion cells.
Seems extremely low ball if the yeast was stored properly...but if I were going to buy a few month old pack of liquid yeast, I would opt for something like a Gigayeast pack that starts at 200 billion cells. Good luck
It's something I bought a few months back and didn't get the chance to use. I would never intentionally buy an old yeast pack. I was trying to decide whether I really should buy a new pack of yeast. Which would mean mail order. But more to point, what could these two calculators be assuming so differently to lead to such drastically different estimates?
Probably a stupid question, but you are inputting a stir plate for both growth models, right? A lot of places to go wrong (input incorrectly) on that calculator, imho.
If you scroll further down the BF calculator page, there is quite a bit of text that explains the different parts of the calc, and it does address the calculated dif btw Kaiser and White. Brewers Friend is the one I've always used so I just go with it and adjust expectations and predictability over time accordingly based on results. For me, since I get liquid yeast shipped to me 95% of the time (the closest LHBS to me that would have fresh yeast is 2 hours 1 way, I do plan on taking advantage of that when I know I'll be in the area), pitching rate calculators are the biggest crapshoot, even ignoring the inherent assumptions that the calculator uses. It should be refered to as a "best case scenario estimator", instead of a calculator. The most important factor, the actual real viability of the cells in the pack, is completely unknowable to us normal folks. A brand new pack that sat in a 120F delivery truck for a day or 2 vs. a 3 month old pack that stayed cold the whole time will lend you very dif results from the calculator. And for my location, a hot delivery truck is 7-9 months out of the year. What I end up doing is using the BF calc as is for general consumption beers and beers that are good to go even with a little extra yeast esters. For comp beers, those that I want my best effort, packs (or general consumption beer starters) that are old or trashed, I make a starter and then estimate cell count by measuring the creamy fresh yeast that settle on top. Then plug that into the calc and go from there with a second step. It's the best way for me to feel a little more confident that I'm in the ballpark.
Thanks, I did see that since my last post. It explains where the models came from, but not really which to use under which conditions or why they could lead to such different answers. Clearly at least one of the models is seriously flawed at conditions of low starting yeast counts. While your point that the most unknowable thing is the yeast viability is well taken, that is not calculated by the models, so they are fed the same thing. It only means that whichever model you chose, the prediction is a crapshoot because of yeast handling. For my immediate practical question of how to proceed on this specific batch, I guess paying $7 plus shipping and handling for fresher yeast is the way to go for peace of mind. Placed that order last night.
A nice thing about yeast propagation is that the final cell count is not linear with the starting cell count, i.e. the (accidental) change in inoculation rate also influences the growth curves. To illustrate, I ran a few numbers through Yeast Calc, which is a nice calculator when you want to see some of what's going on inside. Let's say you think you are starting with 80B cells, and you need 277B cells, so you do a 2L Stirplate (J.Z. formula) starter. The modeled result is 277B cells. Now let's say you really only had 40B cells (half of what you had assumed). The result will then be 190B, which is fairly significantly more than just half of the original assumed result of 277B. Or say you really had 160B cells (double what you had assumed). The results will then be 403B, which is fairly significantly less than double the original assumed result. In other words, yeast are somewhat forgiving (within reason) of our inability to know precisely our starting cell counts. I'm not saying it's not important to do our best to estimate the starting count, just that there's a little wiggle room.
Thanks for directing me to one more calculator to add to the confusion! YeastCalc appears to assume much greater survivorship with time than the MrMalty and Brewer's Friend calculators. However, both yeastcalc and the Brewer'sFriend are somewhat in agreement on what I need to do to the get to a desirable pitching rate, with Kai's model. This particular dilemma has led me to an epiphany of sorts. One of the important aspects of repitching my own yeast (which I only rarely have done and maybe would like to do more regularly) is that I am much more in control of the yeast storage conditions. Even if I do not do cell counts, I could at least establish internal consistency on viability that is not possible if I am having yeast shipped to me.
Try to find an affordable microscope on ebay or whatever and count your cells. We go to lots of trouble to try and hit OG and calculate IBU and pH etc etc that the guesswork with yeast is ridiculous. The only other things you need are a hemocytometer (which is dead cheap) and some methylene blue (also cheap) and it's not really that difficult. Sorry if this is a bit off topic but it's at least worth considering.
The science geek in me likes the idea. The lazy dude in me thinks it is typically unnecessary. I've got a couple hundred batches under my belt, or so, and they seem to do pretty well just based on starters made from packs of yeast with uncertain viability. But for cases where one is scraping the bottom of the barrel, so to speak, like a 4.5 month old pack of yeast or trying to culture from bottles, there is definite utility here. Turns out I do own this gear, as I did enough microbiology in grad school that it made sense to buy my own scope. And no, I haven't used it since then. If I ever do some of the home remodeling work that I have in mind, I will have a room in my house set up for more beery endeavors, but for now, my scope remains boxed up in the basement.
As for any investment in gear you have to decide if it will be worth it or not. I was lucky and got an old microscope for free. I have been using it as I've been experimenting with pitch rates with certain belgian yeasts (some that I have cultured from bottles) which can be more sensitive to these things. It has definitely helped my belgian style beers to be able to pitch at a reasonably precise rate and control the temp with a probe into the wort and a fermentation chamber. If I was doing an IPA and I was fairly confident I had sufficient yeast then I wouldn't bother counting.
