I have a packet of SafLager S-189 from Fermentis and I'm trying to figure out how many sells are in it. The packet is 11.5 gram and the expiration date is 04/2021 (which, I think, means it's 14 months old, as Fermentis gives their dry yeast a 36 months stated shelf life). Reading BeerSmith's guide: http://beersmith.com/blog/2011/01/10/yeast-starters-for-home-brewing-beer-part-2/ I see that they say that an 11.5 packet should contain about 200 Billion cells. However, looking at the product datasheet in the company's website: https://fermentis.com/wp-content/uploads/2018/08/SafLager-S-189_Rev1.pdf I see they only claim more than 6 Billion per gram, which only means more than 70 Billion for the entire packet. I'm guessing Fermentis's number is a minimum estimate, to make sure they deliver on their promises, but which is more realistic? What number can I comfortably assume here?

When I used to use dry yeast, 125 billion cells was a number that worked for me. The numbers out there are all over the place and usually state between 100 & 200 billion per pack.

Which number is realistic depends on your process: 70 billion is likely the number available to ferment if you sprinkle directly into your wort. Rehydration doubles the available amount (approximately). There are many factors, the age of the sachet.... The pitch calculator seems to handle pitch rates fairly well. Give it a go, it should tell you about how many cells are there and you don't have to be exact - pitch rates have a fairly wide tolerance.

I was looking for the right number to enter as cell density, which this calculator also wants. But I see that in this calculator it's said that 9 is a good estimate for S-189, so I guess I'll just use that number.

Your one packet will be good for 2 to 2.5 gallons of 1.050-1.055 lager fermented cool, but not at the lowest end of the range. I have good luck with 2 packets or S-23 or 34/70 in 5 gallons for a mid-gravity lager fermenting in the mid-50s temp range. The slurry from that is usually enough to do a 10-15 gallon batch of similar lager at similar temps as long as I use it pretty quickly. I've got some S-189 to try and I'm eager to see how it works.

Thanks, but that's not really what I asked. I know my one packet isn't enough, I want to make a starter to increase the number of cells, and to overbuild it, to use that for my next batch. I want numbers, so I could use the calculators, to know what I'm doing.

Bottom line is without cell counting, you're just guessing. The calculators enable a better guess. Put in the packet, its age and let the calculator tell you about what is in there. Hydration about doubles available cell count. Make a two-liter starter, that should be enough yeast for just about anything except a really big ale or lager. I trust the calculators and get pretty decent results.

I start assuming around Since you didn't mention what size batch you intend to make I just gave an example from which one could extrapolate. What you asked was the actual cell count and that, no one can tell you. Since I've had satisfactory results using the amount I mentioned, I assume a cell count derived from that. When I calculate pitch based on estimated cell count, I use at least 15 or so but I specifically ferment a little high on the first batch to build cell count without stressing the yeast. It gives me a big count in the slurry and works for my larger batches. If you intend to ferment cold, use a low number like you mentioned and build a monster sized pitch. Like Nosy just mentioned, it's just a guess. Estimates found online vary by 100% or more. You have to go on your own experience or take at face value anecdotal evidence offered by others and use that information to make a good guess. Good luck.

Sure, I will trust the calculators. The only thing is - the calculators want me to tell them the initial cell count. That's the info I'm trying to get. with the option that I found being: more than 6B per gram (Fermentis product sheet), 9B/g (Brewer's Friend calculator page) and 18 (BeerSmith's guide that I linked above). When you say "15" - you mean 15 Billion/gram? I'm definitely not asking for the actual cell count. I specifically asked what number can I comfortably assume. And of course I can go by my own experience, but I don't really have that much of it, which is why I'm trying to consult with some minds more experienced than myself.

The engineering solution would be to pick the least favorable count and work from there based on the fact that overpitching in most cases is less harmful than underpitching. If you want a "good" answer to this, you're going to have to buy a microscope and a hemocytometer and start counting cells. From the number of different answers we have given, you can assume there's no "right" answer so it becomes kind of like skiing: Pick a line and go. So in answer to the "comfortable assumption" question, pick the lowest feasible initial cell count and go from there, knowing you'll be wrong, but the least wrong.

Yes, I use a number around 15 billion. Some estimates are as high as 20 billion and some less than 10. To reiterate, my pitch is specific to my fermentation temp and schedule and I'm usually using a first batch to build slurry for a bigger batch. If you're intending to do a very slow, low temp fermentation on the first pitch you have to take that into consideration. And you can't leave out good aeration, pure O2 much preferred. As for what number you can comfortably assume, you sort of have to figure out your own comfort level. I hope I've been able to relay my experience in a way that's helpful to you. If this is your first lager, you may be overthinking it. If you've already brewed some lagers and are just trying a new yeast use the methodology you're used to and evaluate the results. Either way, save the slurry. Subsequent generations are invariably better than the first pitch as long as you keep things really clean. Good luck with it.