Maintaining A Healthy Yeast Bank Long Term

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One of the most important things you can do to brew great beer is ensure you have a healthy, unstressed yeast population. From pitching rates, fermentation temperature, avoiding contamination by competitive organisms, all the way through bottle conditioning; an unhappy yeast culture will kill a batch faster than you can drop a 5 gallon glass carboy on a concrete patio.
As long as your clean, you can do prepare your yeast for storage outside of a lab.
The best way to ensure you have the happiest yeast possible is to completely control the cold-chain of your yeast supply. By that I mean yeast ranching, and doing it the right way to ensure you have a real, pitchable amount on brew day. Add in the ability to archive rare strains, as well as save you a few bucks per batch, and you’re now wondering “why haven’t I done this sooner?” You don’t have to own a certified lab to do this either (ie, my “laboratory”, an unfinished plywood tabletop in a storage room). All you need is a little patience and a penchant for cleanliness and detail.
Table 1: Overview comparing 3 different yeast banking techniques
The table outlines some of the various advantages and disadvantages of each type of storage outlined in this article. Generally, there are 2 ways to keep a yeast bank: at 4°C or at -20°C. Refrigerator temperatures are good for short term storage, but true banking will require a freezer stock to essentially halt biological activity. Since yeast cell walls will rupture due to the formation of ice crystals at freezer temperatures, you’ll need to add a cryo-protectant to reduce the crystal formation. We’ll go into that later. First, the easy way.

Storing Under Beer


Keeping yeast under beer is effective if you have a fast turnaround
Let’s say you brew a beer using a sachet or liquid pack of yeast from the homebrew store. At the end of primary fermentation, you’re left with a boat load of cells (usually around 2 trillion in a 5 gallon batch) in a cake after racking. Using this trub is the easiest way to keep a fresh stock of a favorite yeast strain. Fresh is the key word here. Yeast will continue to metabolize and be otherwise fairly biologically active in any environment above -20°C, so the term “fresh” is time dependent. A good rule of thumb is to store yeast in the fridge under beer no longer than 2 months before taking a portion of it and making a new starter to restart the clock.
Method
Take the cake, swirl it around in the bucket or carboy in the little beer left at the bottom to re-suspend, and pour into mason jars sanitized with your favorite solution. Keep the caps loosened for a few days and store them in the refrigerator. If used within a couple of weeks, 50ml of this compacted slurry at the bottom of the jar is good enough to inoculate a new 5 gallon batch. Viability will be reduced, and sluggishness will increase with time, so take that into consideration or use one of many online calculators (MrMalty, BrewersFriend, etc) to estimate the volume to use.
Notes
This is a very quick and dirty method for maintaining a yeast bank. While being quite easy and well suited for brewing many beers back-to-back with the same strain, it will quickly become difficult to maintain many strains or keep mutations to a minimum. That being said, there are also some requirements to keep yeast cultures this way. The batch used to create the initial cake must be very low impact to the yeast. It should be low gravity, reasonably low temperature (no hot and fast ferments), must be free from bacterial and wild yeast contamination, and it must not be a blend of strains that are used in many commercially available cultures. Also, it seems as if there has been a shift in the opinion in “water washing” the yeast prior to storage in a jar. Though logic suggests that a yeast population absent of hop debris and coagulated proteins would be beneficial for storage, the general thinking these days is that more collection steps would only increase the possibility of infection. I agree with this argument, and I suggest just dumping the whole lot into a sanitized jar for collection. K.I.S.S., always a good mantra in brewing.

Agar Plates and Slants


Keeping yeast in slants is more viable, but will require you to build up a healthy starter.
A better way, though fairly more involved, of keep a yeast bank is through agar gel slants and plates. This is the method of choice for microbiologists for keeping viable strains actively growing, so why not for us homebrewers? Once you have this method down, it opens up a whole new powerful set of possibilities. Some examples include culturing wild yeast from your backyard or garden, removing bacterial contamination from a rare strain, and selecting a high growth or high alcohol tolerant strain.
Method
There are as many ways out there to accomplish agar slanting as there are styles of brew, so I will very roughly walk through the general procedure. Google “agar slants” and a multitude of great articles will come up outlining the details. There is a general list of equipment needed for agar slanting: agar powder, pressure cooker, petri dishes or small vials, stainless wire or inoculating loop, and mason jars. Ok, so not a long list, and certainly doable without a large budget. The general steps are fairly straightforward:
  1. Prepare a 2% (2g in 100ml wort) agar solution and pressure cook for 10 minutes in a jar
  2. Allow the agar to cool to around 70°C, and pour 10ml into each 100mm petri dish, or fill the vial halfway, and keep at a slant (“agar slants”, get it?) while the agar gels.
  3. Allow the dishes and vials to cool.
  4. Take the sterilized stainless wire or inoculating loop and dip a sample into the smackpack or yeast vial and spread on the surface of the agar gel
  5. Cover and allow the yeast to grow into a nice thick layer on the gel at room temperature
  6. Seal the plates or screw the lid of the vials and keep at 4°C
Since the culture has not been through a true growth phase in the stress of making a normal beer, you can keep reculturing these plates without too much worry about mutations, as opposed to keeping jars of slurry noted above. The plates can be kept in the fridge for 6 months to a year before having to replate, and replating is as easy as taking the inoculating loop and smearing a sample from the old plate into a new one and repeating the growth/storage process. To grow a starter from the plate, take the sterilized loop and scoop a sample from the slant, twist it around in 2-5 ml of wort. Grow the wort for a couple of days, and incrementally build that volume into your target starter volume, not exceeding a 1:10 dilution (for example, take the 5ml starter, dump it into a 50ml starter and grow, and dump that into a 500ml starter, etc).
Notes
Without describing every single detail along the way, use common sense in preparing the cultures. If you're using glass petri dishes and vials, sterilize them in the pressure cooker. If using plastic, make sure you buy pre-sterilized packs, keep them sealed, and don’t reuse them. Beyond just keeping a master stock of yeast, this method can be used to clean up a contaminated culture by smearing a sample of the batch, and picking and growing individual colonies of yeast from a single cell. The yeast are white, foamy looking, while bacteria are usually shiny. Mold is obvious, and the whole plate should be thrown out if seen, as the hyphae underneath the gel will no doubt pop up somewhere else.

Frozen Stocks


I am a microbiologist by education and trade, and in my opinion, keeping frozen stocks of yeast cultures is the way to go for a homebrewer (and also quite simple to do). While you don’t get that warm, fuzzy feeling of watching a single cell grow into a colony and knowing exactly how pure your culture is, with careful aseptic technique you can keep dozens of strains ready to go for pitching in a couple of days, and it doesn’t take a lot of maintenance or equipment (or valuable refrigerated space). The addition of a cryopreservative (food grade glycerin) is required as mentioned above to keep ice crystals from rupturing the cells, but everything else is pretty much the same as keeping slurry jars. An added benefit of storing cells at such a low temperature is that biological activity slows way down, essentially halting the chance of spontaneous mutations that may occur from fridge temperatures.
You can store a lot of yeast for a lot of time if you're able to freeze your cultures effectively.
Method
My method for keeping frozen stocks of yeast is focused on creating single-pitch tubes to make fresh starters for 5 gallon batches. You can also make much smaller tubes to steal a small quantity without thawing the stock and step the culture up for a starter. That takes more time, and time is valuable, so I don’t do it, but it is perfectly viable. The equipment needed for frozen banking is simple: pressure cooker, mason jars, sterile tubes, and glycerin (drug store).
  1. Make a 25% v/v stock solution of glycerin in water (30ml glycerin, 70ml water) and pressure cook for 10 minutes.
  2. Make a 1000ml starter from a fresh yeast culture and allow to settle or cold crash in the fridge
  3. Decant the beer off the top and swirl the yeast up
  4. Divide the yeast into 10 vials
  5. Double the volume of each vial using the cooled 25% glycerin solution (for example, after decanting you are left with 50ml of yeast slurry. Add 5 ml slurry to each vial and add 5ml 25% glycerin to each vial. This will give you a final concentration of 12.5% glycerin).
  6. Mix the tubes well and place in a container filled with isopropyl alcohol to the liquid level in the tubes to reduce the freezing rate in the freezer (this can be skipped, but cell viability will be reduced if placed directly into the freezer. Cells prefer to freeze at a rate of 1°C per minute).
  7. After 24 hours the frozen tubes can be removed from the alcohol and stored for several years.
  8. To inoculate a 1000ml starter for a brew, quickly unfreeze the tube to the starter wort temperature and dump it in. That will create a 1:10 dilution from the earlier split. Using a stir plate will have the starter ready and settled usually within 48 hours.
  9. Once you are down to one tube in the freezer, make a starter as in Step 8 using the tube, and freeze into more tubes as in Step 3. So you theoretically from one smack pack and some DME have made enough cells for almost 30 batches in just 3 controlled generations of culture (or over 700 batches if you expanded each tube out 3 generations).
Notes
If you increase the final concentration of glycerin in the frozen culture to around 50%, viability will be reduced, but the cells will not freeze solid, and you can dip a sterilized loop in there to inoculate a small starter, very much like inoculating from a slant. This way you can cut down the storage volume of your stocks to a few 1.5ml tubes instead of larger vials. But keep in mind it takes a week or more to grow a starter from that instead of a couple of days.
Regarding the storage time, it is also assumed that a chest freezer or manual defrost freezer is used. If a fridge/freezer is used that has an automatic defrost cycle, the tubes should be placed in a styrofoam box with ice packs inside to maintain temperature while the defrost cycle works.
Keep Records
Whichever method you choose to maintain your yeast bank, keeping detailed records is mandatory. Typical details are yeast ID, strain, source, date commercially manufactured, storage date, number of generations from packaging, parameters of beer obtained from (if slurry), date to re-plate or refreeze, among others. These records will be the living document that tells you how viable the stocks may be, when routine culturing is necessary, and depending on how detailed you get, how changes in your protocol can increase cell viability. These are all good things, and just as necessary as keeping a brewing log book to note how a beer turned out. If you’re a yeast freak like myself and eventually build up a stock of over 40 different strains, you’ll definitely need a spreadsheet with tasting notes, fermentation parameters, and ideal beer styles in order to plan your next brew.

A Final Note


Yeast are incredibly resilient little buggers. Just a few years ago a professor at California Polytechnic State brewed beer with a yeast strain found to be 45 million years old that was stuck in a chunk of amber, inside the digestive tract of a bee. That’s one tough cookie of a cell that’s been through a lot over the millennia. In contrast, the methods given above are aimed at reducing exactly this kind of stress, but are by no means set in stone or an all-inclusive list. Variations in almost every step will likely give great results. Keep in mind the few critical rules: reduce contamination, reduce stress and mutations, and control the growth cycle. No special tools are required to keep a healthy yeast bank long-term; use some common sense, the guidelines above, and you’ll have a yeast population ready for any brew you can throw at them.
 
Well done! I enjoyed this intro to managing your own Yeastie Boys! I've done very little of this because I have a sporadic brew "schedule". This may be intriguing enough to get me into lab geek mode :0) Thanks for the article.
 
I have been doing the mason jar method stored in the fridge, but haven't brewed probably since mid Dec. (unheated garage, just too damn cold here in the winter).
Some of the yeast I have is probably 6 months old. Are you saying that it is probably unusable? I always do a starter with it in any case. Will that be enough to bring it back from the dead, or should I just go get new? What kind of mutations does it do?
I don't rinse my yeast, I just leave about an inch of beer on top of the trub in the carboy, swirl it around, and dispense into sanitized mason jars, and then store in the fridge.
Getting the point where it is warm enough in the garage to brew again, so just wondering if I should go get new, or if these will be fine. Pretty sure I have used some of them 4-5 months later from collecting. Some may be older than that however.
 
Do you have a method of sterilizing you would suggest for those without a pressure cooker? Or is it truly a must have for the methods above that use it?
 
The timelines listed in the table are pretty conservative, and are more along the lines of establishing a schedule for maintaining your yeast stock. That yeast under beer in the fridge will more than likely be perfectly fine for a new starter after 6 months. I've made a starter from a jar that was a year old for a successful brew, so it can easily be done. The caveat is that you don't know exactly what changes have occurred in that jar over time. Bacterial growth, changes in yeast metabolism or conversion of sugars, etc.
Mutations are completely random in these cases, and can't really be defined. But I can tell you they happen. I did a scotch ale with a culture that had a rough freezing life (thawed, refrozen...ugh, freezer problems) and made a good starter, smelled and tasted ok, so I used it. The beer had a twang that was unlike an infection, and no significant amount of bacteria was present under the scope. I chalked it up to possible genetic changes and it became my first dumped batch over 10 years of brewing.
Bottom line, I bet they're fine. Smell the jar, taste the beer on top, and make a starter repeating the evaluation. Good luck!
 
good article, yes. I've been propagating yeast from the original package and storing in the frig. How the heck do I get temperatures as low as 20 below zero at home?
 
Some may argue with me - but thats ok... I just made a batch of hefe where the slurry sat at 40f from August to February. I pitched it, no starter, and it kicked off within 24 hours. The finished product tasted great and that's about the 4th time I've pitched that yeast - originally WB-06. I was a little worried about it being 5+ months old, but it turned out fine. I may open another package of WB-06 for the next batch of hef though. Ya never know when pitching old slurry will bite ya.
If you're worried about your slurry, replace it. Otherwise, rdwhahb....
 
For the frozen stocks of yeast, what size tubes do you use and what is the volume of the yeast/water/glycerin mixture in the tube? You mentioned 5ml of yeast and 5ml of solution, but I am confused as you later say to add that to a 1000ml starter for a 10:1 ratio. Can you explain?
 
Great article. Thank you. I noticed the word "microscope" was not mentioned. If I understood any of this, a microscope could/would/should be used for slants, but not for frozen stock?
 
Nice article. I've been doing slants and plates for a while now, but your method of freezing seems easier. Definitely the easiest explanation I've read thus far. What tubes do you prefer?
 
It's not a must have, but it's nice to have that extra bit of insurance. StarSan works surprisingly well, but the autoclave has the benefit of sterilizing any wort you would use to grow starters and such, better than boiling. You can also heat sterilize the glassware only for an hour at 350F in the oven. Just be sure to let it cool in the oven, don't temp shock it.
 
Sure, the volumes going into the tubes are 5ml of concentrated slurry and 5 ml of 25% glycerin (the tubes are 15ml conical plastic tubes). To get the slurry concentrated, the 1000ml starter is cold crashed and decanted so that there is 50ml of yeast and beer remaining. That 50ml is swirled around and split into 10 tubes, 5ml each. Then 5 ml of the glycerin stock is added on top. When you thaw that tube, which was 10% of the total cells from the first starter, dump it into a new 1000ml starter, and you got a 1:10 dilution.
 
I use these size tubes:
http://www.amazon.com/Globe-Scientific-6285-Polypropylene-Centrifuge/dp/B003T3V7VG/ref=sr_1_9?ie=UTF8&qid=1460465850&sr=8-9&keywords=15ml+conical
But any kind will do, just make sure they are sterile; if it doesn't say, assume they are not.
 
Thanks! All this information is out in the HBT space, but hopefully this condenses it a bit to make it easier for folks to start ranching.
 
Very timely article since just last night I was thinking I needed to take better care of my yeast. Seems that by going the freezer route I can even reduce my footprint - my wife is not happy at all the mason jars in the fridge. lol
 
Any kind of alcohol would be fine, you could use some cheap vodka in a pinch. I've done the tubes straight into the freezer and the cells noticeably took a hit, the starters had a couple day lag time. You can also put the tubes in a styrofoam box in the freezer, and it has the same effect, slowing the chill rate. It just temporarily takes more space in the freezer.
 
You don't have to use a microscope for any of it, I guess that's why I left it out. Microscopes are fun, and to a point are useful in qualitatively measuring bacterial contamination in the brew (with good optics), but not necessary. For slants and plates, the colony from a single cell will be obvious and perfectly round, maybe 2-3mm in diameter, so your eyes are good enough. Any bacteria or mold will be clear as well. Frozen stock quality will rely on the cleanliness of your procedure, but a scope could tell you if bacteria is present in the starter. It comes down to how serious ($$) you want to get. That said, I have a scope, and I use it for these reasons.
 
Can you please help me understand “Make a 25% v/v stock solution of glycerin in water (30ml glycerin, 70ml water)?” v/v means volume in volume so wouldn’t 30ml glycerin, 70ml water be a 30% v/v solution?
 
Thanks for putting this together! Is much appreciated to have an educated and trained expert contribute hobby level relevant articles in such detail. Perfect amount of detail!
I would love to hear what your opinion is about determining viability and yeast count from such a yeast bank (Frozen Stock) after revival and starter propagation. I've thought about getting a hemacytometer and USB "microscope" to test. I probably got some of those terms wrong there, but its been awhile since I thought about this. Couple of questions if you don't mind.
How important is working in a negative pressure (or under a hood) for yeast work?
Do you think doing viability and cell counting is worthwhile for the time invested when using these methods, and are you doing this for brewing at home?
I'm a collector kind of person. I'd LOVE to have a huge yeast lab. I HATE when I want to brew but cannot find a suitable yeast (such as Pacman, or other seasonal strain) and end up improvising. My life, like many is consumed by work, children, family, and multiple commitments from these. Brewing is a hobby that is relentlessly stranded on the back burner, at least for me. Adding time to the process isn't a good thing, but I will say adding money, say for example buying mail order overnight shipped yeast for a lager beer for a ten gallon high gravity double bock brew in the middle of the summer in Florida, is ridiculously expensive. I despise spending money on yeast. I am looking forward to using some of your methods to expand my yeast library.
Do you have any thoughts about freeze drying yeast? I saw an ad for a thing called the harvest right or something like that, which is a home freeze drying appliance. I've been contemplating buying it and was wondering if it would work for yeast too.
TD
 
Great article. Thank you.
I've been washing and reusing yeast for awhile mainly because I'm cheap. But I'm interested in the freezer method. In step 8 of the freezer method you say "quickly unfreeze the tube to the starter temp" how would you recommend doing that? Is it just by simply taking it out and letting it thaw? And you sourced 15ml tubes for freezing. Are you adding 10ml and leaving 5ml for expansion? Thanks again!
 
Great article, gonna try this weekend. But Am just curious if you get enough cells from method 3? According to mr malty counts: http://www.mrmalty.com/pitching.php
- say you have a white labs veil with 180billion cells (per latest white lab numbers). 1 l starter will make around 1.5x more, meaning you have around 270b cells. you split them in 10 veils, 27b each and make 2l starter from one of those you frose, making 2x more cells. so you have around 54b cells from that starter that you pitch, which is 4 times less than you should under normal conditions. The counting is done with nearly idal conditions, you most likely end up with some less cells. Or did I miss something?
 
Yep, thanks. Typo there, 25% would be 25ml glycerin and 75ml water. Truth be told, anywhere from 10%-20% final glycerin concentration would give pretty similar results.
 
Excellent write-up, easy to follow, I will definitely freeze some cultures now, but one question.
Why not just glycerin and freeze straight from the smack pack or WL vial?
Looking at 1 month old liquid yeast you would have 80 billion cells in 125 mL (Wyeast example). You could fill 10 vials at 8 billion cells a piece with 12.5 mL of yeast and 12.5 mL of glycerin.
For the same 1 month old liquid yeast, your method suggest inoculating at a rate of 80 mil/mL yielding a growth rate of about 1.75. You would end up with about 140 billion cells and depending on density about 100 mL of slurry. Divided into 10 individual vials you would have 14 billion cells in 10 mL of slurry, not much different from the above method, or straight from the pack.
Using the above example for 1 month old yeast, either method, 1 vial into 1 L would lead to an inoculation rate of about 10 mil/mL and a resulting growth rate of about 4. Ending cell count would be 40 billion, not enough to brew a typical beer over 1 gallon. It also seems that a multi step starter would be required when growing from 10 billion to 100 to 200+ billion cells.
At growth rates 2-3 i.e. inoculation rates 25-50 mil/mL, pitching 1 thawed frozen vial by the example above would grow from 10 billion to 30 bil. via a 400 mL starter, stepped to 90 bil. via 1500 mL starter and finally 180 bil. via 1800 mL starter. Respective growth rates 3, 3 and 2.
This is my understanding, do you have any input or insight for me/us?
 
Negative or positive pressure is definitely not needed for doing this work, though access to that would significantly decrease the chance of any contamination. Positive pressure would be pretty easy, just put a high efficiency filter in front of a box fan blowing down into a plexiglass box with one side open to work in. But if you're careful to not keep any liquids uncovered for any long amount of time, that's usually good enough.
Viability is fun to do to get really accurate counts at stages of growth, but as I saw, if you standardize your procedure well, you'll get the same counts time after time, then it's just sort of a waste of time. So I did do it for a while to understand the max densities and growth rates of different strains (which vary widely, take the calculators with a grain of salt). Your terminology is correct though, you only need a hemacytometer and decent 400x total magnificantion. There are a few threads looking at cheap scopes on HBT.
I doubt the home freeze drying machine would work, but if you try it, report back! Active dried yeast is a fairly controlled dehydration process, more than simply freeze drying. Dried yeast are protected somewhat granularly by debris that retains the inner cells...you know, I'll be the first to say I don't know enough about it to even discuss. I will say I traded yeast with some folks on here by taking a drop and letting it dry on paper, wrapping it up and sending it by letter. Viability is shot to hell, but with a plate, you can select strong colonies. So maybe the freeze drier would work....
 
I think the problem is making the 2L starter from 27B cells only gets 2x more. Let me give an example of what I typically find for cell counts in my starters on a stir plate.
Start with 100-150B cells in a smackpack or vial, add to 1L starter, and you might get 1.5x, maybe less. I find that an average max density of my stirred starters is around 200 million viable cells/ml. So that 1L now has 200B cells. Split that into 10 tubes, 20B each. Take that 20B tube, and add it to a 2L starter and grow. The final density doesn't change with a 1:20 dilution and similar OG, conditions, etc. It will usually still be 200 million/ml. So your 2L starter now has 400B cells. I think in terms of final densities given standard starters, as that is what is important. If you make them happy, they will keep giving you that max density.
 
Yep, I put it into a cup of slightly warm water, and try to thaw it as fast as possible without a lot of heat. Just swirl it, etc, and try to get it to roughly the same temp as the starter as not to shock it. Yeah, the extra 5 ml is for expansion, or if I didn't eyeball the volume of the decant good enough, and all the tubes have 6ml instead of 5ml, so 12ml total with the glycerin.
 
1) Totally, you could definitely just freeze the smackpack or WL vial to a final 12% glycerin and be done. The starter just ensures they were viable to begin with.
2) It's totally possible to grow a 10million/ml inoculation rate in a 1L starter into 200B cells. Every strain is different, and has different final density preferences, some 250million/ml and some 90 million/ml, all assuming the same gravity wort, because cell number is determined to a point by grams of extract, not starter size. These are ideal conditions though, with a stirplate and good oxygenation, healthy starter population. But it's typically what I see. Where did you get the growth rate of 4, as a multiple? If the growth rate is a population doubling, then 10B->20B->40B->80B->160B (4 generations). If you use this calculator (http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/), it's pretty close to what I usually see, but more of an average. I see 50% more or less than those final cell counts depending on the strain.
This is very much a YMMV sort of situation, and depends greatly on who is working with the cells, type of extract, temp, stirplate, etc differences. I don't do stepped starters because I saw that I didn't need them, unless I am doing a gigantic high gravity lager. a 1L or 2L is all I need for 5gal batches (disregarding barleywines). I think the key is keeping the inoculation rate above 10M/ml in a standard starter, any lower and they tend to take a hit.
 
Jamil and Chris Whites yeast book.
Extracted and posted here:
http://beersmith.com/blog/2011/01/10/yeast-starters-for-home-brewing-beer-part-2/
 
They also suggest inoculation rates of 50-70 mil/mL as ideal. But empirical and "what works for us" are two different subjects.
 
Agreed, we're not commercial, and it's very hard to standardize one rule of thumb for all strains, for all beers. Even so, I generally go with the standard commercial pitching rule of 0.75M/ml/deg plato for an ale and 1.5M/ml/deg plato for lagers (that's 10-20mil/ml for a 1.050 beer. That would be an inoculation of 9B cells in a 1000L starter for an 1.050 ale or 18B for the same lager (matching inculation rates for the beer, gets them used to that growth cycle).
Again, I wrote this all around doing your own ranching, not using smack packs into a starter, which the BeerSmith link refers to. In those cases, yeah a growth rate of 1-2 is all you'll likely see. The inoculation rates that I use are more like making a batch of beer, which results in a heck of a lot more healthy cells than 4x. My problem with the link is the statement that "No matter how large a single starter is we are not going to get a growth factor greater than 6.0." That's just too general, and misleading. He also at the end suggests that for a 1.050 ale, 80B cells from a smack pack will be needed to add to a 3.5L starter to get 177B cells. Does anyone making a lager use 2 smackpacks in 7L? The method I show here will get you 200B+ cells in a 1L starter, with 9 more just like it from one smackpack. Ridiculously sized starters just empirically are not necessary to get commercial grade pitching rates. Again, this is for ranching your own cultures, not starting from (and paying for) smack packs, and maybe that's the difference that I should have added to the article.
Thanks for the discussion; these are heated topics, and always lead to some disagreement! The important thing is that people, who want to, understand how these numbers are calculated, and some data from homebrewers like us to confirm these calculators should always be part of the discussion.
 
These look like great instructions. I'm interested in the freezing method and have a few questions:
1. What should I look for in a pressure cooker? I will need to buy one, but I would like to also use it for canning, cooking, and kitchen use. The electric ones look nice, but seem like they are not useful for much else.
2. If I get a larger size for general kitchen use, when making the glycerin solution, can I sterilize it in a smaller flask inside the pressure cooker? I would think it would be less wasteful than making a larger batch of it.
Thanks again for the write up, this method seems practical and achievable now.
 
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