Imagine for a moment that you are not an evolutionarily tuned great ape, with dazzling cognitive powers and the foundation of all human civilization beneath your feet, but rather a simpler, more purposeful organism. Imagine you are a single cell of Saccharomyces cerevisiae, newly roused from your dormancy and afloat in a sugar- and nutrient-rich soup cooked up especially for you.
At first, you’re sluggish and weak. Yet you are driven by a biological imperative to which even the greatest apes are sympathetic, and you seek what your cell requires to grow stronger. Vitamins, minerals, and oxygen are crucial, and you feed voraciously, yet still the pounding drum of biology reverberates through your being. Survival is not enough, and you begin to change. A lump forms on your cell membrane. This bud swells and grows, filling with cytoplasm until your very core splits in two. A chunk of your cell’s nucleus migrates to the bud, carrying a copy of your genetics with it. Soon your bud has grown to match your own cell in size, and this daughter cell detaches, taking your DNA with her into the future.
Meanwhile, your mothers and sisters teeming around you in the billions feast and bud as well, churning the medium with gaseous excretions and clumping together in ad hoc colonies. Brewers call it high kräusen—but yeast, if they had a language of their own, would call it one hell of a party. The biomass of yeast in the tank explodes logarithmically, doubling the number of cells every few hours as the sugars in the medium are consumed. What was once sterile wort is transformed into beer, as the monocellular population produces ethanol, carbon dioxide, and a virtually uncountable catalog of flavor compounds.
Costs and Risks of In-House Propagation
Yeast are one of the four principal ingredients in beer, but they are also a by-product of the brewing process. Yeast make more—a lot more—yeast with every batch of beer, while a lab can shepherd just a single cell of brewer’s yeast into a thriving colony of organisms eager to go to work on sugary wort. Most commercial brewers (and many homebrewers) take advantage of the surfeit of viable cells produced during fermentation by repitching yeast from a finished batch into their next brew, and there are specialized tools and processes for wrangling yeast from batch to batch.
On paper, brewers should never need to buy yeast—they make more than enough. Yet there are enough exceptions, challenges, and realities in a commercial brewery that most still buy pitches from yeast suppliers. The theoretically perfect scenarios for limitless yeast reuse break down in a few main ways:
- First, when yeast reproduce during vigorous fermentation, they are not always creating perfect copies of themselves. Mutations are a real force when dealing with populations of organisms measured in the thousands of billions.
- Imperfect environments—such as a cylindroconical tank, even when well-managed—stress the cells and drive further genetic drift.
- Common yeast-harvesting methods exacerbate changes to the original culture.
- Vagaries of production scheduling often take precedence over the yeast’s preferred timetable, and storing yeast while maintaining their viability and vitality is tricky.
So, just because a brewery can reduce its reliance on external yeast supplies, and thus save a few bucks, doesn’t mean that’s always the best decision from a business standpoint. Many brewers, yeast suppliers, and lab technicians agree that focusing on growing-up yeast cultures isn’t always worth a brewery’s time and labor.
At the scale of most craft breweries, pitches are a reasonable expense. Meanwhile, simple processes can reduce the batch costs of yeast without dedicating staff and real estate to propagating enough yeast for every batch.
“Self-propagating yeast will not save you money until the scale makes sense,” says Chris White, founder of White Labs. Beyond the labor and facilities costs, “yeast doesn’t grow in water,” he says, and spending time and money on making yeast-growth medium instead of wort that will become salable beer adds up.
About 10,000 barrels of annual production seems to be the breakpoint where in-house propagation starts to make sense. Plus, most off-the-shelf yeast propagation systems from the big equipment manufacturers such as GEA and Alfa Laval are sized for much larger breweries and priced to match, stretching into six or seven figures.
However, yeast-propagation systems are not the critical equipment at the craft brewer’s scale, anyway. The most important piece of gear for good yeast handling in the brewery is an in-house lab. “Good practices are cheaper than equipment,” White says, “and a lab gives you visibility into the [brewing] process.”
The space and equipment needs of a lab are not as stringent or expansive as one might think. A microscope with accessories is the critical component, alongside an easily cleaned workspace separate from the production floor. The costs are minor compared to brewhouse components, fermentation vessels, or packaging equipment. Staff trained to perform the required tests and procedures is another requirement, but you don’t need a PhD to do the work.
“This is microbiology 101 stuff,” says Nick Impellitteri, founder The Yeast Bay, a boutique supplier based in Portland, Oregon. A microbiology textbook was once an obligatory part of a brewer’s library, but today’s reference library is just a Google search away, right there in our pockets. However, even with a lab and someone to run it, a brewery may not want to deal with in-house propagation.
“In-house prop needs to support the brewery’s business model and product philosophy,” says Victor Novak, director of innovation at Figueroa Mountain in Buellton, California. It’s harder for breweries making lots of one-off brews to take advantage of in-house propagation, and growing up pitches adds more complexity to production schedules that are already complicated.
“Sometimes ordering a pitch solves problems,” Novak says, “and brewers love to solve problems.”
Real World Wrangling
I have no hard data to support this, but anecdotal info and commonsense extrapolation would suggest that most batches of beer brewed in the United States are made neither with purchased pitches nor with pitches propagated in-house on specialized equipment. The most common method for inoculating a batch of wort at smaller breweries is the “cone-to-cone” pitch—a technique that blurs the line between buying a one-and-done pitch from a supplier and using a homegrown culture.
As we’ve established, yeast have no real interest in making beer—they are all about replication. Brewing is largely about controlling the environment in which yeast grow, and beer is the by-product of all that replication. Of course, this leaves brewers with a lot more yeast than they started with, all conveniently collected in the cone at the bottom of the fermentation vessel. All it takes to get another batch going is some hose, a pump, and another fermentor. Move the yeast slurry from the finished beer to another vessel with fresh wort, and another fermentation begins. The upsides are obvious: almost no added cost per batch, no specialized equipment necessary, and many brewers report reusing the “same” yeast for 10 or more batches.
Of course, the cone-to-cone technique requires a compatible brewing schedule, synchronizing the completion of fermentation with the production of fresh wort. There is also the inherent opacity of a closed transfer; while there’s less risk of contamination, there’s also no visibility into what you’re actually transferring from that cone. How many cells of yeast are in each milliliter of slurry? How viable and vital are those cells? Has there been any notable genetic drift in the strain—or, worse, is there microbial contamination of some sort? Flow meters are of little help because the compacted slurry varies in density from fluffy to firm, complicating the calculations. After repitching that yeast culture into the same wort recipe enough times, a brewer can collect data and watch for trends and anomalies. However, those nagging variables are an enemy to consistency.
Enter the yeast brink, a simple bit of kit that solves many of the problems with cone-to-cone transfers. A brink is really any vessel used to store yeast, be it a plastic jug from the yeast supplier or a stainless-steel vessel dedicated to the task. A modified half-barrel beer keg, either custom-built or purchased from suppliers such as GW Kent, is a common solution to the yeast-storage problem.
Brewers can transfer slurry from a finished fermentation into the brink and weigh it—either with a keg on a scale, or a larger vessel installed on load cells—then the lab can check the concentration, viability, and vitality of the slurry before it’s used in another batch. It’s best to use this brinked yeast promptly, but if stored cold, the yeast should remain viable for a few days or a week.
Yeast brinks are a common tool at craft breweries, even when they’re not a regular part of production. However, using one without lab support to understand the health of the yeast going into and coming out of a brink is asking for trouble. It may be less risky for smaller brewpubs that sell all their production over their own bar, but once packaging and distribution come into the picture, small risks can grow into costly repercussions.
“Spend money on microscopes, pipettes, and staff, and you won’t have to spend money on recalling a batch of contaminated beer,” Impellitteri says.
All Growed Up
It’s surprisingly rare to find a craft brewery propagating yeast from single colonies up to full-sized commercial pitches. Large regional breweries such as Sierra Nevada and New Belgium have cutting-edge propagation systems to keep their house cultures healthy and abundant. Automated, batch-fed yeast reactors are dazzling machines, but they are out of reach for all but the biggest producers.
The more pedestrian propagation that happens in craft breweries is the “two-turn grow-up.” This method reduces the size of the required pitch by using yeast’s explosive growth to the brewer’s advantage. It works best when a fermentor is a bit more than twice the size of a batch of wort. The brewer half-fills the fermentor with one turn of the brewhouse, pitching the proper amount of yeast for that amount of wort. Overnight, the yeast grow enough to ferment twice that volume, and the brewer tops it off with a second batch. At that point, the yeast are energized by their first feeding and ready to vigorously ferment the whole tank.
One brewery that actually has the setup to propagate full pitches from slants—those test tube–like vessels for storing yeast cultures—is Old Nation in Williamston, Michigan. Old Nation brews about 18,000 barrels of beer a year and can grow a slant into a pitch big enough for its 40-barrel brewhouse. Still, even with a particular focus on in-house propagation and yeast management, Old Nation starts with a purchased pitch.
“It’s easier to buy a liter or two of yeast and grow that up, and it’s faster,” says Old Nation cofounder Travis Fritts. He says his lab techs are busy enough without doing 200-milliliter fermentations. They do use a dedicated yeast-propagation tank, however—a custom converted, 10-barrel conical fermentor equipped with a long-shaft internal impeller, oxygen injection, and load cells to accurately measure yeast quantities. They produce a special wort meant for the propagator’s growth medium. All-malt and about 11.5°P (1.046), the wort is loaded with yeast nutrients and enough hops for “8 or 9” IBUs—a level that Fritts calls “old brewer’s voodoo.”
“It’s supposed to condition the yeast to the presence of hops,” he says. “Maybe it’s nothing, but we’ve always done it.” He adds: “None of this is hard.”
For Fritts, there’s no meaningful difference between making a starter in a one-liter flask and making one in a 10-barrel tank. Meanwhile, in-house propagation provides a greater connection with the yeast as well as with longstanding brewing traditions.
Fungal Husbandry
To yeast, beer is just a by-product of its biology. But to brewers, yeast are both a crucial component and a part of a brewery’s waste stream. From the first recipe development steps to the final quality control of the finished product, yeast are integral to the brewing process.
The best brewers tend to be those who are “microbially minded,” keeping yeast health in mind with every task they perform in the brewery. The modern brewery is dense with equipment and towering vessels, a complex network of piping and hoses, an intricate machine as finely tuned as any industrial plant—but the machines doing the work of fermentation are tiny. Uncountable billions of individual organisms toil under the brewer’s watchful eye (or the lab tech’s microscope)—and what are brewers, really, but shepherds for this flock of single cells? Each strain has its own preferences, and each fermentation vessel is a different pasture for their feeding.
Shepherds love their flocks, and brewers need to love, respect, and understand their yeast, to take care with each step—from propagation to pitching to harvesting.
“Yeast is the soul of beer,” says Novak at Figueroa Mountain, “and you have to understand every aspect of yeast to make truly great beer.”