Yeast is a fascinating life form that provides us mere humans with so many benefits to our health and social lives that it is worth exploring.
From its form to its function, and even to its reproductive abilities, for those of us in the brewing world, yeast is a never-ending subject of fascination.
What is yeast, anyway? How does it survive and thrive? How does it reproduce? Does yeast reproduce by budding?
All of those questions have interesting answers that only help us become even better contributors to delicious and delightful brews.
What Is Yeast?
Yeast is a single celled living organism.
It is eukaryotic in nature, which means it has its own enclosed nucleus.
And since its inception, millions of years ago, as a member of the fungus family, it has been in search of its two favorite foods: sugar and starch.
For millennia, it fed on ripe and rotting fruits and grains rich in sugary starches, needing only relative warmth, moisture, and its food source to survive.
Yeast is microscopic in size, but it takes up so much space that it fills virtually every environment, drifting through the air and settling on surfaces, even entering the human body as candida.
The yeast we most often think of belongs to a strain called Saccharomyces cerevisiae.
It is the yeast that ferments drinks and foods like beer, wine, and bread, though there are specific sub-strains that perform better for each.
A common misconception is that yeast cells do not reproduce during fermentation, that the cells simply die off due to the increase in alcohol.
While this can be true in the case of fortified beer and wine, a process wherein the brewer or vintner will add liquor to the beverage in order to stop fermentation and increase alcohol volume, in most cases, yeast not only does not die during fermentation, but in fact it increases in cell count!
Think about it – why would yeast be attracted to a food source that would ultimately kill it?
Instead, what happens during fermentation is that yeast consume the sugar and starch in the mixture, convert it to alcohol and carbon dioxide, and when that job is done, the yeast will lie dormant until it is given a new food source, at which point it will get right back to work, bubbling and frothing.
In fact, during racking of both beer and wine, the dormant yeast get agitated enough to get back to work seeking a food source, during which time the yeast will consume any yeast cell husks (from cells that have in fact died off) as well as any residual sediment that might create off flavors.
This is why so many brewers and vintners like to rack their beverages, to smooth out the edges on a fully fermented drink.
So, we know they won’t die off during fermentation, and that yeast will in fact reproduce, but… how?
As noted above, yeast is one of those miracle life forms, and as just one piece of evidence, yeast can reproduce both aerobically and anaerobically, with oxygen or without it.
Yeast can ferment in an airtight container with no access to oxygen.
However, it clearly prefers oxygen as anyone who has brewed beer or made wine can see from the vigorous frothing and bubbling that takes place in an open vessel.
Indeed, for many thousands of years, fermentation was always performed in an open vessel as that is how fermentation was discovered and perfect in the first place.
A vintner or brewer would prepare the juice (must) or grain water (wort), and then leave it exposed to the elements, at which point yeast would be attracted to the sugars and get right to work.
But industrialization had a big impact on changing this strategy as yeast was harvested, packaged, and sold, and many brewers and vintners grew wary of allowing in “wild yeasts,” forgetting entirely that at one point all yeast was wild and free to reproduce and ferment at will and even on demand.
Now, we seem to be returning to an awareness of this reality as we understand better the powerful function of yeast and how exactly it replicates.
Another wondrous fact about yeast is that it can reproduce either sexually or asexually.
Sexually, yeast apply a signaling pathway known as the mating factor pathway, wherein two parent cells undergo a process called meiosis.
Asexually, a single yeast cell undergoes mitosis, wherein the mother cell will create a smaller, daughter cell that is attached to the mother but grows and eventually separates. This process is called budding.
Asexual reproduction and budding are much more common in S. Cerevisiae, and are a common issue of concern for brewers and vintners, as understanding the budding process and how to count those cells is critical to assessing yeast concentration & viability accurately.
Note that the work of counting yeast cells including the budding daughter cells is very difficult as we are dealing with microscopic organism that can be challenging to differentiate from one another.
And getting it wrong could mean a huge difference in fermentation management and obtaining consistency.
The budding process is very similar to a human gestation in that, in the beginning, the bud is very small, but the energy required of the mother cell to keep that bud alive is enormous.
While the daughter cell is still less than 50% of the volume of the mother, it is considered weak and unlikely to survive on its own.
Once it has surpassed 50%, it can be considered a viable yeast cell that can and likely will ferment on its own.
Estimating the area of your budding cells just by looking at them under microscope is very much an error-prone process.
So your best bet in these technologically advanced days is to opt for automating your cell counts and have a user friendly, handheld device that will do that labor intensive lab work of yeast cell counting and viability measurements for you.
If you’re interested in finding out how you can use our technology to control fermentation and monitor your yeast (budding cells included), save work hours and improve the cost-efficiency of your business, drop us a line at [email protected] or check out the product pages (for beer or wine):
- Oculyze BB 2.0 (Better Brewing) Yeast Cell Counter App + Hardware
- Oculyze FW (Fermentation Wine) Yeast Cell Counter App + Hardware
Also, you can now get access to a fully functional demo account to test our Web App. Completely free of charge and with no commitment to purchase.