Yeast Cell Count During Fermentation

Yeast cell count during fermentation is essential to continued success of your fermentation in future batches, particularly if you are working with the same yeast. Just like we take gravity readings throughout the brewing or winemaking processes, so too we much constantly check the viability of the yeast and get a sense of its vitality.

Yeast Cell Counting

Yeast cell counting is a critical part of fermenting any food or beverage. For brewers and winemakers actively producing multiple batches of beer or wine, you want to stay on top of the viability of your yeast. You can do this by monitoring your yeast before fermentation and during fermentation, which really means after primary fermentation ends.


The first reason we count yeast cells is to know how much yeast we’re pitching and to determine the viability. When pitching yeast into a batch of wort of must, you’ll want a high percentage of viability. Viability refers to how many of the cells in your slurry (or batch of yeast) are actually alive. Dead yeast cells won’t do much for your batch beyond providing nutrients for your live yeast cells to feed on during fermentation.

Test Your Yeast


While it is rare, it has happened where a batch of yeast slurry arrives and many of the yeast cells are dead and useless to the fermentation process. If you pitch slurry with a lot of dead yeast cells, the live, viable yeast cells are more likely to get overwhelmed and stressed. Stressed yeast cells will cause a stagnant fermentation, which can create many more problems than it is worth.

For this reason, you will want to do a viability check.

Get access For Free to a detailed manual (25 pages) describing all the steps of the yeast repitching process!


Vitality is another issue you want to address when dealing with yeast cells. Vitality refers to how healthy the yeast cells are in a particular batch. While it is almost impossible to determine vitality of cells, you can typically trust that a slurry with a healthy number of viable cells will also have a high vitality rate.

In general, you want to see 85% or higher viability in your yeast cells. This means that 85% or more of the yeast cells in your slurry are alive and active.

Why Count Yeast Cells During Fermentation

But why do you need to count the yeast cells during fermentation? Isn’t a count before fermentation enough?

Well, when it comes to pitching, yes. As long as you know you have a viability rate of 85% or higher before fermentation, you can trust you will have a strong batch that will ferment well. Furthermore, you can record how each batch of yeast cells performs, including the viability percentage, so that going forward you know what to expect.

But most brewers also want to harvest, store, and reuse the yeast slurry after fermentation. With healthy yeast slurry, you can get at least another five pitches from that single batch, and sometimes up to ten.

You can also grow your yeast in a yeast brink, so that you don’t have to continue to purchase yeast from a supplier. Once you get a batch going that you like, there is no reason to ever give up on it.

For this reason, you want to count the yeast cells during fermentation as well, so you understand how the brewing or winemaking process affected the cells.

Typically, during fermentation, yeast cells will consume the sugars in the wort or must, convert those sugars to alcohol and wine, nourish themselves on dead yeast cells and other nutrients in the batch, and reproduce asexually, providing more yeast cells in your batch to ferment for you.

This process is a win/win for the brewer or winemaker as you are both making beer or wine and cultivating more yeast for future batches.

Thus, it is essential to understand the health and viability of your yeast cells at every stage along the way – once before fermentation, and once after primary fermentation has begun. If you rack your beer or wine and allow your yeast to undergo secondary fermentation, any remaining yeast can also be harvested, and the cells counted and included in future batches.

How to Perform a Yeast Cell Count During Fermentation

To count your yeast cells and check viability, you will perform the same process you do when you count cells before fermentation.

You will need:

  • Microscope with 400x magnification
  • Hemocytometer
  • 3 – 100 ml volumetric flask
  • Pasteur pipette
  • Clicker or counter
  • Methylene violet dye
  • Water

The first thing you will do is dilute your yeast sample so that you can actually count the cells on the hemocytometer.

For all the steps to be done from here on, with images and examples for two of the most common counting chambers – Thoma and Neubauer improved, download our Free Guide on Manual Cell Counting.

Automated yeast counting

If you don’t want to go through all the trouble of counting your yeast cells, you don’t have to! To save time, avoid the risk of human error, which is all but inevitable, and get accurate results every time, regardless of who’s doing the counts, you can opt instead for an automated yeast cell counter, which will allow you to load your diluted and stained yeast into a chamber and get instant results – both for cell count and viability.

You can now test the Oculyze automated yeast cell counter for free.



Are you still pitching fresh yeast every time? By reusing your yeast, you can save up to hundreds of thousands of dollars per year on just yeast alone!

Join the hundreds of brewers from all around the world using the Smartest Automated Yeast Cell Counter! Request a Free Demo Account today and experience firsthand how Oculyze can take your brewery to the next level!

Stay on top on important fermentation insights – subscribe to our monthly newsletter and receive a hand-picked selection of our most relevant articles straight to your inbox.

    Never miss a beat and get real time updates with a new article each workday by subscribing our social media channels.
    Instagram | Facebook | Twitter | YouTube

  • Publications

    What Is Bioethanol Made From?

    Have you been wondering, “What Is Bioethanol Made From?” This article explains the history of bioethanol and describes the resources used and the process.

    Read more
  • Publications

    Best Pattern Recognition Software

    A review of the best pattern recognition software for those interested in the various applications, including colony counts, bacteria identification, and more.

    Read more
  • Publications

    Petri Dish Bacteria Identification Chart: Why Use One

    This article is dedicated to those in the lab wondering whether a comprehensive petri dish bacteria identification chart could make their job easier.

    Read more
  • 0
      Your Cart
      Your cart is empty