Fermentation tracking in winemaking

Monitoring the sugar levels, yeast viability, and temperature allows to control the fermentation process and react early enough if problems occur.

Fermentation is a dynamic yet steerable process. During the alcoholic fermentation process yeast cells convert the sugar in grapes into ethyl alcohol and carbon dioxide.

Due to the dynamic nature of the process and the importance of the fermentation conditions to the final product, it is important to know what is happening in the must. The sooner potential problems are addressed, the more likely the end product is to be as desired.


It is common practice to track fermentations by means of density meters such as an oscillating U-tube. A hydrometer allows to track the progress of the fermentation, control the alcohol content and determine when the wine is actually done fermenting.

Brix or Baume scale is commonly used to determine if the grapes have sufficient level of sugar for harvest, and if the must has enough sugar to produce the desired level of alcohol. A more precise estimation can be achieved by measuring the specific gravity (S.G.) of the juice.

The challenge of using these common tracking methods is that gravity follows the metabolic activity of yeast. It means that if you wait for your sugar content to deviate from your expectations you probably had an issue with your yeast 2-3 days ago. By the time you realize this your fermentation is sluggish if not stuck.

Test Your Yeast


There is still time to react, but you are 48 hours into the problem and no matter what you do, you will not get back the fermentation quality you had 48 hours ago.


One of the most important factors to track is the temperature. Yeast is very sensitive to temperature. Improper temperature is the number one reason for a fermentation to stop in mid-stream or for a fermentation to not start at all.

For a sound fermentation, fermentation temperatures should stay on an ideal level. If the temperature is too low, fermentation is very slow, or it doesn’t start at all. If it is too high, fermentation is very fast, and the flavor of the alcohol is often considered inferior.

When alcohol levels increase, the yeast cell walls become more permeable and sensitive to alcohol itself. A high fermentation temperature exacerbates this and can contribute to a stuck or sluggish fermentation.

Higher fermentation temperature may also attract unwanted micro-organisms to multiply more easily. That can ultimately lead to off-flavors, or, in extreme cases, complete spoilage of the wine.

Anti-stuck fermentation tactics like adding yeast hulls and adjusting temperature are commonly used in case the problem arises. Those methods don’t come without a risk however, as excessive heat at the end of fermentation can also exacerbate alcohol permeability and hasten cell death.


Wine yeast can be a culprit for a variety of wine faults either directly or indirectly. It can cause off flavors and aromas to wine or produce higher than ideal levels of certain by-products. It may also be behind stuck fermentation.

A careful analysis of yeast before and during the fermentation process is critical to the quality and consistency of the winemaking process. It enables winemakers to detect any problems as early as possible.

Free Yeast Analysis


The most common method for determining the number of yeast cells and their viability is manual counting on a standard microscope using a hemacytometer and methylene blue. Samples are taken during the pitching process, as well as at the end of the fermentation process.

However, the manual yeast counting method is laborious and has the problem of the operators being highly subjective. The data acquired is not easily traceable. Considering the cost of human labor and the possible counting errors, it’s not very affordable either, even if the equipment used might be relatively inexpensive.


The Oculyze FW is the first affordable alternative for analyzing the yeast population and observing the progress of fermentation in winemaking. With a mobile microscope and the application, any winemaker can transform their smartphone or tablet into powerful tools that allow to obtain precise results within seconds. The method is easy to use and doesn’t require any microbiological experience.

Controlling and managing the fermentation increases reliability in wine production and helps saving resources. Optimal starting conditions and continuous monitoring allow winemakers to react in an early stage in case of fermentation problems. A new warning feature even announces any deviations from the ideal fermentation curve as soon as the yeast runs into trouble.

Tracking fermentation with yeast counting can therefore help reach the full potential of the wines.

For more information on how you can control your fermentation and monitor your yeast with Oculyze FW, drop us a line at [email protected]!

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.

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