Yeast and Winemaking: Everything You Need To Know


Do you see any yeast on your screen? Probably not, but there’s a good chance there are some that aren’t visible to your eyes. Similarly, yeast is everywhere. It covers most surfaces and reaches most hidden corners.

In the context of wine, yeast is the central ingredient needed for fruit juice to turn into the intoxicating drink that we all know and love. Wild yeasts, those that have not been processed in a lab, are found on the surface of various fruits and they initiate the process of fermentation under the right conditions.

Yeast turns the natural sugars in fruits to alcohol and releases the aromas one associates with wine that are packed within the sugar. There is much to know about how yeast affects the winemaking process, and the bottle served to you at the end of it.

In this article, we’ll discuss all things related to yeast and winemaking. The type of yeast a winemaker uses can significantly alter the characteristics of their product beyond the mere production of alcohol. To understand how this process works in greater detail, read on.

What is Yeast?

Yeasts are unicellular organisms that thrive on warm conditions, moisture, and sugar or starch. The word ‘yeast’ literally means ‘sugar fungus’. A Dutchman named Antoni van Leeuwenhoek first observed these sugar fungi in the late seventeenth century, and he was not impressed.

Believing them to be merely starch, the enormous utility of yeasts would not be discovered for another 150 years. In the mid-nineteenth century, Louis Pasteur finally proved that it is indeed yeasts that cause the juice to turn into wine.

Until then, very little was understood about how exactly the conversion took place. But this discovery changed the face of wine, and the food industry overall as well.

Types of Yeast

Different types of yeasts are used to make bread, wine, and bear. The one used for wine is called Saccharomyces bayanus. The saccharomyces cerevisiae can be used for both, bread and winemaking. Lastly, the saccharomyces pastorianus is used for beer production.

Besides bread and alcohol, yeast is used for a wide variety of things today. It used as an ingredient in skincare items, to make chocolate, as a replacement for cheese, to grow hair, and for much more. It is an everyday cooking and baking ingredient as well.

While purchasing yeasts, you can either get dry or wet (also called fresh) yeast. Winemakers use dry yeast, while bakers use fresh. There are many further types of dry yeasts worth exploring, but they are all classified as either active or instant.

Besides offering granules of differing size, the main difference between these types is that active yeast needs to be activated by mixing it with some water, while instant yeast does not require any assistance, and are designed so to make bread rise higher, faster.

As such, most winemakers utilize active yeasts. If you ever find yourself in a situation where you do not have active dry yeasts, you can use bread yeasts to ferment your wine as long as the alcohol content of your wine is below 8%.

But this comes at the cost of flavor as well, so do this only if wine yeasts are unavailable.

Yeast in Winemaking

Winemakers use yeast to convert the natural sugars of fruits into alcohol through a process called fermentation. This has the complementary effect of enhancing the flavor and aroma of the wine as well.

When yeasts are added to juice, it undergoes five steps before the wine is derived as the final product.

First, yeasts settle into the juice and adjust to the temperature, pH level, the availability of specific nutrients needed for yeast growth, etc. The initial stages are also when the yeast consumes many of these nutrients, and winemakers often have to replenish this stock to ensure that the yeasts don’t die.

Once 48 hours have passed, the yeast reproduces and multiplies exponentially before this growth eventually declines, and ends as all the dead yeast accumulates at the bottom. This end product is called ‘gross-lees’, and massively divides opinion in the wine world.

Many believe that it enhances the flavor and texture of the wine, but others prefer separating it from the liquid before consumption. But that could be based solely on the unfortunate name.

Ferment Juice

There are two ways to ferment juice using various types of dry yeasts.

The first is called wild fermentation. Its name derives from the fact that this process utilizes only the natural yeasts present on the skin of the fruits.

The second is called a controlled fermentation. This process uses artificial yeasts that destroy all the natural yeasts and guarantee a more uniform fermentation of the juice. Both of these will be covered in greater detail throughout the following sections.

Wild Fermentation

Wild fermentation was once the only way wine could be fermented, and it presented many debilitating problems for winemakers across the world. This type of fermentation relies on the presence of natural, uncultured yeasts that are present on the skin of fruits to intimate the process.

Due to the kind of changes yeast influences in wine, and the ease with which diffuses across air, each winery has several different strains of yeast covering its walls, vessels, and other nooks and crannies across the estate.

A successful wild fermentation will preserve all the distinctive features of a particular winery, and the area it is grown in. But here’s where it gets complicated.

Producers who opt to go for the wild route take a big risk of suffering from a stuck fermentation. This is the malaise that gripped many winemakers in the past centuries, often causing an entire year’s hard work to go to waste.

Stuck Fermentation

Stuck fermentation is when the process gets ‘stuck’, allowing for bacterial growth to take over the wine. This renders it undrinkable, and producers are left with no option but to deal with the losses.

Many factors could cause fermentation to pause, or end prematurely. Yeasts need specific nutrients that allow them to breed and convert more of the sugars to alcohol. They also require constant supervision from the winemaker to ensure that the process is proceeding as intended.

Two of the most essential elements that help cultivate fertile grounds for fermentation are oxygen and nitrogen.

Yeasts use oxygen to build new cell walls as the previous ones merge with the sugars to form alcohol. Nitrogen helps yeasts revive other parts of their cell and prevents the formation of hydrogen sulfide.

Glucose and Fructose, the natural sugars inside fruits, is the second group of essentials needed for fermentation. These two compounds are what yeasts feed on to release alcohol and carbon dioxide. To maximize the chances of a successful fermentation, a winemaker must ensure that his grapes are of the highest quality. They generally contain more nitrogen, more yeast, and more sugar to convert into wine.

Despite these issues, it has been reported that most wine today is still made through wild fermentation. Only around 20% of the wine produced globally is produced by controlled fermentation, while the rest relies on the over 50,000 strains of yeast one can come across on a single grape.

Controlled Fermentation

Some time in the 1960s and 70s, scientists began to isolate the Saccharomyces species of strains from its environment, where it is found mixed with other strains.

Many natural types of yeast find it hard to survive in juice of high alcohol content (above 4%), and if there are traces of Saccharomyces in a winery, they generally finish the process of fermentation under the right conditions. They are also better at adapting to swings in temperature, oxygen levels, and most importantly, the quality of the grapes.

Cultured yeasts can ensure the completion of fermentation even with fruits of inferior quality, which tend to contain less essential nutrients required to carry out the process.

But many winemakers don’t wish to rely on the unpredictability of wild fermentation. One of the critical features of uncontrolled fermentation is that the wine from whichever winery uses this technique will vary from year to year depending on weather patterns, soil fertility, etc.

This can throw a spanner in the works of big businesses that operate on the promise of uniformity and consistent quality. A Cabernet Sauvignon, or a Reisling have specific taste palettes that cannot be interfered with, whereas small winemakers who make various table wines can afford to experiment with their techniques without risking a backlash.

Neither can they afford the potential losses that come with stuck fermentation, since a distribution schedule usually binds them. Using cultured yeasts gives the producers much greater control over the end product, which comes at the cost of more complex and rich flavors. But once the initial popularity of this form of fermentation faded, the natural and organic element of wild fermentation became a popular marketing ploy for many winemakers.

Yeast and Winemaking

Yeasts are one of the most diverse invisible species of organisms to inhabit this earth. They are everywhere, and many thousands of varieties of yeast can be found on grapes.

Since their discovery, yeast has changed the food industry in many fundamental ways, and the wine industry has been one of the biggest beneficiaries of this discovery. They have enabled the rise of controlled fermentation when once only wild and unpredictable methods were practiced.

This has improved global wine supply, standardized flavor palettes for famous wines, and assured quality year after year.

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