Winemaking Philosophy / Styles Series #3 – Fermentation

The grapes are in, the harvest is complete. What do we do from here?…well to make wine, the “must” has to be fermented. Ferment the grapes so that they can be barreled and bottled….done….not that easy or simple in the mind of a winemaker. Let’s focus on one of the most complex steps in winemaking.



In order for fermentation to take place, strains of yeast must be present in the wine. Simply put, yeast strains that are suitable for fermenting wines, interact with sugar molecules, and the result is CO2 gas and alcohol.

Here’s where things get complicated: There over 1,500 discovered strains of yeast, and they are present almost everywhere. Dozens of yeast strains could be present in a single vineyard, and some of them may be terrible for fermentation, producing spoilage that can ruin the wine completely.

So, most winemakers use sulfites to kill off indigenous yeasts, then inoculate with a yeast strain isolated by chemists for a fermentation that is much more predictable and reliable.


After de-stemming and crushing the grapes, sulfites are added to kill off wild yeasts. After this has stabilized, tests are done, and nutrients are added to the wine, the yeast of a winemaker’s choice is added…the fermentation process has begun….what do you mean by “yeast of a winemaker’s choice”?

Every yeast reacts with sugars and other molecules found in grapes slightly differently during fermentation. As an example:

Lalvin BM45 : It produces high levels of polysaccharides and therefore wines with increased mouthfeel. It tends to bring out aromas in Sangiovese described as fruit jams, rose and cherry liquors, with evident and clean notes of sweet spices, licorice and cedar. It also is used to minimize vegetal characteristics and can be used with Chardonnay as a blending component to increase mouthfeel. With a 16% alcohol toxicity ceiling, it reliably ferments to dryness.

Assmannshausen : Assmannshausen is a German yeast strain best suited for red wines. It intensifies the color and adds a spicy aroma. It first was only meant for Pinot Noir and Zinfandel, but now Cabernet Sauvignon takes advantage of this strain. The only drawback is its ineffectiveness in a high solid content.


As yeast ferments the sugars in the “must” into alcohol, winemakers do their best to regulate the temperature. Yeast performs differently at different temperatures, and therefore, taste can be affected by this temperature. Typically fermentation is done at temperature anywhere from 60degrees – 90degrees. Temperature is a catalyst and determines the rate at which fermentation takes place. If the temperature is too low, fermentation may stop, too hot and the result is a cooked flavor.

Every winemaker has his/her own idea of the perfect fermentation, but, it is seen by most that a cooler temperature will help in maintaining identity of the wine, the unique flavors from a vineyard that make it unique, as well as maintaining purity of flavors and especially aromatics. On the other hand, warmer temperatures can create a much more intense, powerful flavor, and can ensure that the yeast finished fermentation with no problems.


Every yeast can maintain fermentation only to a certain point. When making a dry red wine, winemakers want to use a yeast strain that can finish the fermentation, all the way to dryness (no sugar left). But if grapes are picked are picked at high brix levels, wines can reach as high as 17% alcohol. THAT’S REALLY HIGH! But most yeast can’t continue fermenting past 15% alcohol. So what does one do!? Pick yeast that ferments to 17%! But this will limit a winemaker’s options drastically as far as the flavors they want to impart on a wine from the yeast selection.


Indigenous yeast fermentation has been seeing quite a bit of interest in the last few years. There are a few reasons for this, but there are also some serious disadvantages to consider as a winemaker.


All yeasts impart certain flavors on a wine, but indigenous yeast imparts flavors unique to a single vineyard. Many wineries market their wines as unique, while they use the same yeasts that the majority of winemakers use. Indigenous yeast gives a winemaker something absolutely unique, a flavor that cannot be replicated elsewhere.


Not all indigenous yeasts are good yeasts. A winemaker must do their research and determine whether the yeast present will be suitable. If they are not, there will be some horrible results. Spoilage and other problems will reign supreme. Also the yeast present may not be strong enough to finish fermentation. Sometimes they won’t even continue past 12%, so it is crucial for a winemaker to ensure that the indigenous yeasts have enough power to reach dryness if that is their intention.


Using indigenous yeast can have massive affects on the quality of a wine as well as creating a unique flavor. Sometimes native yeast is just fantastic for fermentation, and can react with the grapes better than yeasts you can purchase and inoculate. A winemaker can maintain very low temperatures during fermentation, maintaining purity of fruit and aromatics, and fully fermenting until dry.



Many winemakers who prefer this type of winemaking use a philosophy of minimal intervention. They believe the best flavors that are available to them are already there in the vineyard, and to tamper with that will only work against them. It is their job to nurture what is given to them and build a strong foundation for it to lay at rest. After all, “we can harness the power of the wind but we cannot stop it”.



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