Does Wine Yeast Need Nutrients?

Does Wine Yeast Need Nutrients?

Does Wine Yeast Need Nutrients?

As home winemakers, we know that wine yeast is an important element in winemaking. This microorganism is responsible for transforming grape must or juice into wine through a complex yet fascinating process called fermentation.

Yeasts are naturally present in nature and most of the times they are also naturally present in the must. For this reason, many inexpert winemakers believe that if it is not necessary to add yeast to the wine, it is also unnecessary to think about yeast nutrients.

But after all, does wine yeast need nutrients? Read on to find it out!

Types Of Yeast Used In Winemaking

Yeasts are microorganisms consisting of a single cell and classified as fungi. The research carried out on these microorganisms over the years led to the identification of over a thousand different species. Each type of yeast has its own characteristics although they all share the same biologic principles.

Yeasts are classified into two major categories, aerobic and anaerobic. The two categories distinguish the yeasts based on their breathing method. The first ones use aerobic breathing, meaning they need oxygen to maintain life. The latter, in the absence of oxygen, adopt an anaerobic respiration process commonly known as fermentation.

The anaerobic yeasts produce energy from the conversion of sugar into carbon dioxide and alcohol and this type of yeast is involved in the transformation of grape must into wine.

The fermentation process ends with the death of yeast, as the increased concentration of alcohol in the beverage will cause the death of the yeast cell. However, because different strains of yeast have different sensitivity and resistance to alcohol concentrations it is possible to obtain wines with different alcoholic content.

There are numerous types of anaerobic yeasts suitable for the production of ethyl alcohol yet two species are predominantly used in enology:
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    Saccharomyces Cerevisiae
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    Saccharomyces Bayanus

The first one is also commonly used for fermenting beer or leavening bakery products.

Yeasts involved in winemaking are also divided into multiple categories based on their shape. Although different types of yeasts are responsible for wine fermentation, the most important ones are classified as elliptical and apiculate. Both types mentioned above belong to the elliptical family.

From the apiculate family, a type of yeast responsible for wine fermentation is Kloechera Apiculata. This yeast is responsible for the activation of the alcoholic fermentation which will be subsequently completed by Saccharomyces.

The resistance to alcohol differs from yeast to yeast and the type involved in the winemaking process will determine the final alcohol concentration of the wine.

From all the yeasts reminded above, Kloechera Apiculata has the least resistance to alcohol and it dies when the concentration rises between 3% and 4%.

Saccharomyces Cerevisiae species resists to concentrations up to 16 or 17% while Saccharomyces Bayanus withstand higher concentrations.

Another important difference between the various species of yeast is the alcohol yield. Some yeasts need more sugar to produce the same amount of alcohol and for this reason, if you are using commercial yeast, it is recommended to choose the type wisely.  

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    Kloechera Apiculata species need a concentration of about 22 grams of sugar per liter to produce 1% ethyl alcohol;
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    Saccharomyces Bayanus requires 20 grams of sugar per liter to produce the same amount of alcohol;
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    Saccharomyces Cerevisiae only needs about 18 grams of sugar per liter to make 1% ethyl alcohol.

This means that the amount of ethyl alcohol produced by the fermentation of the must will vary according to the species of the yeast.

Apart from the basic nutritive necessities, there are many other factors that govern fermentation and yeast activity. Among these factors, sulfur dioxide is probably the most important. Sulfur dioxide affects not only the vitality but also the function of the yeast.

The two types of Saccharomyces yeasts are more resistant to sulfur dioxide and more effective in fermentation. For this reason, some winemakers choose to add sulfur dioxide to the must and kill Kloechera Apiculata before the beginning of the fermentation process.

This is a controversial practice and some claim there is no real benefit of such action. The sustainers claim that killing Kloechera Apiculata serves to perform a better alcoholic fermentation.

Does Wine Yeast Need Nutrients?

Wine Yeast

Returning to the main question, does wine yeast need nutrients after all? Yes! In the same way in which you need nutrients to perform your daily chores.

However, there is to say that in the case of wine yeast, the nutrients don’t include sugar, the main food of the yeast.

In fact, sugar is already present in the grape must and you will never have to add it if you use high-quality fruit. Nevertheless, yeast nutrient doesn’t mean specifically sugar. There are numerous other substances yeast need and that are not always found in the must.

These nutrients include minerals and vitamins as well as some other chemical elements such as the nitrogen.

Let’s see what nutrients your wine yeast needs and how to provide them to it!

What Nutrients Does Wine Yeast Need?

So, if wine yeast doesn’t need sugar, what nutrients should you give it? To understand what nutrients you should supply to the yeast, let’s have a look at its nutritional needs.

Sugar

Sugar is the main nutrient wine yeast needs. In most of the cases, you will not have to supply it as grape must or juice usually has plenty. Moreover, the most renowned winemakers always advise against the use of sugar additives in winemaking as it lowers the quality of the wine.

Nevertheless, in some cases adding sugar is permissible. In home winemaking, it is possible adding sugar if you’re using grapes of a lower quality with a low sugar content or if fermentation doesn’t start.

Nitrogen

After sugar, wine yeast needs nitrogen to thrive. Nitrogen isn’t naturally present in grape must and it normally needs to be supplemented if you aim to have an uninterrupted fermentation. In fact, a deficiency in nitrogen can lead to slow fermentation or the process could even be interrupted completely.

As explained above, different strains of yeast have different nutritional requirements and this applies to nitrogen too. For this reason, it is important to know the nitrogen requirements of the yeast you are using to be able to provide an adequate nitrogen supply.

Keep in mind that nitrogen content can be reduced by some inadequate winemaking processes, especially if you don’t control the growth of unwanted bacteria and yeasts. In most of the cases this problem is attributed to a low content of sulfur dioxide in wine and this is why some winemakers promote its use.

Regarding nitrogen, you should also know that not all nitrogen present in must is available for the yeasts to use. The portion of nitrogen wine yeast can use is referred to as yeast assimilable nitrogen (YAN) and is constituted majorly by ammonium ions and alpha amino acids.

Generally, wine yeast needs about 150 mg of YAN per liter of grape must for the fermentation to start and it is advisable to supply the yeast with at least 400 mg of nitrogen per liter to achieve a flawless fermentation.

We should also mention that wine yeast has a preference for the ammonium ions rather than for the alpha amino acids. This is why commercially available nutrients contain only diammonium hydrogen phosphate.

While supplying this nutrient to the yeast is essential, you should pay attention to how many nutrients you add. Keep in mind that grape juice contains a number of amino acids such as arginine and proline, and these amino acids should be consumed by the yeast if you want to obtain a quality wine.

Vitamins

Yeast will start the fermentation process with or without them, but some vitamins help to produce a healthy fermentation. Most vitamins wine yeast need are provided by the grapes and include biotin, riboflavin, thiamin, and folic acid.

However, some winemaking practices can reduce the vitamin content of must and in these cases vitamins, majorly thiamin should be provided to reduce fermentation problems.

Vitamin supplements for wine yeast are available commercially and also included in winemaking kits along with other yeast nutrients.

Types Of Wine Yeast Nutrients Used In Winemaking

There are a number of different wine yeast nutrients available commercially and choosing the right one is often confusing.

Complex Wine Yeast Nutrients

Most winemakers prefer the complex yeast nutrients that contain inactivated yeast and ammonium salts, usually diammonium hydrogen phosphate. Inactivated yeast is used as a source of vitamins and minerals and some nutrients even contain yeast extract.

Yeast extract has a strong flavor and it can affect the aroma of the wine in a negative way but it represents a great source of nutrients as it has a high concentration of organic nitrogen. For this reason, I’d suggest using high-quality complex yeast nutrients with yeast extract coming from a reliable source.

Rehydration Wine Yeast Nutrients

The difference between complex and rehydration wine yeast nutrients is the lack of ammonium salts in the latter. These nutrients contain inactivated yeasts and a supplement of minerals and vitamins.

This type of wine yeast nutrient not only represents a great source of essential fermentation elements but is also often used as flavor enhancement; its positive effect has been demonstrated on the Sauvignon Blanc but many other wines benefit from this type of nutrient.

Organic Wine Yeast Nutrients

If you want to make organic wine, then it is crucial to use organic wine yeast nutrients. These nutrients contain only partially lysed inactivated yeasts that are rich in amino acids and represent a natural source of organic nitrogen.

These nutrients don’t contain any inorganic substances yet only the certified ones as guaranteed as being organic.

Final Thoughts

Except for the nitrogen, wine yeast shouldn’t need other nutritional supplements. Nevertheless, wine yeast needs nutrients and you should be careful in choosing only the ones of the highest quality to ensure the quality of your beverage.

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