From the Fall 2000

by Daniel Pambianchi of WineMaker magazine

Montrachet or Prise de Mousse? No matter what style of wine you're making, you have to pick the right yeast for the job. Plus: a guide to leading home-winemaking strains.

Wine is made in the vineyard. "It's the terroir," the French will say. Or is it the winemaker's craftsmanship that makes the wine?

What gives wine its bouquet, aroma, structure and balance? That's a much-debated topic in winemaking circles. In spite of the many opinions, no one can dispute this fact: You need to select the right kind of yeast for the style of wine you want to make. Yet choosing the proper yeast should not be a daunting task - with proper planning it's easy to achieve the desired results.

Yeasts are essentially fungi found in, and then isolated from, such environments as soil, plants and fruits. Specific yeasts - called "strains" - have different morphological (physical appearance) and physiological attributes that characterize their behavior during the fermentation process. Different yeast strains will therefore produce wines with different characteristics, such as aromas, alcohol level, acidity and body.

First, you need to determine the type of wine you wish to produce. Will it be red, white, rosé, dessert? The desired style is based on the many factors: the varietal used; whether you are fermenting must from grapes, sterilized juice or a kit; the fermentation environment (temperature, sugar content and other factors); and whether malolactic fermentation (MLF) is desired. It is also based on the specific characteristics imparted by the chosen yeast (such as flocculation and production of SO2, volatile acidity and hydrogen sulphide).

The Role of Yeast

Wine yeast comprises microorganisms responsible for converting the sugar in grape juice into alcohol. Alcoholic fermentation is the single most important aspect of winemaking. It is at this stage that wine starts developing its flavors, aromas, body and structure. Yet, all too often, home winemakers pay too little attention to selecting the proper yeast. The end result may be a wine that does not reflect a desired style or that has off-flavors.

Types of Yeast Strains

French winemakers, especially Burgundians, still conduct alcoholic fermentation using wild (indigenous) yeasts that have formed on grape skins while on the vines. Commercial wineries have a full-time staff dedicated to wine analysis and to the close supervision and control of fermentation. Wild yeast fermentation is unpredictable and can be troublesome, because it is more susceptible to lower levels of SO2 and alcohol. The result can be a stuck fermentation. Wild yeast fermentation is also prone to microbial spoilage if not managed properly and is best left to professional winemakers.

Cultured wine yeasts, which are isolated, bred and characterized for behavior in laboratories, on the other hand, allow for a risk-free fermentation with relatively minimal monitoring since the results are highly predictable. Manufacturers of cultured wine yeasts provide a lot of data on strain characteristics and expected results (for a rundown on leading strains, click on "Yeast Strains Chart" in the vertical column at left).

For home winemaking using grapes or fresh juice, it is best to inhibit wild yeasts using a small dose of SO2; home winemakers do this by adding potassium metabisulphite to achieve a maximum free SO2 level of 10 mg/L. You should also use yeasts that have been cultured specifically for the desired wine style. Concentrated and sterilized grape juices have been stripped of all yeasts during production, therefore, they always require the addition of a cultured yeast.

The most common and readily available cultured wine yeasts for home winemaking are strains of the cerevisiae and bayanus species from the Saccharomyces (S.) genus. S. fermentati strains are also available for sherry-style wines. Within a species, there are many strains, each with different physiological attributes intended for different applications and yielding different vinification results.

Leading manufacturers of wine yeasts include Lallemand (Lalvin), Universal Foods Corporation (RED STAR), Wyeast (Vintner's Choice), and White Labs. Commercial yeast strains are identified by a marketing name and, often, a cryptic strain code. The marketing name may include the geographical name where the strain was isolated. An example is Pasteur Champagne yeast, isolated in the Champagne region of France, which actually is not meant for Champagne or other sparkling wines.

A word of caution! Some yeast strains are marketed using strictly French appellation names, such as Sauternes Yeast or Champagne Yeast, without any indication of the specific strain. These may impart some of the aromas and flavors found in these commercial styles of wines. To replicate these famous wines, however, you also need to achieve the right balance between residual sugar, alcohol level and acidity. These "appellation" yeast strains are not responsible for providing this balance. You should always ask your retailer for the manufacturer's technical data. Cultured wine yeasts should provide you with expected results.

Below, we provide an overview of some of the more popular home-winemaking yeast strains. Different manufacturers may have different marketing names for the same strain. Compare the technical data to establish similarities or differences in fermentation behavior and expected results.

S. bayanus Strains

California Champagne is the yeast of choice for méthode champenoise (bottle-fermented) sparkling wines. Its excellent flocculation properties cause the lees to be tightly compacted, therefore providing a clearer wine. It also imparts a yeasty flavor typical of these wines.

EC-1118 (or Prise de Mousse) is recommended for wines to be barrel-fermented, for difficult fermentations or to restart a stuck fermentation. It can be used for red and white wines but it is ideal for sparkling and sweet wines. It has a good tolerance to free SO2 and higher alcohol content, can ferment at much cooler temperatures, has good flocculation properties, and inhibits malolactic fermentation (for more on malolactic fermentation, see below). Four-week wine kits are usually packaged with this yeast strain to enable a quick and trouble-free fermentation.

Pasteur Champagne is recommended for dry white wines. This strain, isolated in the Champagne region, is not meant for sparkling wines. It has a good tolerance to free SO2, has good flocculation properties, and can also be used to restart a stuck fermentation.

S. cerevisiae Strains

71B-1122 is used mainly in the production of fruity and aromatic wines, such as rosés and white wines in which residual sugar is desired. It also favors malolactic fermentation, has a good tolerance to higher alcohol levels, and produces very little SO2. Aromatic Muscat-based wines will benefit the most from this strain.

D47 is the best choice for premium-quality white wines including Chardonnay, Sauvignon Blanc, Sémillon, Riesling, Gewürztraminer. and Viognier. It also favors malolactic fermentation. It 's not recommended for red wines.

Epernay II is recommended for wines in which fruit flavors are to be enhanced or residual sugar is desired. It should be used with yeast nutrients since it has a slower rate of fermentation that may cause it to stop, especially at cooler temperatures. It is ideal for Riesling and Gewürztraminer wines. Wines that will undergo malolactic fermentation will benefit from this strain.

K1-V1116 is used in wines where varietal expression is desired. Grape varieties that benefit most from this strain include Sauvignon Blanc, Sémillon and Chenin Blanc. This strain is also recommended for low-nutrient musts or to restart a stuck fermentation. It has good tolerance to higher levels of alcohol.

Montrachet is recommended for full-bodied, intense-color red and white wines with complex flavors such as Chardonnay. It has a good tolerance to free SO2. A major drawback of this strain is the high level of hydrogen sulphide produced, which can be particularly problematic when using grapes with sulphur residue on the skins.

Pasteur Red is recommended for full-bodied, tannic red wines where varietal fruit flavors and complex aromas are desired. This strain is ideal for Cabernet Sauvignon, Merlot and Syrah wines, and when malolactic is desired.

RC 212 is recommended for red varieties where full tannin and color stabilization are desired, and to favor malolactic fermentation. Burgundian varietals such as Pinot Noir are best fermented using this strain.

S. fermentati Strain

Flor Sherry is used in the production of sherry-style wines. It is responsible for imparting those common nutty and maderized flavors through the oxidation (aerobic fermentation) process.

Fermentation Temperature

Alcoholic fermentation should always be carried out within the manufacturer's recommended temperature range. A temperature that's too cold can cause the yeast to remain dormant and inactive, resulting in a stuck fermentation. It could also cause an explosion if the partially fermented wine is bottled. Likewise, high temperature can annihilate the yeast. Ideally, fermentation should be carried out in a room where the temperature can be controlled and where variations are minimal. Fermentation temperature, especially for reds from grapes, can easily exceed 90° F (32° C) if the environment is too warm - greater than 68° F (20° C).

Reds should be fermented between 72° and 82° F (22° and 28° C) while whites are best fermented between 50° and 57° F (10° and 14° C). Make sure that the fermentation has started and is vigorous before transferring your carboys to a cooler temperature when fermenting whites. Fermenting at the low end of the range becomes risky.

A S. bayanus strain, such as the EC-1118 (Prise de Mousse), is recommended if temperature variations cannot be controlled or if approaching the upper or lower temperature limit. This strain can remain active in a range of 45° to 95° F (7° to 35° C) and is therefore ideal for restarting stuck fermentation due to temperature.

A low-temperature tolerant S. bayanus or S. cerevisiae yeast strain is recommended for either white wine vinification, or for red wine vinification from kits or juice where a slow fermentation is desired to impart maximum flavor to the wine. If the temperature is high, the rate of fermentation will increase considerably and full flavors will not be extracted.

Red wine vinification from grapes is more of a challenge, as the fermentation temperature quickly rises on its own accord. It can be quite difficult for home winemakers to lower the rapidly rising temperature and to avoid exceeding the upper threshold. The higher temperature does provide for greater extraction of the phenolic compounds found in red wine grapes, but at the expense of flavor. A long and slow fermentation at a low temperature using a S. cerevisiae will provide maximum extraction of phenolic compounds and flavors, resulting in a more full-bodied wine with greater color depth and more tannin. Remember that the challenge is to bring the temperature back down from, for example, 90° F (32° C) down to 68° F (20° C) to prevent an overly fast fermentation.

Alcohol Tolerance

The next important consideration in the selection of a yeast strain is the (fermentable) sugar content of the must. The amount of potential alcohol in a wine is directly proportional to the sugar content. Certain strains are less tolerant to high alcohol levels and may therefore become inactive resulting in a stuck fermentation.

Many S. bayanus and S. cerevisiae yeast strains can tolerate up to 15% alcohol by volume. These are adequate for musts with normal sugar content as most wines will result in 11 to 13.5% alcohol.

Some S. bayanus (such as Prise de Mousse) and S. cerevisiae strains (such as 71B-1122 and K1V-1116) can tolerate up to 18% alcohol. These are recommended for the production of high alcohol wines that required some residual sugar, such as a Sauternes or port-style wines. They also work well in musts with a high sugar content that you want to ferment to dryness.

Flocculation

Flocculation refers to the yeast's ability to produce a compact mass of lees (sediment) once fermentation is complete. A high-flocculant yeast greatly simplifies racking of the wine, produces a clearer wine, and minimizes volume loss.

If you bottle wine without any fining or filtering, you should select a high flocculant yeast to compact the lees as much as possible. Still, multiple rackings are recommended to avoid deposits in the bottle. A less flocculant yeast may be selected for wines to be fined or filtered. Flocculation can be controlled during fining since clarifying agents also compact the lees to varying degrees. Filter pads should be chosen as a function of flocculation properties to avoid pads getting clogged during filtration. Use a low-numbered filter pad, such as a #1 or #2, followed by a higher-numbered pad, such as a #2 or #2, if necessary. For bottle-fermented sparkling wines, a high flocculant yeast should be used to create compact lees .

Malolactic Fermentation (MLF)

Malolactic fermentation, through the presence of Leuconostoc oenos bacteria found in fresh juice and grape musts, converts the sharper, naturally occurring malic acid into the softer lactic acid. By doing so, it makes wines more approachable and gives them an added dimension and complexity. It is most beneficial in red wines and is generally not recommended for white wines, except for Chardonnay or highly acidic grape varieties. A culture of L. oenos bacteria can be added to kit wines or sterilized juices if MLF is desired.

A S. cerevisiae yeast strain specifically recommended for MLF should be used to ensure that the L. oenos bacteria become active and complete the malolactic process. S. bayanus yeast strains should not be used when MLF is desired, because L. oenos bacteria is sensitive to the higher levels of SO2 produced during the alcoholic fermentation.

MLF bacteria should be added near or at the end of alcoholic fermentation, when the Brix reading is less than 5° or the specific gravity is less than 1.020. MLF will require between one to 3 months to complete. A paper chromatography kit, which you can buy at a winemaking supply shop, should be used to monitor MLF progress and to determine when it has completed. Be sure to always observe the manufacturer's recommendations on free SO2 level, pH, temperature, and other specified environmental conditions. If you don't do this, the necessary bacteria cannot survive. This will cause MLF to become stuck - or to never start.

A S. bayanus yeast strain is recommended in the production of sparkling wines where MLF is not desired during bottle fermentation.

Yeast Nutrients

Yeasts have different physiological attributes, so their behavior during fermentation (for example, the multiplication rate of yeast cells) will be different depending on the environmental conditions. For example, a high sugar concentration will cause the yeast to struggle and may cause the fermentation to be sluggish.

The addition of yeast nutrients may be required for various instances: if you're producing wines in which the yeast will be subjected to adverse fermentation conditions; as a preventative measure when the source and quality of fruit or juice cannot be ascertained; or when the grapes are deficient in yeast nutrients. Grapes from a poor, rainy, or a rot-affected vintage will typically be deficient in yeast nutrients. In such cases, yeast nutrients are recommended to favor yeast multiplication and fermentation. Certain yeast strains, such as the Epernay II, will also need additional nutrients.

Yeast nutrients are available in powder form and are pre-mixed with all the ingredients necessary to favor yeast cell multiplication. These include diammonium phosphate (DAP), thiamin (vitamin B1), biotin and riboflavin. Thiamin is the most important vitamin in yeast nutrients.

The addition of yeast nutrients is always recommended when making wine from concentrate or sterilized juice. These pasteurized or sterilized musts are often deficient in yeast nutrients. Yeast nutrients are not required, but are recommended, when using fresh juice or grapes. Most often, yeast nutrients are used when fermentation is stuck - along with fresh healthy yeast - or when fermentation is to be carried out in a high-sugar or a high-alcohol environment. As yeast nutrients will favor fermentation of sugar into alcohol, the finished wine will be of higher alcohol content. They should be added at a rate of 10 to 20 g/hL (hL=100 L) by first dissolving the nutrients in water. When required to add nutrients under normal conditions, these should be added before the start of alcoholic fermentation, at yeast inoculation.

Other Factors

Yeast manufacturers often include other specifications, such as foam production and volatile acid, SO2 and hydrogen sulphide productions. These are generally not of significant concern to home winemakers.

Fermentation vessels should always be filled to approximately two-thirds capacity in preparation for the alcoholic fermentation, which will produce considerable foaming. This is a good rule of thumb for all yeast strains, even though some will foam less.

Volatile acids affect the quality of wines and potentially cause spoilage. In large quantities, these acids are undesirable, and a yeast strain that minimizes the production of volatile acidity should be selected. Note, however, that in small quantities, volatile acidity is a vital component of a wine's bouquet.

Although minute quantities of SO2 are produced during fermentation, a yeast strain with very low SO2 production should be used. This is particularly recommended when SO2 levels cannot be measured and the wine is to undergo MLF. Both yeast and MLF bacteria are very sensitive to SO2 and will not survive if specified thresholds are exceeded.

Hydrogen sulphide in excessive amounts can be detected as an unpleasant rotten-egg smell. Both S. bayanus and S. cerevisiae yeast species, even when properly fed, may produce minuscule quantities of hydrogen sulphide that cannot be detected by smell and are not harmful to wine. Avoid yeast strains, such as the Montrachet, which are specified with a high hydrogen sulphide production.

Always ask for the manufacturer's specifications when buying yeast to ensure that it will be compatible with the wine to be produced.

Yeast Preparation

Cultured wine yeasts are available in both dry and liquid formats, the latter being more expensive. The most popular kind is active dry wine yeast. It's more stable than the liquid format and therefore has a longer shelf life - approximately 18 months - if kept away from moisture and refrigerated between 40° and 50° F (4° and 10° C). Liquid cultures should be used within a month. Liquid cultures, unlike their dry counterparts, do not require rehydration and can be added directly to the must. Be sure to always follow the manufacturer's instructions to avoid any fermentation problems down the line.

Active dry yeast is commonly available in 0.176 oz. (5 g) packets - good for 1 to 6 US gal (4.5 to 23 L) of must. Use multiple packets for larger volumes if you can't find the larger formats. Dry packets should be rehydrated, following the manufacturer's instructions in a small volume of water at the recommended temperature, without exceeding the recommended rehydration period. A container with a capacity of at least double the water volume should be used, as rehydrating yeast will bubble up. The hydrated yeast culture, or inoculum, is added directly to the must and then stirred thoroughly.

The use of a "yeast starter" is often recommended as an inoculum to favor a successful fermentation when using grapes or when fermenting under difficult conditions; for example, where the cellar temperature is rather cool.

A yeast starter is prepared by using a 2 percent volume of must and adding yeast to start fermentation. This is done several days before inoculation of the entire must. Optionally, yeast nutrients can be added if a difficult fermentation is anticipated. The yeast starter should be at room temperature, and once fermentation is vigorous, it is added to the bulk of the must.

Cultured yeast should always be stored in a cool, dry place such as a refrigerator. Maintain a supply for a single vintage or one year only and always rotate your stock. Discard any opened packets. Packets that are no longer fresh may cause fermentation problems.

Happy Yeasting!

Winemaking involves myriad decisions, and each choice you make will determine whether your wine is mediocre or sublime. So next time you start a batch, choose your yeast carefully. It could make a world of difference in the finished wine. Happy yeasting!