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Rioja winemaking
Quality Factors
Fermentation Classical vatting Typical Vatting Methods White Wines Rosé Wines Yeasts Devatting Pressing December racking Machinery used in the Bodega
Wine in the bottle
Wine tasting and analysis
Short history of La Rioja Alta, S.A


Yeasts are microbes which carry out fermentation, transforming sugared must into wine; a liquid with alcohol and without sugar.

Fermentation of Rioja wine seen under 1200 times magnification

Yeasts live in our environment and arrive at the bodega adhering to the skin of the grapes. Afterwards, they multiply in the must and act energetically.

Beer, bread, sake, ketir and kumis are food products made with yeasts.

Yeasts are not pathogenic elements for man, at least not those found on grapes, in vineyards and bodegas.

On the other hand, they themselves represent a food of enormous value, they are rich in nitrogen and vitamins. A fermenting must would be much more nutritious than still must orwine.

There are several types of yeasts which cause the fermentation of Rioja wine. Those which begin the fermentation are always yeasts which take advantage of the air present in the must. When they have consumed the air they die and those which do not need air, i.e., those which cause the fermentation, become active. These strictly fermenting yeasts belong to the Saccharomyces type.

The size of yeasts ranges from three to six thousandths of a millimetre. When grapes are pressed, there are usually fifty yeasts per cubic centimetre. In the middle of the fermentation process, there are one hundred million per cubic centimetre. Formerly, yeasts (of which there are many types) were classified according to shape, as observed under a microscope; but today it is necessary to resort to physiological tests in order to classify them.

Of the five hundred types associated with fermentation and food which have been classified throughout the world, only fifty are to be found in the vineyards, bodegas and wines. Of these, in La Rioja, we could say that only about five species are of any importance. We have found that when wines are of high quality, the following species are found in the fermentation of Rioja wine: Initially, Metsnikowa pulcherrima. Until half way through the process, Saccharomyces rosei. From half way to the end of the process, Saccharomyces cerevisiae.

These names are certainly very strange for the uninitiated but nevertheless, even if technicians did not know them, it would be possible to obtain (in general terms) the same excellent wines which our predecessors were able to produce. The yeasts which make red wines of the Rioja are the same as those which produce whites and rosés.

In some cases, when the harvested grapes are very cold on arrival at the bodega, or when they have been exposed to heavy autumn rain and their yeast has been washed away, yeasts are provided by means of a "pie de cuba". This consists of keeping a small amount of the same must from another part of the bodega, at about 25· C, to activate the yeasts and then transfer them to the mass of harvested grapes which require fermentation.

Imagen de portada

There was a time when it was believed that yeasts were a prodigious element and that by incorporating a Rioja yeast, for example, in musts from other regions, Rioja wine could be obtained. Tests were even made with a yeast from Jerez in musts from La Mancha in order to obtain Rioja wine. This change is not possible as the type of wine is influenced by a variety of grape, its genetic characteristics and environment.

Some yeasts spoil bottled wines. When a kind of "cream" appears on the surface of a wine in bottle, this means that the wine has a low alcohol content and the "cream" is in fact millions of yeasts cells. This could happen in any weak Rioja red wine.

In other regions, wine is conserved with "la madre" in the vats. This term defines the yeasts which transform the wine but also defend it from the attack of bacteria which make it vinegary.

Bottled Rioja wines withstand attack by yeasts. Reds are seldom attacked, which is one advantage of our Rioja. On the other hand, whites and rosés are affected by yeasts which produce sediment in the form of small balls, (millions of agglutinated yeasts), or a powdery sediment or a general cloudiness.

For this reason, whites and rosés are filtered before bottling, but not Rioja reds. If yeasts live basically on the sugar present in the grape, one could ask how they react in wine which does not contain sugar. The answer is simple.

Yeasts prefer to feed on sugar, but when there is a lack of it some yeasts (not all) feed on the alcohol, especially when the bottle has a large air space or when the cork is not up to standard.

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