Saccharomyces cerevisiae : in the service of beer for 9 000 years

The preparation of beer begins with the addition of the yeast Saccharomyces cerevisiae to a wort consisting of a mixture of water and different cereals, one of which is barley. The yeast cells convert the sugar in the grain into alcohol and carbon dioxide. They also produce changes in the proteins and some of the other constituents of the mixture; this alters the taste and eventually transforms the wort into beer.

Saccharomyces cerevisiae : in the service of beer for 9 000 years

The preparation of beer begins with the addition of the yeast Saccharomyces cerevisiae to a wort consisting of a mixture of water and different cereals, one of which is barley. The yeast cells convert the sugar in the grain into alcohol and carbon dioxide. They also produce changes in the proteins and some of the other constituents of the mixture; this alters the taste and eventually transforms the wort into beer.


© Armand-Frappier Museum, 2008. All rights reserved.

Beer making

Every year, nearly 100 billion liters of a beverage, well known for over 10,000 years, are consumed. We are talking about beer!

Enormous fermentation vats contain the wort of several cereals, including barley. To obtain the wort, the cereals must be swollen in water and then heated. The liquid is then strained.

The yeast, Saccharomyces cerevisae, is then added to the wort. The fermentation begins. During this step, the yeasts convert the sugar in the cereals to alcohol and carbon dioxide; this is what produces small bubbles in the beer.

Of all the alcoholic beverages in the world, beer is the only one that is boiled. After the wort has boiled, the hops are added. Hops, the flowers of the Humulus lupulus plant, have been used to flavor beer since the 15th century.

The yeast comes from a strain that must first be isolated in a laboratory. Isolation must be carried out in sterile conditions, i.e., with material that contains no other microorganisms whatsoever.

Some beers, such as Blanche de Chambly, undergo a second fermentation. After the beer has been poured into the bottles, sugar is added, which re-activates the yeasts and provokes a second period of fermentation. There will therefore be more alcohol and carbon dioxide in this beer, which is called “beer on lees”.

To be consumed in moderation with some friends … A toast to your health!

Production Cinémanima inc. and Armand-Frappier Museum

© Production Cinémanima inc. and Armand-Frappier Museum


The yeast Saccharomyces cerevisiae is separated in a sterile manner from the medium made from the wort, which was providing it with the essential elements for growth. The growing yeast is then seeded first into tubes and then into Erlenmeyer flasks containing sterile wort. Two flasks are then used to inoculate the wort in a large 2 000-liter vat in which the yeast replicates for forty-eight hours, forming the yeast starter.

Illustration de Bruno Laporte

© Armand-Frappier Museum, 2008. All rights reserved.


The malted* cereal grain is shipped to the brewery and stored in silos. Barley, malted wheat or corn is crushed into fairly large particles.
*The malted grains are obtained from a conversion process called malting. The barley or wheat is first cleaned and then soaked to allow swelling. The grain is left to germinate for a time until the process is halted by kilning where the grain is subjected to high temperatures.

Illustration de Bruno Laporte

© Armand-Frappier Museum, 2008. All rights reserved.


The crushed grain is mixed with hot water in the mash tub, so called because of the mash formed by this mixture. The brewers keep a careful watch over the temperature of this mash to ensure the activation of the natural enzymes of the malt. These break down the starch into fermentable sugars (the most important being maltose) and the proteins into amino acids. The resulting distilled brew provides an ideal medium in which yeast grows very rapidly.

Illustration by Bruno Laporte

© Armand-Frappier Museum, 2008. All rights reserved.


In the lauter tub, the mash is first decanted and then filtered to remove residues such as grain husks, which might still be present.

Illustration by Bruno Laporte

© Armand-Frappier Museum, 2008. All rights reserved.


Beer is the only drink in the world that is boiled. The wort is brought to the boiling point (100°C) for at least one hour which eliminates undesirable proteins, resulting in a sterilized wort. At this point the hops (the flower Humulus lupulus ) are added which give beer its distinctive bitter taste. The wort is allowed to cool so that the yeast, which will soon be added, will not die.

Illustration by Bruno Laporte

© Armand-Frappier Museum, 2008. All rights reserved.


One particular strain of Saccharomyces cerevisiae is used for fermenting at low temperatures (between 8 and 12°C). The leaven of this strain is used to inoculate the fermenter. The yeast slowly ferments the sugar contained in the wort for approximately two months until the density of the sugar is stabilized. The beer is then allowed to reach maturity in the cold, always in 100 000-liter fermenters. The Unibroue brewery in Chambly, Quebec, produces its U, U2 and Bolduc beers in this way.

Illustration by Bruno Laporte

© Armand-Frappier Museum, 2008. All rights reserved.


In these 5 000-liter fermenters that maintain a temperature of more than 20°C, a strain of Saccharomyces cerevisiae derived from the previously prepared yeast starter is added to the wort. The sugar level is usually stabilized after two weeks and the beer is left to mature.

Illustration by Bruno Laporte

© Armand-Frappier Museum, 2008. All rights reserved.


Bottling and packaging

Illustration by Bruno Laporte

© Armand-Frappier Museum, 2008. All rights reserved.


Have you ever eaten raw sausages?

It is possible to preserve and eat raw meat without having any ill effects. The technique for doing this is known as lactic acid fermentation, a process that allows lactic acid-producing microorganisms to reproduce in certain foods such as raw sausages. The acidity produced kills harmful microorganisms, gives a nice flavor, and increases the shelf life of the meat.

In several cases, lactic acid fermentation, salting and drying allows meat to be kept at room temperature without too many problems. But beware that the conditions of fermentation must be rigorously controlled, otherwise harmful bacteria can develop and have disastrous effects. This is why it is recommended to use commercially prepared bacterial cultures.

Have you ever eaten raw sausages?

It is possible to preserve and eat raw meat without having any ill effects. The technique for doing this is known as lactic acid fermentation, a process that allows lactic acid-producing microorganisms to reproduce in certain foods such as raw sausages. The acidity produced kills harmful microorganisms, gives a nice flavor, and increases the shelf life of the meat.

In several cases, lactic acid fermentation, salting and drying allows meat to be kept at room temperature without too many problems. But beware that the conditions of fermentation must be rigorously controlled, otherwise harmful bacteria can develop and have disastrous effects. This is why it is recommended to use commercially prepared bacterial cultures.


© Armand-Frappier Museum, 2008. All rights reserved.

To prepare fermented sausages, various combinations of spices, flavoring agents, salt, sugar, additives (nitrites/nitrates), and bacterial culture are mixed into the meat. Commercially prepared bacterial cultures generally contain lactobacilli such as Lactobacillus plantarum and sometimes micrococci such as Micrococcus varians or Staphylococcus carnosus.

Photo : Nicole Catellier

© Nicole Catellier, Cinémanima inc.


From cabbage to sauerkraut!

Cabbage is naturally covered with a whole community of microorganisms, as are all living organisms. It is a subset of these microorganisms that develop and allow cabbage to be converted to sauerkraut.

Addition of salt to the cabbage mixture

Salt kills the undesirable bacteria and liquifies the cabbage. Microbial growth of the ferment can then proceed as it feeds on the nutrients expelled from the cabbage.

Lactic bacteria, which live naturally on the surface of the cabbage, are the cause of a first fermentation, which gives off some aromas and produces a light acidification. During the second fermentation, acidification inhibits undesirable bacterial growth while allowing the sauerkraut to be preserved much longer than the cabbage itself!

From cabbage to sauerkraut!

Cabbage is naturally covered with a whole community of microorganisms, as are all living organisms. It is a subset of these microorganisms that develop and allow cabbage to be converted to sauerkraut.

Addition of salt to the cabbage mixture

Salt kills the undesirable bacteria and liquifies the cabbage. Microbial growth of the ferment can then proceed as it feeds on the nutrients expelled from the cabbage.

Lactic bacteria, which live naturally on the surface of the cabbage, are the cause of a first fermentation, which gives off some aromas and produces a light acidification. During the second fermentation, acidification inhibits undesirable bacterial growth while allowing the sauerkraut to be preserved much longer than the cabbage itself!


© Armand-Frappier Museum, 2008. All rights reserved.

Sauerkraut

Photo : Nicole Catellier

© Nicole Catellier, Cinémanima inc.


Learning Objectives

The learner will:
  • familiarize himself with the vocabulary used in microbiology;
  • explain the relationship between developments in imaging technology and the current understanding of the cell;
  • identify which microorganisms are infectious, how the immune system fights against them, and the reinforcements of modern medicine;
  • describe the benefits of microorganisms .

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