Zoom in on microorganisms


Beer makingMovie ClipMovie Clip
© Production Cinémanima inc. and Armand-Frappier Museum

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.

Preparation of the yeastZoomZoom
© Illustration : Bruno Laporte

Steps in the production of beer

1. Preparation of the yeast
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.

Shipping, storing, and crushing the grainZoomZoom
© Illustration : Bruno Laporte

2. Shipping, storing, and crushing the grain
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.

Making the mashZoomZoom
© Illustration : Bruno Laporte

3. Making the mash
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 : Bruno Laporte

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

Boiling the mixture and adding hopsZoomZoom
© Illustration : Bruno Laporte

5. Boiling the mixture and adding hops
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.

Low temperature fermentationZoomZoom
© Illustration : Bruno Laporte

6a. Low temperature fermenters
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.

High-temperature fermentationZoomZoom
© Illustration : Bruno Laporte

6b. High-temperature fermenters
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.

Bottling and packagingZoomZoom
© Illustration : Bruno Laporte

7. Bottling and packaging