For thousands of years, people have been using the yeast Saccharomyces cerevisiae to ferment alcoholic beverages without even realizing it. It wasn't until 1680 when Dutch scientist Anton Van Leeuwenhoek observed these mighty cells for the first time under the microscope. It took another 177 years before the French scientist Louis Pasteur discovered and informed the world that yeast was alive and responsible for converting sugar to alcohol. Later on, in the late 1800s, Danish scientist Emil Christian Hansen was the first to isolate pure cultures of yeast.

Yeast under a Microscope (c) Lallemand Inc. 2023

The discovery of different strains of yeast led to the classification of brewer's yeasts into two categories: ales and lagers. Ale strains are top-fermenting, which means they ferment at higher temperatures and produce fruity beers. Lager strains are bottom-fermenting, which favors lower temperatures and produces a crisper, cleaner, and less fruity beer. The terms top or bottom-fermenting came about because ale yeast tends to clump and float to the surface at a point in the fermentation process, whereas lager yeast tends to settle to the bottom.

Yeast growing in a Petri dish (c) Lallemand Inc. 2023

If you're a beginner brewer, you might wonder how to choose the right yeast for your beer. You can buy ready-to-pitch yeast in dry or liquid form from manufacturers like Lallemand, depending on your brewing needs. Dry yeast offers a practical alternative to liquid yeast for microbrewers because it can be stored for over a year and is always ready to use whenever you're ready to brew. Liquid yeast, on the other hand, does not maintain viability over a long period and needs to be used within a few days, which impacts the flexibility of the brewing schedule. However, a greater selection of strains is available in liquid form. Both liquid and dry yeast can be recycled.

The quality of the yeast will have a significant impact on the outcome of the final product and as such should be treated with care and looked after. Any changes in the integrity or health of the yeast may impact the characteristics of the beer. Yeast maintenance is critical for the quality of the beer, and any brewery that practices yeast propagation can either keep their yeast stock on-site or order them regularly from an outside banking company. Even if using on-site stocks, it is recommended to keep a backup in an outside banking company in case of problems.


Dry Yeast. (c) Lallemand Inc. 2023

Yeast propagation encourages yeast growth rather than the production of alcohol. Propagation should occur in sterile wort in the presence of oxygen. Nutrition can be added, and particular attention should be paid to zinc levels. The temperature should be between 68-77°F to avoid a stressful environment, especially for lager strains. Most importantly, propagation should occur in several increments, with the Siebel Institute of Technology recommending eight-fold increments. As an example, starting with some yeast colonies from a plate, 10ml of wort is inoculated, and the process continues.

The pitching rate for brewer's yeast will depend on the original gravity of the wort to be inoculated. The right pitching rate will help ensure that the yeast is healthy, active, and ready to convert sugar to alcohol. It is always essential to follow the recommended pitching rate for the type of yeast you're using to avoid under-pitching or over-pitching. Under-pitching can result in poor fermentation, while over-pitching can lead to off-flavors in the beer.

In summary, yeast plays a crucial role in the brewing process. Choosing the right yeast, maintaining its quality, and propagating it correctly are all essential steps in brewing delicious beer. With proper care and attention to detail, you can produce high-quality beer.

Pitching Yeast. (c) Lallemand Inc. 2023

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