BFA - Yeast Propagation

The value of a good yeast propagation system can not easily be calculated in figures, it is often only recognised when problems occur. Breweries that routinely use harvested or cropped Yeast for Yeast Pitching are well aware that the quality and the physiology of the yeast diminishes with each pitching. Changes in the genome of the yeast may occur and the risk of contamination (Lactobacillus sp.; Pediococcus damnosus, etc.) increases and changes of the quality of the packaged beer can take place. The fermentation may slow down, resulting in longer fermentation and maturation times including attenuation difficulties or the fermentation may even stop (hung fermentation).

Yeast propagation systems are used which enable fresh, pure yeast culture to be pitched regularly, to avoid the problems associated with yeast of too many generations. A generation of yeast refers to the number of fermentation cycles the yeast has undergone. Normally 5 to 10 (max) generations are used before a fresh, pure yeast culture is pitched.

Types of Aerobic Yeast Propagation Systems

There are two primary types of aerobic yeast propagation systems in use today, namely: the continuous yeast propagation (originally called Conti-Prop by Esau & Hueber GmbH and the name has stuck), and batch yeast propagation. Both types are very similar by nature and design. The main differences are:

It is important to note that our yeast propagation plants can be used as batch or continuous propagation plants.

Esau & Hueber's Aerobic Yeast Propagation System

Our Aerobic Yeast Propagation Systems are designed to ensure that the yeast gets enough oxygen throughout the whole propagation. Gaining the most available energy from each molecule of glucose, also the synthesis of unsaturated fatty acids and sterols is guaranteed, as both are essential membrane components.

If lager and-or ale yeast is propagated under aerobic conditions the cell contains active mitochondria (-cell power plants-) with an active respiration chain for the synthesis of energy. Only through these conditions is the yeast cell able to gain 38 ATP from each molecule of glucose, compared to only 2 ATP per molecule of glucose during fermentation.

The high energy generated through the respiration chain enables strong cell proliferation. The steady, controlled cell growth reduces the chance of mutation of the yeast with the new cells showing high vitality and high viability ( dead cells <1%). This is important especially for continuous propagation systems because need to replace staring yeast culture is much less frequent than in old systems of this type.

With the yeast being so healthy and vital, resistance to infection and any contamination in the propagator as well as in the fermentation cellars is seriously reduced. The high vitality of the yeast ensures high yeast proliferation during yeast pitching and within the first few hours of fermentation, resulting in a fast start of the fermentation and a fast reduction of the extract. The decline of the pH to values below 4.5 reduces the risk of any contamination.
Harvesting or cropping this yeast from the fermenter allows the reuse of this active yeast in the brewery, or the excess yeast can be sold to other breweries or yeast extract factories.

When brewing, for example, a classic Bavarian wheat-beer, that is bottle fermented, this yeast can also be used for the second fermentation in the bottle. The high vitality reduces the chance of autolysis and the chance of agglutination of the yeast. So a quick, steady second fermentation (in the bottle) is guaranteed, as well as an intensely smooth wheat-beer flavour. There will be no flocculation of the yeast during the dispensing of the beer from the bottle. With this yeast fermentation in the bottle the danger of infection or contamination of the product is reduced.

The propagated yeast can be adjusted to match the brewing schedule through:

These parameters can be varied to adjust the yeast propagation system to the needs of your brewery. If some changes occur during the propagation you are able to change any of the parameter during the propagation process, if necessary. This type of yeast propagation system offers the highest flexibility, to meet the demands of your brewhouse, enabling easy handling of the changes in demand for yeast, in peak and low season. Due to the system flexibility it is possible to use this yeast propagation system for your normal yeast as well as for any other-or special-yeast strains required for different beers.

Brewery Yeast Propagation

Types of Aerobic Yeast Propagation Systems

Esau & Hueber's Aerobic Yeast Propagation System