Krausen is a joyful moment in brewing and fermenting. When krausen appears, fermentation is under way. When it falls, fermentation is fertig (done). Knowing the subtle secrets of kräusen can greatly enhance brews.
A German verb, kräusen (pron. kroy-sen) means "to curl" or "to ruffle". In brewing it means "to condition (beer) by adding fermenting wort, so as to restart fermentation and introduce fresh carbon dioxide".
Krausen is the English noun. Formed during fermentation, it represents a critical phase. The layer of foam and bubbles is both a visual spectacle and happy indicator of active and hearty fermentation.
Krausen is created by top-fermenting yeasts such as Saccharomyces cerevisiae, also known as baker's or brewer's yeast. They're used to brew beverages like stout, ale, porter and Altbier, a copper colored brew popular in the German Rhineland.
Bottom-fermenting yeasts are preferred for lagers. These include Dortmunder, Pilsner and Bock, a strong dark beer brewed in fall to be consumed in spring.
Top-fermenting yeast creates a heady layer of foam on top of the brew during the vigorous stage of high krausen or hohe kräusen. It happens at the start of primary fermentation.
A mix of proteins, yeast and CO2 bubbles produced by the yeast, krausen appears as a thick, frothy layer ranging in hue from white to beige or light brown, depending on the ingredients used and type of beer being brewed.
Formation of Kräusen
Yeast Activation:
Pitching is the process of adding yeast to wort to start fermentation. When yeast is pitched into the wort it enters a phase of active reproduction and metabolism. The yeast cells begin to consume sugars in the wort, producing alcohol and carbon dioxide as byproducts.
Initially, the yeast multiplies by budding to form new cells. As these feed on sugars, their excretion of CO2 adds to the creation of bubbly foam rising to the top of the fermenter. The thickness and duration of krausen can vary based on several factors.
These include yeast strain, fermentation temperature and ingredients used in the wort. Some yeast strains may produce krausen for only a couple of days, while others create a robust foam prevailing for over a week.
Protein Interaction
The proteins present in the wort influence krausen formation. As CO2 bubbles rise, they trap some of the proteins, creating a stable foam. This protein structure is crucial for the foam's longevity and contributes to the beer texture.
Temperature and Fermentation Dynamics:
The temperature of fermentation can significantly influence krausen formation. Warmer fermentation temperatures typically result in a more vigorous fermentation, leading to a larger and denser krausen. Cooler temperatures may produce less krausen.
While yeast can grow in various conditions it's most prolific at temperatures of 32˚C-35˚C (90˚F-95˚F) and pH of 5.5, slightly acidic. Higher heat inhibits yeast growth. The thermal death point for yeast is 55° - 60° C (130° -140° F). If cooled, it stops activity at 40° F (4° C).
Yeasts have the ability to produce antimicrobial compounds to inhibit growth of harmful mold or bacteria. If yeast and mold have a battle on even turf, yeast will probably win. Copper equipment is also known to repel viruses and bacteria, therefore commonly used in brewing.
If beer or mead forms unwanted krausen, the layer can be skimmed off the top. Brewers might do this if the krausen tastes bad rather than imparting its flavors into the booze, especially if they have a certain flavor profile in mind.
Significance of Krausen
Indicator of Fermentation
The presence and characteristics of krausen serve as a visual cue for brewers to gauge fermentation activity. The presence of krausen clearly shows fermentation is happening.
For brewers, seeing krausen is a reassuring sign that the yeast is healthy and working properly. A vigorous krausen indicates healthy yeast activity, while a lack of krausen can signal problems such as under-pitching of yeast or temperature problems.
A potential problem is the overdevelopment of yeast into a killer strain. This can destroy beverage flavors. When yeast is under pressure by competition it can release a toxin to kill other strains or even weak members of its own strain. The toxins also kill beer.
Flavor Development
During fermentation, yeast contributes various flavor compounds. These include esters and phenols, which can influence the taste profile of the beer.
Krausen contains these flavor precursors, making it integral to the beer’s aroma and taste. It helps create esters for provide fruity notes and phenolic compounds for spiciness.
Impact on Beer Clarity
After fermentation is complete, the krausen eventually subsides, and proteins and other particles settle out of the beer. This sedimentation process is essential for achieving clarity in the final product.
Hygienic Considerations
Krausen can also serve as a barrier against contaminants. The foam layer helps seal the fermentation vessel, reducing the risk of unwanted microbial intrusion. However, excessive krausen can lead to blow-off, where foam spills over the top of the fermentation vessel.
The barrier krausen creates is a defense against airborne contaminants. This protection is crucial, as it minimizes exposure to unwanted wild yeast and bacteria.
Temperature Regulation
Krausen has insulating properties to help maintain a stable fermentation temperature. Yeast produces biofilms to cultivate the environment it loves. Controlled temperature prevents yeasts from overheating, which is essential for a successful fermentation process.
Managing Krausen in Fermentation
While krausen is an exciting feature of fermentation, managing it is crucial to prevent issues like overflow. Here are a few practical tips for handling krausen effectively:
Positioning the Fermenter: Put the fermenter in an area with space for possible overflow. Using a blow-off tube can effectively release excess gas during intense fermentation.
Understanding Yeast Characteristics: Different yeast strains create various amounts of krausen. For instance, German Weissbier yeast typically produces a large krausen, whereas a clean ale yeast may generate significantly less.
Managing krausen is integral to the fermentation process. When krausen starts to decrease, it's time for racking to secondary fermentation or preparation for bottling.
The beer head is created by the carbon dioxide bubbles earlier released by the yeast. A thick head indicates well-nourished yeast. Some brewers add yeast-fortifying proteins and nutrients especially made for these industrious microbes.
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