Brettanomyces lambicus is a type of yeast that occupies a unique and controversial position in the world of fermented beverages. This microorganism is simultaneously sought after by certain artisan producers and aggressively avoided by others. Its ability to dramatically alter the flavor profile means its presence can signify intended complexity or disastrous spoilage. Whether this organism is harmful or helpful depends entirely on the context and the desired final product.
Defining Brettanomyces lambicus
Brettanomyces lambicus is classified as a non-Saccharomyces yeast, distinguishing it from the common strains used in modern brewing and winemaking. In the wild, this microorganism naturally inhabits the skins of fruits and porous surfaces of wood, such as oak barrels. It is often colloquially referred to simply as “Brett” and is known for its distinct and slow metabolic processes.
A key characteristic of this yeast is its ability to produce specific volatile phenolic compounds from precursors like cinnamic acids found in the liquid. The two most prominent are 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG). When exposed to oxygen, B. lambicus is also acidogenic, meaning it can produce acetic acid, which contributes a vinegary note.
The Beneficial Applications in Fermentation
The intentional use of B. lambicus is rooted in traditional brewing, particularly in Belgium, where its unique flavor contributions are signature characteristics. It is indispensable to the production of authentic Lambic beers and their derivatives, such as Gueuze, which rely on spontaneous fermentation. In these styles, the yeast’s slow action is cultivated over months or even years.
The flavors produced by B. lambicus are often described positively as earthy, barnyard, or leathery, adding significant depth and complexity. A small concentration of 4-EG, for instance, can introduce pleasant notes of clove or smoke. The yeast also metabolizes residual, complex sugars that standard Saccharomyces yeast cannot consume. This secondary fermentation results in a highly attenuated, or very dry, finished product, a quality prized in these traditional sour beer styles.
The Detrimental Effects and Spoilage
Outside of specific traditional styles, Brettanomyces lambicus is overwhelmingly regarded as a spoilage organism, particularly in commercial winemaking and conventional brewing. The production of 4-ethylphenol (4-EP) is the primary cause of this negative reputation, as this compound imparts strong, undesirable aromas. These off-flavors are commonly described as medicinal, Band-Aid, or horse stable, ruining the clean profile expected in most wines and mainstream beers. The sensory threshold for 4-EP is low, meaning even a small presence of the yeast can lead to noticeable spoilage.
This organism is notorious for its resilience, being highly tolerant of low pH environments, alcohol, and the sulfur dioxide (SO2) levels used for microbial control. This resistance makes it a persistent and difficult contaminant to eliminate from winery and brewery equipment. Economically, B. lambicus poses a serious threat, potentially damaging a significant portion of the world’s red wine production. Costs involve product loss through dumping, extensive sanitation efforts, and the downgrading of infected batches to lower-value blends.
Health and Consumption Safety
Despite its significant impact on product quality, Brettanomyces lambicus is not considered a threat to human health for the average consumer. The “harm” associated with the organism relates overwhelmingly to the sensory and economic spoilage of fermented products. It is classified as non-pathogenic, meaning it does not cause disease in healthy individuals who consume beverages containing it.
The yeast and its metabolic byproducts are consumed regularly in traditional styles like Lambic without adverse health effects. However, consumption by individuals who are severely immunocompromised or have underlying health conditions should be approached with caution. These individuals are advised to consult a physician regarding the consumption of any live yeast or bacteria.