The slick taste in beer can be attributed to a compound called diacetyl. As a sommelier and brewer, I have encountered this off-flavor numerous times and it is definitely something that can affect the overall quality and enjoyment of a beer.
Diacetyl is a natural byproduct of the fermentation process and is produced by yeast during fermentation. In small amounts, it can contribute to the flavor profile of certain beer styles, such as English ales and some lagers. In these styles, a subtle buttery note is desired and can even add complexity to the beer.
However, when diacetyl is present in excessive amounts, it becomes a flaw in the beer. At higher concentrations, it can be perceived as a strong butterscotch flavor and aroma, overpowering the other flavors in the beer. This can be quite off-putting to many beer drinkers and is generally considered a fault.
Not only does diacetyl affect the flavor of the beer, but it can also impact the mouthfeel. When present in high levels, diacetyl can create a slick or oily sensation in the mouth, leaving a residue that coats the palate. This texture can be quite unpleasant and can detract from the overall drinking experience.
One personal experience I had with diacetyl was when I brewed a batch of pale ale. Everything seemed to be going well during the fermentation process, but when it came time to taste the final product, there was a noticeable slickness to the beer. The flavor was dominated by a strong butterscotch note, which completely overwhelmed the other flavors I had intended for the beer. It was disappointing, to say the least, as I had put a lot of time and effort into brewing that batch.
To avoid diacetyl-related issues, brewers need to closely monitor their fermentation process. Diacetyl is typically produced during the early stages of fermentation, but it can be reabsorbed by the yeast later on. This process is known as diacetyl reduction, and it involves raising the temperature of the beer slightly towards the end of fermentation to encourage the yeast to consume diacetyl.
In addition, proper yeast health and pitching rates are crucial to minimizing diacetyl production. Underpitching or using unhealthy yeast can increase the likelihood of diacetyl becoming a problem in the beer. It's also important to ensure that the beer is given enough time to fully ferment and condition before packaging, as rushing the process can lead to diacetyl-related issues.
The slick taste in beer is often caused by diacetyl, a compound that can be produced during the fermentation process. While small amounts of diacetyl can contribute to certain beer styles, excessive levels can result in a strong butterscotch flavor and a slick mouthfeel. Brewers must carefully monitor their fermentation process and take steps to reduce diacetyl production to avoid this off-flavor.