in broadest terms, refer to any attribute found in beer that was not intended by the brewer. It is imperative to understand that faults are not necessarily dictated by sensory preference or even stylistic guidelines, but rather are deviations from a standard developed by the brewer. When discussing faults, context is fundamental; a characteristic considered normal and essential for one beer may be appalling in another. The horsey, barnyard flavors evolved from Brettanomyces may be beguiling as part of a Belgian gueuze, but less so in an American mass-market lager.

Faults can be broken down into two general categories: those derived during the brewing process and those resulting postpackaging. These groups can then be subcategorized into sensory or physical defects.

To assure consistency, product specifications are established for every beer by identifying critical control points throughout the brewing process. Once a control point is identified, a target value is set along with an operating range (normally three standard deviations). Detailed analysis is performed on control points utilizing myriad instrumentation and human methods. Common faults originating in the brewery include bacterial spoilage, ingredient variation, haze, and improper carbonation level.

Bacterial spoilage is perhaps the most feared of beer faults, especially for nonpasteurizing breweries. Ironically, the cooked, oxidized flavor that can be imparted by pasteurization is also often considered a fault. Brewers thoroughly clean and sanitize all equipment that contacts beer to reduce the possibility of contamination. Sanitation is crucial during the entire process, but especially after wort cooling, when wort and beer temperatures are ideal for bacterial growth. Chemical sanitizers, if used improperly, can taint finished beer, so very hot water is often used. Lactobacillus, pediococcus, and acetobacter are common spoilage organisms that can impart sour, tart, buttery, and vinegar- like notes. See acetic acid bacteria, lactobacillus, and pediococcus. They are considered acceptable or desirable in sour beer styles, but not in most others.

Ingredient variance is a major concern for brewers. Beer is comprised of four main ingredients: malted barley (and/or other grains), hops, yeast, and water. Year-to-year barley and hop growing conditions, changes in the water supply, or poor yeast health will result in inconsistent raw materials for brewing. These differences can result in changes in color, hop bitterness and flavor, aroma, mouthfeel, and alcohol content.

Some faults are not olfactory or sensory, but rather, visual. The adage “you taste with your eyes” applies to beer haze. Haze is any cloudiness present in the beer at normal consumption temperature and can be caused by protein–polyphenol complexes, yeast, residual diatomaceous earth DE, or bacterial infection. Filtration, clarifying agents, and centrifugation are employed to reduce these hazes, but beer must be properly aged for optimal quality. The absence of haze can also be considered a fault when discussing certain beer styles that the consumer expects will be served cloudy (e.g., hefeweizen). Improper color is another visual fault. For example, the color of traditional pilsner beer may be pale gold to deep gold, but should not display reddish amber tinges.

Carbonation plays a significant role in beer not only in appearance and head retention but also in flavor presentation. Naturally carbonated beer relies on yeast to produce the proper level of carbonation, whereas forced carbonation uses high-pressure CO2 mechanically dissolved into solution. Undercarbonated beer will be flat tasting and have difficulty forming and holding a significant head. Overcarbonated beer may result in gushing and will taste harsh, and the “burn” of the CO2 content will drown out the more subtle flavors in the beer. Again, this is a matter of the expectations of the brewer and consumer. A Belgian saison will usually have a very high, Champagne-like carbonation, whereas British cask-conditioned beers should have a brisk tickle of CO2 on the palate.

Breweries utilize many practices to assure beer quality, perhaps none as vital as sensory analysis. All sensory analysis revolves around the taste panel. Panelists are selected by their ability to identify flavors and aromas. Because individuals have unique sensitivities and genetic blind spots, sensory scientists must develop and train panelists thoroughly before data become relevant. Panels are conducted in isolated rooms with noise and aroma dampeners. Red lights are often used to hide color differences. Sensory assessments are described as difference or descriptive tests. Difference tests ask whether one sample is different from another and include the triangle test, paired comparison test, and the duo–trio test. Descriptive methodologies require more training and often rank attributes on a scale. Trueness to type tests ask respondents to rank attributes of a sample compared with a known standard. All sensory data are statistically analyzed, often using complex software programs.

Breweries strive to put the best possible beer into package, only to face the inevitable assault of aging. The three biggest causes of faults in packaged beer are sunlight, heat, and oxygen. Light below 550 nm in wavelength causes the breakdown of hop iso- alpha acid molecules, resulting in sunstruck or lightstruck beer. See lightstruck. This skunky flavor and aroma is detectable at concentrations as low as 0.1 part per billion (ppb). Heat and oxygen promote oxidized flavors, perhaps the leading fault in beer in market. Good producers will provide “best by” dates so the consumer can avoid beer that may be past its prime. Packaging methods aim to keep oxygen levels below 80 ppb in the finished product to maximize shelf life, but low levels only slow the aging process; heat speeds the reaction. Oxidized characters are described as papery, cardboard, and vegetal. However, some beer styles are meant to age, and in those, slow oxidation can produce sherry-like flavors that are considered highly desirable, although they would not be accepted in a younger beer.