Off flavor in beer

Beer is a complex beverage containing a myriad of flavor- and aroma-active compounds. Brewers strive to achieve an appropriate balance of desired characters, while avoiding off aromas and flavors. Many beer flaws are the result of unwanted fermentation flavors.

The well-known off-flavors are earthy flavor from water, staling flavor such as cardboard and aging flavor which might be involved in mashing and boiling process, hydrogen sulfide during the fermentation process, vicinal diketones during the conditioning process and light-struck character at the market.

Off-flavor in beer including:
*Acetaldehyde (green apple, rotten apple): Acetaldehyde is a naturally occurring chemical produced by yeast during fermentation. It is usually converted into Ethanol alcohol

*Butyric acid (baby vomit): Commonly produced by a bacterial infection developed during brewing, butyric acid can also arise from poor sanitation during packaging

*Diacetyl (buttered popcorn, rancid butter): Caused by the presence of polysaccharides (dextrins) in the beer that are not fermentable by the yeast. Medium length proteins also contribute to palate roundness

*Dimethyl sulfide (aka DMS; canned corn, cabbage): S-methyl methionine (SMM) is created during the malting process of grain and is later converted to DMS when heated

*Hydrogen sulfide (rotten eggs): Formed by amino acids methionine and cysteine in the malt and by certain yeast strains and bacteria, notably Zymononas, Pectinatus, and Megasphaera. Also formed by yeast autolysis

*Mercaptan (rotten vegetables, skunk): Light will degrade hop iso-alpha acids which then combine with sulphur compounds in the beer to produce 3-methyl-2-butene-1-thiol, or prenyl mercaptan. Other sulphur compounds also contribute to the overall lightstruck character

*Metallic (metal, blood): the most common source of metallic off-flavors in beer is contact with metal components in the brewery

*Oxidation (cardboard): Oxidation of beer and the alcohol components into trans-2-nonenal and other aldehydes
Off flavor in beer

Food off flavor

Human-food interactions impact food acceptance and thereby the nutritional status of individuals. It is often said that even a hungry person would not eat if the sensory aspect of the food is offensive.

Flavor is one of the most important sensory qualities of a food. The flavor of a food is determined by a complex mix of taste, aroma, chemical response and texture.

Identification of the compounds causing an off-flavor in food and accurate quantification is critical in assessing the potential safety risks of a product or ingredient. Even when the tainting compounds are not at a level that would cause a safety concern, off flavors can have a significant impact on the quality and consumers' acceptability of products.

Off-flavors are widely defined as unpleasant odors or tastes resulting from the natural deterioration of a food. Off-flavors can be triggered by the involatiles detected by taste, but the main chemicals involved are the volatiles involved in odor response.

It is an atypical odor or taste may be due to incidental contamination of the food from environmental sources (e.g., airborne‐, waterborne‐, or packaging‐related chemicals) or may arise in the food itself (e.g., lipid oxidation, non-enzymatic browning or enzymatic action).

The oxidation can be enzymatic or nonenzymatic. Furthermore, off-flavors can be formed by the effect of heat on sugars and amino acids, such as Maillard reactions, by thermal degradation of phenolic acids, by oxidative and thermal degradation of carotenoids, and by thermal degradation of thiamine, or they can be derived as contaminants after solvent extraction.
Food off flavor