View Cart Checkout. Toggle navigation. Starter Kits. Kegerator Conversion Kits Homebrew Commercial. Sake Making. Food Processing Equipment Ingredients. Bar Tools. New Products. Diacetyl — the compound responsible for buttery or butterscotch flavors that sometimes arise in beer — can be controlled if you understand the mechanisms that contribute to its production. Diacetyl and 2,3-pentanedione are important contributors to beer flavor and aroma.
Organic chemists classify both as ketones, and diacetyl is usually called 2,3-butanedione in the literature. Sometimes these two ketones are grouped and reported as the vicinal diketone VDK content of beer. A report, for example, stated that the average diacetyl level of American commercial beer was 0. Today the average is near 0. Some notable exceptions exist. Some stouts can have levels as high as 0.
Diacetyl levels in beers brewed by microbreweries and brewpubs tend to vary considerably, ranging from 0. The presence of diacetyl is usually indicated by a buttery or butterscotch tone. In fresh beer the flavor can be confused with that of caramel malts. Given time it is easy to distinguish the two; diacetyl tends to be unstable in most beers and can take on raunchy notes.
The flavoring imparted by caramel malts, on the other hand, tends to be stable. The flavor threshold of 2,3-pentanedione is near 1. This compound can be found well above threshold levels in sonic Belgian ales, where it is considered a natural flavor constituent for this style. It occurs less often in other beer styles and is regarded as a defect.
Using microscopy, Pasteur found that what we know today as lactic acid bacteria were responsible for many off-flavors in beer. The term sarcina sickness is used to describe this effect. Apparently, the involvement of diacetyl in sarcina sickness was discovered early, but it was not until that Shimwell linked this compound with the taste and smell of butter. Earlier studies got the organic chemistry right but were wide of the mark in terms of flavor chemistry.
During the early period, the only known mechanism of diacetyl formation was bacterial infection caused by unsanitary conditions. Practical brewers believed that some other factor must be involved, because buttery tones occasionally showed up in beer brewed in impeccably clean environments. Major breakthroughs occurred during the s and early s.
Owades developed an effective technique for measuring diacetyl and used this method to study the fate of the compound in brewing. Necrosis of nasal and airway epithelium in rats inhaling vapors of artificial butter flavoring. Toxicol Appl Pharmacol 2 — Hubbs, A. The American journal of pathology, , Respiratory toxicologic pathology of inhaled diacetyl in Sprague-Dawley rats.
Toxicol Pathol 36 2 — Airway epithelial toxicity of the flavoring agent, 2,3-pentanedione. Respiratory and olfactory cytotoxicity of inhaled 2,3-pentanedione in Sprague-Dawley rats. Am J Pathol 3 Toxicol Sci 1 — Morgan, D. Toxicol Pathol, 44, Morris, J. Inhalation dosimetry of diacetyl and butyric acid, two components of butter flavoring vapors. Toxicol Sci, , — Skip directly to site content Skip directly to page options Skip directly to A-Z link.
It is this conversion that provides the main source of diacetyl in beer. Some of this ester is used by the cell to produce the amino acid valine, but most is dumped into your beer. Oxygen and high temperatures help transform this into diacetyl. The amount of diacetyl wanted varies from the type of beverage being brewed and if taken, the next step helps determine this. After fermentation, the yeast will reabsorb as much or as little diacetyl intended.
Often this is referred to as a " diacetyl rest ," in which high temperatures, and allowing the beer to remain in the fermenter after fermentation, will cause the yeast to reabsorb excess diacetyl and break it down.
Diacetyl also may be found in homes through the vapor that occurs when a bag of finished microwave popcorn is opened.
Worker inhalation of diacetyl through flavoring volatiles has generated concern. Diacetyl is under scrutiny in the European Union EU , however EU is waiting for more data before developing standards. Diacetyl has been linked to the lung disease bronchiolitis obliterans, especially in occupations that involve the manufacturing or use of certain artificial butter flavorings.
NIOSH recommends the following steps to industry for worker safety: personal protective equipment, worker education to increase awareness, symptom reporting, proper ventilation design, and the use of substitute products to reduce risk.
Since, flavoring generally has many chemicals—not just diacetyl— substitutes providing the same diacetyl function may or may not reduce the risk of lung disease; more research is needed. Although NIOSH does not anticipate significant risk to normal consumers of microwave popcorn, based on limited available data, it is suggested that consumers use proper ventilation and wait for the microwave popcorn to cool.
NIOSH developed protective guidelines for workers, who may be exposed to diacetyl through inhaling flavoring vapors at a food facility. Although it is not anticipated that consumers are at risk from normal consumption of food products that contain diacetyl, food manufacturers are taking steps to find safer alternatives.
A strong food safety culture is not dependent on one element.
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