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Beer Odor Guide: Light-struck

Views: 9     Author: Site Editor     Publish Time: 2022-10-08      Origin: Site

The most common odor in commercial beer and craft beer is the smelly “Light-struck” flavor and aroma. It can make your beer emit a strong smell (it feels like a skunk) and make it unpleasant to drink.

What Is Light-Struck?

When light hits the beer, the ultraviolet rays interact with hop compounds and produce MBT. This chemical is the same chemical that the skunk squirts, so you might think of the smell that the skunk emits. Humans can detect it under the aroma threshold of one part per billion. This kind of beer with a peculiar smell is called “skunked”. Also, the light-struck process can happen within a few seconds, so if you lie on the beach and enjoy beer, you may smell this smell.

Of course, if your beer is stored in opaque containers like kegs, cans, ceramic bottles, or stainless steel bottles, the taste will not change much. If your beer is stored in a green or transparent glass bottle, you need to be careful, the beer may have been Light-struck. Because transparent glass bottles cannot block any ultraviolet rays, green glass bottles can block about 20% of the ultraviolet rays, but 80% of the ultraviolet rays still enter the beer.

Why Is Beer Skunked?

Although most beer drinkers know the existence of “skunked”, they don’t know how it is produced. The hops used in brewing beer contain light-sensitive compounds. When these compounds are exposed to strong light, a photo-oxidation reaction occurs, producing a strong flavor-active compound 3-methyl-2-butene-1-thiol (known as MBT). MBT is one of the most powerful flavor substances known to man, and is often referred to as “skunked”. This pungent odor compound is like the infamous defensive spray used by skunks.

In 1875, German chemist Dr. Carl Lintner reported for the first time that beer exposed to light would form an unpleasant taste and smell. In 1960, Yoshiro Kuroiwa announced that the main component of the odor was MBT, which originated from the photolysis of isohumulones. In addition, the Kuroiwa team determined that the skunked taste would be more pronounced under the light in the blue part of the visible spectrum (350-500nm). Under strong sunlight, the reaction was almost instantaneous, and the tasting team could detect the presence of MBT in the beer exposed for less than 10 seconds. Under less harmful conditions, these reactions will still occur, but it can take days or even weeks to become apparent.

Light-Struck And Beer Bottle Types

In the real world, beer is affected by light with a wavelength between 400-500nm (the blue end of the spectrum) and ultraviolet rays with a wavelength less than 400nm. Brown beer bottles can cut the impact of light exposure on beer and block light below 500nm. In contrast, green beer bottles can only block ultraviolet rays below 400nm, while transparent bottles have almost no protection against Light-struck.

What Impact Did Light-Struck Have On The Choice Of Beer Bottles?

The odor-producing reaction involves the cleavage of the isopentenyl side chain of the iso-alpha acid in hops. This cleavage is photocatalytic and can lead to the formation of dimethylallyl radicals. Free radicals react with sulfur-containing compounds (thiols) to form MBT. The green and clear glass have little protection against this reaction, but brown glass is very effective (at least for short-term or low-intensity exposure). Try to transfer the beer to opaque kegs or cans to provide the best protection from light. Although transparent and green glass bottles lack protection for beer, some breweries still insist on using them. This is because the color of beer bottles has also become an important part of the brewery’s brand strategy.

When the beer bottle does not provide protection, modern hop science provides an alternative that can prevent the formation of MBT from hops. “Tetra” and “Hexa” hops are modified by reductions in side-chain double bonds that prevent the photodegradation reaction. These advanced hop products are based on liquid or supercritical carbon dioxide extracts of hops, See humulone. These resins will in turn be alkaline It is isomerized to humulone in the solution, and isohumulone can be further reduced to produce bitter compounds that will not degrade into MBT. This kind of bitter hops with an advanced form is called a “light-stable” product. They are used in the brewing process to make beer less susceptible to the harmful effects of sunlight. But, sunlight may also produce other flavor changes that are not related to hops.

How To Avoid Stinking Beer?

Avoiding stinking beer is very easy: just keep the beer from being exposed to light. The best way is to pack the beer in an opaque container, such as a keg. Commercial breweries can also use cans to package beer. If you can only use glass bottles to package beer, it is recommended to use brown glass bottles, which are more effective than green or clear glass in blocking harmful ultraviolet rays. But, even brown glass bottles cannot be 100% insulated from light, and the bottles still need to be stored in a dark place. For many home winemakers, glass bottles or light-transmitting jars may be used for fermentation or storage, which may also lead to the formation of off-flavors. It is best to cover them with a towel or black garbage bag and store them in the dark.

Of all the off-flavors that affect beer, the skunk is the easiest to avoid. These unpleasant off-flavors can be avoided only by proper packaging and storage.

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