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Guide to beer off-flavors light-struck

Guide to beer off-flavors: Light-struck

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.
Guide to beer off-flavors: Light-struck

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

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.
beer keg

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. In addition, this is also the thirteenth article of our beer off-flavor guide. You can check our previous articles to learn more about beer off-flavor and know how to deal with off-flavor.
Guide to beer off-flavors acetic acid
Guide to beer off-flavors: Acetic acid

No matter how many times you have brewed beer in the past when you open the first bottle of a new batch, it is always exciting. Maybe the aroma of hops will be as good as expected, maybe the beer will be muddy, or the beer will taste like vinegar. Beer that tastes like vinegar

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Guide to beer off-flavors phenolics
Guide to beer off-flavors: Phenolics

Beer always contains some form of phenols (phenols and polyphenols, etc.), such as tannins (directly derived from hops and malt). Although low levels of polyphenols can increase the taste of beer, high levels of polyphenols can cause dryness and astringency. When beer glasses are described as phenols, they usually refer to volatile phenols. Volatile phenols

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Beer off-flavor guide chlorophenol
Beer off-flavor guide: Chlorophenol

Have you ever tried a beer that smells of medicine and tastes like band-aids? If so, it is because the beer contains chlorophenol. Chlorophenol can give the beer a plastic taste, smoke, chlorine disinfectant, or band-aid taste. Next, the brewer of Micet Craft will explain the source of chlorophenol and how to reduce the content

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Guide to beer off-flavors Metallic
Guide to beer off-flavors: Metallic

It is not normal for Metallic to appear in any flavored beer. If you can taste Metallic or bloody taste in beer, it is recommended not to drink this beer. Under normal circumstances, the source of iron ions is only a very small amount of iron-containing protein in grains, which will enter the beer during

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Guide to beer off-flavors Alcoholic
Guide to beer off-flavors: Alcoholic

Some craft beer will produce excessive alcohol taste and aroma. This can vary from a slight alcoholic warmth to strong alcohol that tastes like moonshine. Next, Micet Craft will explore the root cause of the alcoholic odor. In addition, this is also the eighth article about beer’s peculiar smell. If you are interested, you can

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Guide to beer off-flavors hydrogen sulfide
Guide to beer off-flavors: hydrogen sulfide

The presence of hydrogen sulfide (H2S) in beer will give the beer a unique smell of rotten eggs. In some beer styles, a small amount of hydrogen sulfide will form a unique flavor in the beer. But, if beer contains more hydrogen sulfide, the beer may produce a pungent rotten egg flavor, which is not

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Guide to beer off-flavors acetaldehyde
Guide to beer off-flavors: acetaldehyde

The peculiar smell in beer has always been a headache for brewers, although some peculiar smells are characteristic in some beer styles. But acetaldehyde is a special taste, because it may cause you to have a hangover, which is very detrimental to your health. Next, Micet Craft will introduce you to acetaldehyde-related content, so that

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Guide to beer off-flavors DMS
Guide to beer off-flavors: DMS

One of the most frequently mentioned odors in beer evaluation is dimethyl sulfide (DMS). DMS is a sulfur compound that is generally thought to give beer creamed corn or cooked vegetable characteristics. Most beer brewers know very well how to reduce the risk of DMS entering the beer, such as checking the boiling time and

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Guide to beer off-flavors infection
Guide to beer off-flavors: infection

Is my beer infected? This is a question we often receive. Next, Micet Craft will introduce the content of beer infection. This is also the fourth article in our beer off-flavors series. If you are interested, you can read other articles related to odor. We hope to help you better complete beer brewing. Guide to beer

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Guide to beer off-flavors: isoamyl acetate

The most important ester found in beer is isoamyl acetate, which has a flavor like rubber or pear blossom. Isoamyl acetate is considered an ester, or a mixture of alcohol and acid. Because fermentation (yeast converting sugar into alcohol) produces isoamyl acetate, isoamyl acetate is a very common off-flavors in all beer. Although the content

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Guide to beer off-flavors acetic acid
Guide to beer off-flavors: Acetic acid

No matter how many times you have brewed beer in the past when you open the first bottle of a new batch, it is always exciting. Maybe the aroma of hops will be as good as expected, maybe the beer will be muddy, or the beer will taste like vinegar. Beer that tastes like vinegar

Read More »
Guide to beer off-flavors phenolics
Guide to beer off-flavors: Phenolics

Beer always contains some form of phenols (phenols and polyphenols, etc.), such as tannins (directly derived from hops and malt). Although low levels of polyphenols can increase the taste of beer, high levels of polyphenols can cause dryness and astringency. When beer glasses are described as phenols, they usually refer to volatile phenols. Volatile phenols

Read More »
Beer off-flavor guide chlorophenol
Beer off-flavor guide: Chlorophenol

Have you ever tried a beer that smells of medicine and tastes like band-aids? If so, it is because the beer contains chlorophenol. Chlorophenol can give the beer a plastic taste, smoke, chlorine disinfectant, or band-aid taste. Next, the brewer of Micet Craft will explain the source of chlorophenol and how to reduce the content

Read More »
Guide to beer off-flavors Metallic
Guide to beer off-flavors: Metallic

It is not normal for Metallic to appear in any flavored beer. If you can taste Metallic or bloody taste in beer, it is recommended not to drink this beer. Under normal circumstances, the source of iron ions is only a very small amount of iron-containing protein in grains, which will enter the beer during

Read More »
Guide to beer off-flavors Alcoholic
Guide to beer off-flavors: Alcoholic

Some craft beer will produce excessive alcohol taste and aroma. This can vary from a slight alcoholic warmth to strong alcohol that tastes like moonshine. Next, Micet Craft will explore the root cause of the alcoholic odor. In addition, this is also the eighth article about beer’s peculiar smell. If you are interested, you can

Read More »
Guide to beer off-flavors hydrogen sulfide
Guide to beer off-flavors: hydrogen sulfide

The presence of hydrogen sulfide (H2S) in beer will give the beer a unique smell of rotten eggs. In some beer styles, a small amount of hydrogen sulfide will form a unique flavor in the beer. But, if beer contains more hydrogen sulfide, the beer may produce a pungent rotten egg flavor, which is not

Read More »
Guide to beer off-flavors acetaldehyde
Guide to beer off-flavors: acetaldehyde

The peculiar smell in beer has always been a headache for brewers, although some peculiar smells are characteristic in some beer styles. But acetaldehyde is a special taste, because it may cause you to have a hangover, which is very detrimental to your health. Next, Micet Craft will introduce you to acetaldehyde-related content, so that

Read More »
Guide to beer off-flavors DMS
Guide to beer off-flavors: DMS

One of the most frequently mentioned odors in beer evaluation is dimethyl sulfide (DMS). DMS is a sulfur compound that is generally thought to give beer creamed corn or cooked vegetable characteristics. Most beer brewers know very well how to reduce the risk of DMS entering the beer, such as checking the boiling time and

Read More »
Guide to beer off-flavors infection
Guide to beer off-flavors: infection

Is my beer infected? This is a question we often receive. Next, Micet Craft will introduce the content of beer infection. This is also the fourth article in our beer off-flavors series. If you are interested, you can read other articles related to odor. We hope to help you better complete beer brewing. Guide to beer

Read More »
craft beer
Guide to beer off-flavors: isoamyl acetate

The most important ester found in beer is isoamyl acetate, which has a flavor like rubber or pear blossom. Isoamyl acetate is considered an ester, or a mixture of alcohol and acid. Because fermentation (yeast converting sugar into alcohol) produces isoamyl acetate, isoamyl acetate is a very common off-flavors in all beer. Although the content

Read More »
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