Beer Odor Guide: 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 is because the acetic acid content in the beer is too high. Every brewer may have brewed inferior beer in the past. When this happens, you need to find the problem and prevent it from happening again.

What Is Acetic Acid?

Acetic acid is the acid contained in vinegar (3%-6%), and it is also the main volatile fatty acid in alcoholic beverages. Acetic acid is the main fatty acid produced by yeast metabolism and the key component of ethyl acetate (reaction with ethanol). Ethyl acetate is the most common flavor fat in beer. We will discuss this aspect in the follow-up content.

How To Recognize Acetic Acid?

A small amount of acetic acid does not have much effect on beer, because basically all beer contains a small amount of acetic acid. But if the content of acetic acid is too high, it will affect the flavor of the beer, making the beer taste like vinegar or apple cider vinegar.

Why Is Acetic Acid Produced?

Acetic acid is produced by yeast during the fermentation process and is a natural part of the brewing process. It can also be produced by wild yeast, which produces more acetic acid than other yeasts and will change the flavor characteristics of the beer. Extremely sour or vinegar smells are almost always the result of bacterial or wild yeast infections. Acetic acid can also be produced by bacteria consuming sugar and indicates that beer spoilage is more problematic.

Under normal circumstances, the acetic acid produced by the yeast strain will be below the flavor threshold. When acetic acid in beer is easy to identify, it is usually caused by acetic acid bacteria. Acetic acid bacteria can survive in ethanol, are acid resistant, and hop compounds do not affect it. Also, acetic acid bacteria are a kind of aerobic bacteria, if over-aeration, ethanol will be converted into acetic acid during the fermentation process. The oxidation process of acetaldehyde will also produce some acetic acid, which will produce a complex reaction of aroma during the beer maturation process.

If acetic acid is present in an amount higher than the perception threshold, acetic acid will bring the flavor and aroma of acetic acid to beer. But, this is usually not a problem in the correct brewing process. Because most beer is produced under strict quality control, pollution and oxidation will be minimized. Also, acetic acid is not a problem in properly packaged beer, because there is usually no oxygen in the packaged beer.

If the beer brewing process cannot be entered correctly, then excessive acetic acid may appear in the beer. Now, the beer may be destroyed due to the presence of excess acetic acid. So what causes an excess of acetic acid:

• Use wild yeast. Part of the wild yeast will produce a lot of acetic acid during the fermentation process, which is also the type of yeast used in the brewing of some sour beer.

• Beer is exposed to the air. The air contains a lot of acetic acid bacteria. If the beer is exposed to the air, acetic acid bacteria will enter the beer. And because the beer is exposed to the air, acetic acid bacteria will multiply or move in large numbers, so that the acetic acid content in the beer will increase rapidly. Of course, this is also the most common brewing method for brewing sour beer.

• The brewery equipment is not cleaned properly. Brewery equipment that is not properly cleaned and disinfected may leave bacteria in the previous batch of beer, contaminating the brewhouse and fermentation tanks. When beer enters the brewhouse and fermentation tanks, these bacteria will make the beer sour and may also cause the beer to deteriorate.

• Some air remains after the beer is packaged. As we mentioned above, acetic acid is a natural by-product in the beer brewing process, and acetic acid bacteria are aerobic bacteria. If some air remains in the beer bottle, it will allow acetic acid bacteria to convert ethanol into acetic acid.

• The oxidation process of acetaldehyde also produces acetic acid.

How To Avoid Excessive Acetic Acid?

When the previous batch of beer has a vinegar taste, we should avoid excessive acetic acid production in the next batch of beer. Under normal circumstances, we need to take the following measures to minimize the formation of acetic acid:

• Use proper yeast. You need to adjust the type of yeast according to the brewing process and try to avoid using wild yeast.

• Do not over-ventilate during the fermentation process. Hyperventilation allows acetic acid bacteria to quickly convert ethanol to acetic acid.

• Properly clean and disinfect brewery equipment. Use the correct cleaning agent and disinfectant to treat the equipment, and rinse the equipment with clean water after treatment to ensure that the equipment is clean and hygienic.

• When packaging beer, try not to leave air in the beer bottle.