Causes of Beer Defects

The main factors that cause beer odor are poor quality of raw materials, unreasonable process, contamination by harmful substances (such as contaminated water, moldy barley, residual cleaning agents and fungicides), microbial contamination in the production process, transportation, Poor storage and sales conditions, etc. Here are some reasons for common taste defects in beer for your reference.

 Unpleasant bitter taste 

Consumers often blame unpleasant bitterness in beer, which is mostly manifested as not delicate entrance, rough bitterness and bitterness afterward, mainly due to two factors: raw materials and craftsmanship.

1. Factors in raw materials

The residual alkalinity, total hardness, magnesium, iron, and manganese ions in the water are too high; the quality of the hops is poor, the hops have been aged after long-term storage, and the origin is not ideal;

Poor quality malt, such as rough husk and high protein and tannin content.

2. Process factors

Saccharification process: The saccharification and wort filtration time is long, so that excess tannins, anthocyanins and fatty acids enter the wort; the filtered wort is cloudy, and the wort enters too much oxygen during cutting, stirring and pouring. Phenol reacts with oxygen.

Fermentation and post-storage process: the separation effect of cold and hot coagulates is not good, the foam cap sinks and dissolves in the wine, the process pipeline grows mold, the post-storage temperature is too high, and more yeast enters the wine storage tank.

 Yeast flavor 

Yeast odor is an unpleasant odor and taste, especially when yeast autolyses. Yeast-flavored beers tend to be characterized by high pH, darker color and poor foam performance.

Causes of Brewer's Yeast Smell：

When the wine storage temperature is high and the wine storage time is too long, the yeast will autolyse and release fatty acids. Studies have shown that these substances can give beer an unpleasant off-flavor and adversely affect foam. High levels of ethyl acetate and ethyl laurate can work together to create a yeasty flavor, but one of them does not. works alone.

Hygiene issues such as mold growth in pipes can also contribute to the yeasty taste of beer.

 The green taste of beer 

The green taste of beer is generally described as an immature smell and taste. Reasons for the green taste of beer:

The green taste of beer is caused by the short post-fermentation time and unreasonable post-fermentation process. The odor-inducing substances are mainly sulfur-containing compounds and acetaldehyde with a high content. A series of volatile sulfides such as hydrogen sulfide, sulfur dioxide, dimethyl sulfide, methylthioenol and some low molecular mercaptans are produced during the fermentation process. The taste threshold for sulfur dioxide is 10-20mg/L, while the taste threshold for hydrogen sulfide is only 0.05-0.02mg/L. When dimethyl sulfide is not higher than 100ug/L, it is beneficial to the taste of beer, and mercaptans less than 10ug/L generally do not feel it.

Volatile sulfides can be separated by CO2 washing during fermentation. Generally, the amount remaining in beer is 0.5ug/L, which is lower than the taste threshold. The sulfur dioxide reached 20mg/L in the main fermentation, and then decreased again in the post-fermentation period. The content of dimethyl sulfide depends on the quality of malt, mashing method and boiling time, and is generally less than 100mg/L. The content of mercaptans decreased from tender beer to finished product to 0.5ug/L, but only a small amount of mercaptans in beer can produce a special yeasty and greenish flavor.

 Diacetyl taste 

The taste threshold of diacetyl was between 0.1-0.15mg/L, and the diacetyl content of dark and malt-flavored beers was slightly higher than that of light beers. Causes of Diacetyl Smell:

The high content of diacetyl is generally caused by technological reasons. One is the incomplete decomposition of α-acetolactic acid, and the other is the harmful bacteria such as football bacteria infected with beer, both of which will lead to high content of diacetyl, and the latter often fails to attract enough attention.

 Dimethyl sulfide (DMS) taste 

Dimethyl sulfide is volatile and is an important component of beer flavor substances. Experiments have shown that low concentrations of dimethyl sulfide are beneficial to the taste of beer, but high levels can produce an unpleasant coal-like or grilled corn taste. Taste thresholds vary widely, with a critical range of 150ppb and normal values below 100ppb. Dimethyl sulphide is not easy to taste in dark or strong beers. Causes of DMS smell:

The content of dimethyl sulfide in barley is not high, but its precursor substance DMSP is formed during the germination process, which is then decomposed into volatile DMS by heating and boiling in wort.The DMSP content in malt depends on the year and variety of barley harvested, the time, temperature and humidity of germination, the time, temperature and wort boiling intensity of scorch.The content of DMS and DMSP when wort is boiled is affected by mashing method, boiling temperature, boiling time, and pH value of wort (the higher the pH value, the stronger the boiling of wort, and the faster the decomposition of DMSP).

It should be noted that DMS is easily oxidized and combines with oxygen to form DMSO, which has a high boiling point and is not easily volatilized during boiling, and is reduced to DMS by yeast reductase during beer fermentation. Therefore, DMSO is the second precursor of DMS.

During the boiling process of wort, DMSP should be fully decomposed by heat. Evaporate the resulting DMS as completely as possible by boiling to evaporate. If the temperature and heating time can meet the process requirements, this effect can be achieved. However, in some breweries, although the newly installed wort boiling system is perfect, the boiling time cannot meet the specified requirements, causing the DMSP in the wort in the vortex sedimentation tank to decompose into DMS, and the DMS at this time can no longer be recovered from the wort. The wort evaporates. A high DMS content in the setting wort will definitely lead to a high DMS content in the finished beer. This is because in addition to free DMS, there is also DMSP in the wort.

 Taste defects caused by microbial contamination 

The taste defects caused by microorganisms, such as aging taste, will not be manifested in the finished beer immediately. After the microorganisms grow and multiply, their metabolites will harm the flavor of the beer. Through sensory tasting, this defect can be detected in time. Causes of microbial contamination:

They can multiply rapidly in the wort without yeast added, and some produce celery flavor, some produce polyphenol flavor, and it is dangerous to store the wort without yeast for a long time.The metabolites of aerobic bacteria are 2,3-butanediol, acetate and dimethyl sulfide.

The most dangerous beer harmful bacteria in beer production are Lactobacillus and Coccus. Lactobacillus cerevisiae can cause beer to have a sour taste accompanied by turbidity and precipitation. Lactobacilli cannot be completely removed by diatomaceous earth filtration or cardboard filtration, and some remain in sake. In addition to turbidity, cocci infection also produces diacetyl. Experiments show that every milliliter of beer contains 20,000 cocci, and the diacetyl value can reach 0.25 mg/L. In contrast to lactobacilli, cocci can be removed by diatomaceous earth filtration or cardboard filtration. Most of the cocci in the fermented beer below are secondary pollution during the filling process. After prolonged incubation, Gram-negative anaerobic bacteria can suddenly produce intense turbidity, which causes beer to produce a disgusting odor through its metabolites such as butyric acid, valeric acid, and acetic acid.