The main factors that cause beer odor are: raw materials, processes, harmful substance pollution, microbial pollution, transportation and sales conditions.
The causes of common taste defects in beer and their preventive measures are as follows:
(1) Uncomfortable bitterness
Consumers often accuse beer of having an uncomfortable bitter taste, which is mostly manifested as an insimistic entrance
The reasons are mainly raw materials and process.
(1) Raw materials
a. The residual alkalinity, total hardness, magnesium ions, iron ions, and manganese ions in water are too high.
b. The quality of hops is poor, and the hops have aged after a long period of storage, and the place of origin is not ideal.
c. Poor malt quality, such as rough wheat hurd and high protein and tanning, roasting temperature is too high (caramelized malt or colored malt).
(2) Process
a． Brewing process. The saccharification and wort filtration time is long, so that excess tannins, anthocyanins and fatty acids enter the wort, and the filtered wort is cloudy. Too much oxygen is fed into the wort when unloading, stirring and pouring. Polyphenols react with oxygen; the last wash of water is used when saccharification.
b． Fermentation and post-storage processes. The separation effect of hot and cold coagulated matter is not good; the bubble cap is sunken and dissolved in the wine; the process pipe grows moldy; the storage temperature is too high, and more yeast enters the storage tank; the content of high alcohols and esters produced by fermentation is too high.
(3) Preventive measures
a． Strict control of raw materials, unqualified quality malt and aged hops can not be used.
b． Water quality can not meet the requirements must be water treatment, to regularly carry out physical and chemical analysis and sensory inspection of water quality.
c． To improve the boiling effect, the amount of hops added should not be too low, the diameter of the whirlpool groove should be reasonable, and the flow rate of wort inlet should be controlled.
d. Improve the separation effect of condensate. Cold wort filtration and flotation separation methods are generally used. When using the flotation method, we should pay attention to wort ventilation, the amount of ventilation is not less than 300-400/t wort, and the air distribution should be uniform, so that the separation of the fruit can reach 50% to 60%.
(2) Yeast taste
Yeast flavor is an uncomfortable smell and taste, especially when yeast is self-dissolving. Beers with a yeast flavor tend to have a high pH, dark color and poor foam performance.
(1) What causes yeast taste
a. The storage temperature is high and the storage time is too long, and the yeast dissolves and releases fatty acids. Studies have shown that these substances can make beer have an uncomfortable odor and adversely affect foam, in which ethyl acetate and ethyl dodecanoate can work together to form a yeast flavor when the content is high, but one of them does not work alone.
b. Hygiene problems such as mold growing in pipes. It can also lead to yeast confusion in beer.
(2) Preventive measures
a. The yeast should be discharged multiple times during the post-fermentation period of the conical tank. Prevents yeast from self-dissolving.
b. Test the yeast so that it remains in good physiological condition, and the use of algebra can not be too high.
c. Pay attention to detecting the content of caprate in beer. The content of caprate is significantly elevated when yeast is autolyzed, so it is an indicator of yeast flavor. Its content can be analyzed to determine whether the beer has a yeast taste.
(3) Fruit flavor (flavor characteristics of craft beer)
(1) The fruit flavor in beer is mainly formed by esters, and different esters have different taste thresholds (see table below)
(2) Preventive measures
a. Select yeast species with appropriate ester production levels. b. The use of low-temperature fermentation process, appropriate increase in the amount of yeast added, early ventilation, shorten the storage time, will strongly inhibit the formation of ester ester.
c. The concentration of wort should not be too high, the higher the concentration of wort, the higher the content of esters.
d. The height of the fermentation tank should not be too high, and the higher hydrostatic pressure and co2 content cause an increase in the ester content. Therefore, the ester content of beer produced by pressurized fermentation is high.
(4) The raw green taste of beer
The rawness of beer is generally described as immature in smell and taste. It is generally composed of diacetyl, acetaldehyde and sulfur-containing compounds.
(5) Phenol obscurity
People often describe the smell of phenol as a disinfectant smell, a smoky taste and a musty taste. The taste threshold of phenol is 30 ug/L, and the malt should contain 50 ug/100 g of dry matter.
(1) Causes of phenol flavor
a. The water contains phenol and enters the beer.
b. The brewing water is treated with ion exchange resin, and the acid used for resin regeneration is impure, and the result is that the brewing water is contaminated
c. Improper selection of cleaning agent or incomplete rinsing after using cleaning agent.
d. Storage of diatoms in a humid environment and the use of moldy packaging paper bags will cause beer to produce a musty taste similar to phenol.
e. Microbial contamination is also an important cause, Eich's E. coli, Klebsiella and wild yeast can produce 4-vinyl guaifosylol and 4-ethylbenzoic acid, resulting in a phenol flavor of beer.
f. Malt over-baking can also bring smoke to beer.
a． Regular analysis and tasting of the water quality of the brewery's water source is carried out to prevent phenol contamination of the water source.
B. The chemical agents used in the production process should be carefully analyzed and quality checked to prevent chemical pollution
c. Correctly select the cleaning agent and cleaning process, and eliminate the residue of the cleaning agent.
d. Test the quality of diatomaceous earth to prevent mold and absorption of heterotopia.
e. Strict hygiene management to prevent microbial contamination.
F. In the processing of raw materials, it is necessary to prevent over-baking and avoid the smoky taste of beer.
(6) Taste defects caused by microbial contamination
Taste defects caused by microbial contamination, such as, will not be immediately manifested in the finished beer, and after the microorganisms have grown and multiplied, their metabolites will be harmful to the flavor of the beer. Through sensory tasting, this defect can be found in time. They can multiply rapidly in the molded wort of the end yeast, some produce celery flavor, some produce polyphenol flavor, and the wort without yeast is dangerous to store for a long time.
(1) The metabolites of aerobic bacteria in beer are 2,3-butanediol, acetate, and dimethyl sulfur. The oxygen dissolved in wort is quickly consumed by yeast, so aerobic bacteria are not easy to multiply and are not a threat to beer.
The most dangerous anaerobic bacteria for beer are lactobacillus and cocci. Lactobacilli can cause beer to have a sour taste accompanied by turbidity and precipitation. Lactobacillus cannot be completely removed in diatomaceous earth filtration or cardboard filtration, and still partially remains in sake. In addition to turbidity, coccidioid infection also produces double acetyl, and experiments have shown that each milliliter of beer contains 20,000 cocci, and the double acetyl value can reach 0.25mg/L. In contrast to Lactobacillus, Cocci can be removed in diatomaceous earth filtration or paper wrench filtration. Most of the cocci that appear in the fermented beer below are secondary contamination during the canning process.
After a long incubation period of time, Gram-negative bacteria suddenly produce a strong turbidity, which produces a disgusting odor of beer through its metabolites such as butyric acid, valeric acid and acetic acid.
a. Strengthen hygiene management to ensure the hygiene of beer production.
B. Strictly clean and disinfect equipment and pipelines, often check the concentration, temperature and use time of the cleaning agent, and strengthen the management of the dead end of process hygiene.
c. Establish a sound sanitary sampling point, carry out strict hygiene testing of the whole process of production, semi-finished products and finished products, and conduct the inspection of anaerobic microorganisms when conditions permit.
d. The sensory tasting of beer should be institutionalized in order to find problems in time and take effective process measures.