How to avoid bad flavor in beer

Beer is malt as the main raw material, with hops added, fermented by yeast, and it is a kind of beverage containing carbon dioxide and low alcohol content. As a popular food, its flavor, foam, color and other indicators are important factors that affect consumers, and the influence of flavor is the most prominent.

Higher alcohols, aldehydes, diacetyls, organic acids, lipids and sulfur compounds in beer have an important effect on the flavor of beer.These by-products together with alcohol and carbon dioxide form the body of beer and form beer Unique flavor, these substances exist at the same time, and exert a combined influence on the flavor of beer. When one or more of its substances are too high, it will change the flavor characteristics of beer and form beer flavor defects, especially fermentation by-products. Their content is very small, but even small fluctuations will bring great flavor to beer flavor. Impact

The flavor defects of beer mainly include rough taste, unhealthy bitter taste, long after-bitter taste, phenol or other chemical taste, aging taste, rancid rice taste, rotten grass taste, onion taste, yeast taste, metal taste, musty taste, wheat hull taste , Thick taste and so on. These will have a huge impact on beer taste and reduce the quality of beer. The reasons and solutions are described below.

1. Harsh taste

Cause:

⑴ Too high content of polyphenols and too high degree of polymerization of polyphenols are the main sources of astringency in beer.

⑵Beer oxidation, beer pH is too high.

(3) The malt bark is thick and crushed too fine.

⑷The hardness of water is too high and the pH is high.

⑸ Hops are old, with long storage time and high storage temperature.

⑹Long boiling time, polymer polyphenols are easily oxidized.

⑺Excessive washing, the pH of the washing water is high, resulting in a large amount of polyphenols in the wheat skin

Solution:

⑴ Avoid excessive washing, the pH of washing water is controlled between 6.0～6.5.

⑵ Use fresh hops, hops should be stored in a low temperature (not higher than 4 ℃), dry environment, oxidized hops can not be used.

(3) Under the premise of not affecting the wort filtration, increase the degree of malt crush.

⑷Under the premise of guaranteeing the boiling intensity between 10% and 14%, the boiling time should be controlled at about 80min.

⑸ To avoid the inhalation of oxygen during the saccharification process, the bottom of the sugar and gelatinization pot can be used, and the boiling pot is closed to reduce the number and speed of saccharification. CO2 or N2 is used as a protective gas to replace the air in the pot.

⑹After removing most of the temporary hardness by adding gypsum to the brewing water, adding acid reduces the alkalinity of the water and lowers the pH.

2. Bitter taste is not correct, the bitter taste is long

Cause 

(1) The hops are outdated, the β-acid oxidation is serious, and the hops addition is too high.

⑵ The content of polyphenols is too high and the degree of polymerization of polyphenols is too high.

(3) The pH of saccharification water is too high and the alkalinity is large.

⑷ Overheated wheat grains.

⑸Wort boiling strength is not enough, and the content of solidified nitrogen is high.

⑹Wort boiling strength is too long, leading to the oxidative decomposition of iso α-acid.

⑺ The separation of wort coagulum is not good.

⑻ Fermentation is not vigorous, and the bitter blister cap is not completely separated or cannot be separated at all (such as pressurized fermentation, conical tank fermentation, etc.).

⑼ Yeast bitterness, excessive heavy metal content, beer oxidation, etc.

Solution 

⑴Adjust the amount of hops properly and adjust according to the content of α-acid in hops.

⑵Add acid to brewing water to reduce alkalinity and lower pH.

(3) Avoid excessive washing, and control residual sugar between 1.0% and 1.5%.

⑷ Increase the boiling intensity between 10% and 14%, and control the boiling time to about 80min.

⑸ Lowering the wort pH between 5.2 and 5.4 is conducive to the precipitation and separation of coagulum, and the bitter taste is fine and pure.

⑹In the early stage of fermentation, open fermentation is carried out to make the fermentation vigorous.

⑺Wort wort oxygenation is moderate, do not over-oxygenate.

3. Phenol or other chemical smell

Cause :

⑴The paint contains phenol or chlorophenol.

⑵ Use phenol, chlorophenol and high free chlorine to soak wheat and saccharify.

(3) Scrub the wine delivery pipeline with a detergent containing free chlorine.

⑷ Contamination of wild yeast or bacteria.

Solution :

⑴ The inner wall of the fermentation tank is made of non-odorous paint and stainless steel pipeline.

⑵ Use phenol, chlorophenol and low free chlorine to soak wheat and mash.

(3) Brush the wine conveying pipeline with detergents and fungicides that do not contain free chlorine.

⑷Strengthen the process hygiene management to prevent the pollution of harmful bacteria.

4. Aging smell

Cause

⑴ Oxygen can lead to the rapid decline of beer and cause some very important aging reactions.

⑵The generated carbonyl compound causes aging aldehyde condensation reaction

⑷ Maillard reaction

⑸ Synthesis and hydrolysis of volatile fat

⑹Synthesis of dimethyl sulfide

⑺ Degradation of polyphenols.

Solution:

⑴ It is best to use CO2 or N2 to protect the raw and auxiliary materials during crushing. It is not easy to take too long after crushing and before feeding.

⑵The equipment is protected by CO2 or N2 during the mashing process, and the bottom feed is used when pouring the mash.

(3) During the saccharification process, reduce the number of mash stirring as much as possible and reduce the stirring speed.

⑷ Pumps, seals, valves, etc. must not leak, strengthen maintenance. ⑸The door should be closed when the wort is boiled. The boiling time should not be too long.

⑹After the main fermentation, the wine should be released as soon as possible. The post-fermentation tank used for CO2 preparation uses pressure to control the speed of the liquor entering the post-fermentation tank less than 1m/s.

⑺Before drinking, the empty pipeline is used to lead the wine with deoxygenated water. At the end of the wine, CO2 is used to top the wine.

⑻When the high-concentration dilution method is used to filter wine, the purity of the CO2 gas used to prepare deoxygenated water is above 99.998%.

⑼When filtering wine, use sterile water to clean the air in the filter, and then use deoxygenated water to clean the sterile water in the filter.

(10) During the wine filtering process, the diatomaceous earth and various additives cans are protected with CO2 or N2.

⑾Wine head and tail are stored separately, and then washed with CO2 before use.

⑿Before pouring wine, the wine receiving pipe will be enriched with deoxidized water to lead the wine, and the wine tank will be prepared by CO2.

⒀The wine filling machine adopts secondary vacuum, and the vacuum degree reaches -0.080Mpa or more.

⒁Filling machine filling at a uniform speed to keep the pressure of the wine tank stable and avoid frequent stop driving.

⒂Check the wine valve frequently, and replace it in a timely manner if it is damaged to prevent vortexing and oxygen absorption.

⒃Before capping, use a high-pressure foaming device to foam, reduce the bottleneck air content to less than 1mL (1mL bottleneck air can increase the dissolved oxygen in the bottle of wine by more than 400μg/kg). Control the pressure of the foam above 1.0Mpa, and the temperature above 85℃. During the foaming process, the stream of foam should be aligned with the bottle mouth and hit the surface of the bottle of clean liquor to make the wine evenly foam and exclude the bottleneck air. The foam must be delicate. Flee to the mouth of the bottle and immediately press the cap.

⒄Control PU value between 9～15.

5. Rancid rice flavor

Cause: 

The content of diacetyl in beer exceeds its taste threshold, which will give the beer an unpleasant rancid taste. The flavor threshold is also relatively low. For the light-type light-colored lager beer, the diacetyl content should be controlled below 0.1mg/L; for high-end beer, it is best to control it below 0.05mg/L.

Solution

⑴ Properly increase the content of α-amino nitrogen in wort, generally for 12°P wort, the content should be controlled at 180±20mg/L. Too low will result in the synthesis and accumulation of α-acetolactate; too high will result in yeast overnutrition and higher alcohol content.

⑵Reduce the multiplication factor of yeast, generally the multiplication factor is ≤3. Because the precursors of diacetyl and other yeast metabolic by-products are mostly produced in the process of yeast reproduction, we can take a series of measures such as low temperature inoculation, increased inoculation volume, and low temperature fermentation to reduce the yeast proliferation rate.

⑶ Properly increase the fermentation temperature in the late stage of the main fermentation.

⑷ Maintain a certain concentration of yeast cells in the late stage of fermentation.

⑸Reduce the dissolution of oxygen in the process of filtering wine. During the process, take measures such as CO2 or N2 protection, and no bubbles in the pipeline.

⑹Reduce the dissolution of oxygen during filling. During the process, measures such as secondary vacuum pumping and high-pressure water foaming were taken.

⑺ Breeding yeast strains with low peak value of α-acetolactate, that is, strains with low activity of α-acetylhydroxybutyrate synthase to reduce the accumulation of diacetyl precursors.

⑻Adding appropriate amount of α-acetolactate decarboxylase to the cold wort just beginning to ferment, can directly decarboxylate α-acetolactate to acetoin without passing through diacetyl.

⑼Strictly pay attention to process hygiene management to avoid yeast being contaminated with cocci and lactic acid bacteria and other bacteria, resulting in a large amount of diacetyl in beer.