About those flavor substances in beer

Brewing a high-quality beer is not so easy, because there are always some unavoidable interference factors in the brewing process, which will make the beer have one or another flavor defect. Therefore, understanding the various flavor defects of beer and their causes will help us to effectively control them during brewing, thereby avoiding or reducing their occurrence.

Diacetyl

Diacetyl is an important indicator of beer maturity. In the process of brewing pale beer, it is recommended that the content of diacetyl be controlled below 0.05mg/L. If the content exceeds 0.1mg/L, it will seriously affect the quality and taste of beer and produce an unpleasant smell of rancid rice.

Causes: There are raw material reasons, and there are more process factors; the content of pyruvate is too high; the content of α-acetolactate in the fermentation liquid is too high; the yeast proliferation is inconsistent and irregular in the early stage: the yeast activity is poor and the reducing power is low; the post-fermentation process , The temperature setting is unreasonable; bacteria are contaminated during the fermentation process, etc.

Dimethylsulfide (DMS)

DMS is one of the most noticeable and highly volatile sulfur-containing organic compounds in beer, and the concentration range of different beers is also different; it generally has the smell of boiled corn or cooked onion, and its flavor threshold is relatively low. Low, tends to exceed its flavor threshold in some beers.

Cause:

1. Raw materials: Malt is the main source of DMS in beer. In addition to DMS, malt also contains precursors of DMS, S-methylmethionine (SMM) and dimethyl sulfoxide (DMSO); DMS in finished beer mainly comes from Degradation of its precursor SMM; DMSO was reduced to DMS by yeast during fermentation; and a small amount of DMS may come from hops.

2. Saccharification: When boiling, if SMM is not completely decomposed into DMS or evaporates completely, it is part of the source of boiling, so the intensity of boiling, boiling intensity, and time often determine the content of DMS.

3. Fermentation: temperature affects the content of DMS; some wild yeast or bacteria can also produce DMS.

4. Equipment: The unreasonable design of some sedimentation tanks will also cause the rise of DMS. Therefore, it is necessary to shorten the residence time of hot wort and appropriately increase the cooling rate of wort.

Ethyl acetate

Ethyl acetate is the most important ester with the highest content in beer. The sum of it and isoamyl acetate accounts for more than 80% of the total ester in beer. The threshold value of ethyl acetate is about 30mg/L, and the content in beer is generally 14~25mg/L. It can give beer a strong stimulation, fruity aroma, and solvent smell.

Cause: As one of the important esters in beer, it has an important influence on the flavor of beer. The synthesis of ethyl acetate is closely related to the selection of strains. It mainly comes from the metabolism of yeast; in addition, process settings, equipment The situation is also one of the reasons that cannot be ignored.

Acetaldehyde

Acetaldehyde is the aldehyde with the highest content in beer, and its content directly affects the quality of beer. A high content of acetaldehyde will bring unpleasant "grassy, depressed, raw green" to beer and the feeling of immature wine. In addition, drinking beer with high acetaldehyde content will cause uncomfortable physiological reactions such as "upper head and headache".

Causes: Acetaldehyde in beer is mainly metabolized by yeast, which is an intermediate product of sugar metabolism; the amount of oxygenation in the early stage of the main fermentation is too high and the amount of yeast inoculum is too large, which often produces a high amount of acetaldehyde; yeast aging, Poor activity and incomplete fermentation can also easily increase the acetaldehyde content in beer; of course, there are some other factors that can also cause aldehydes to increase and affect the quality of beer.

Isoamyl alcohol

Higher alcohol is one of the main substances that form the flavor of beer. When its content is too high, it will also cause the feeling of "head, headache, dizziness". Higher alcohols are mainly isoamyl alcohol, which brings the smell of fusel alcohol and bitter almond to beer, and its threshold value is about 55mg/L; followed by active amyl alcohol, n-propanol, isobutanol, etc. It is produced during high-temperature fermentation and the early stage of fermentation.

Causes: The selection of strains, high oxygen content in wort, small yeast inoculum, large multiplier, high fermentation temperature, fermentation without pressure in the main fermentation, etc., can all lead to an increase in the content of higher alcohols; in addition, wort α -Excessive (or inappropriate) amino acid content will also cause decarboxylation or deamination of amino acids to generate higher alcohols.

Trans-2-nonenal

Trans-2-nonenal, which tastes offensively cardboard, is representative of oxidative notes, a flavor defect caused by beer oxidation. In oxidized beer, the threshold value of trans-2-nonenal is extremely low, about 0.0001mg/L.

Causes: melanoidin and polyphenols in an oxidized state produce typical aging substances from the oxidation of higher alcohols; during the storage of finished beer, dissolved oxygen in the wine is catalyzed; some carbonyl compounds in the wort are not fermented Being fully restored and so on are all incentives.