There is a magical flower hidden in your favorite beer

"Grind the malt into the wine vat, saccharify and boil to add hops. Yeast ferments magically, and the wine is filtered and bottled. The amber-gold liquid fills the wine glass, and the foam dances like clouds. The drinker is intoxicated and happy as the mellow and bitter tastes interweave." The poem describes beer. Whether it is a family dinner or a gathering with friends, open a bottle of beer, hold up a cup of amber liquid, take a sip, and the freshness of the malt and the soft foam make people feel comfortable. While drinking beer, I wonder if some questions emerge in your mind: Why does beer have a bitter taste? Why does beer have cloud-like foam? In fact, it is all related to a "magical flower" added to beer brewing - "I".

Figure 1 Photo of beer

My love affair with beer

Beer is made from malt, hops, yeast, water, etc., and is brewed through a series of process steps such as saccharification, boiling, and fermentation to produce a low-alcohol fermented wine with a unique flavor and rich foam[1]. In beer, malt is the "body", mainly providing sugar; yeast is the "heart", responsible for converting sugar into alcohol; water is the "blood", dissolving sugar and creating a suitable growth environment for yeast. It is no exaggeration to say that hops are the "soul" of beer, giving beer its unique flavor.

Figure 2 Beer brewing process [2]

Speaking of my love affair with beer, it has also been a long time. At first, I didn’t know beer. The Book of Documents, a book written in the Zhou Dynasty, states: “If you want to make wine and liquor, you should use koji and koji.” Koji refers to germinated grains; wine and liquor is wine made from koji and koji. The Sumerian clay tablet civilization recorded the unique “Sumerian way of drinking beer” - using a thin reed tube (the prototype of modern straws) to taste the fermented product of barley and water. Ninkasi is the “beer goddess” in the Sumerian pantheon. There is also a poem in the “Hymn to Ninkasi”: “Ninkasi, you are the one who pours the filtered beer from the urn, just like the rapids of the Tigris and Euphrates[3].” Whether it is the Zhou Dynasty’s “wine and liquor” or the malt juice made by the Sumerians, these beers fermented from sugar-rich malt do not have delicate foam, taste very sweet, and microorganisms are easy to reproduce in them, so the shelf life is short.

Figure 3: Sumerians tasting beer

Later, in order to balance the taste of beer and extend its shelf life, people played with beer in many ways. Beer made friends from all over the world, such as various fruits (such as cherries, grapefruits, dates, etc.), honey, various spices (such as heather, seaweed, spruce, wild rosemary, etc.), salt, and even cooked bread... But these are not beer's "dishes". It was not until 1079 that monks in a German monastery had a sudden idea to brew beer with a plant called hops[3]. As a result, we fell in love. Beer is like having a soul, with a sweet taste and a little bitterness. The aroma of wine and wheat complement each other to form a unique flavor, giving people a refreshing feeling. In addition, I also have the function of sterilization and disinfection, and the shelf life of beer is significantly increased. In the Middle Ages when plague was rampant, clean water sources were the guarantee of life, and beer became the "water of hope". Today, I also have a new name - hops!

Figure 4 Photo of hops

My "magical" magic

2.1 “I” am a bitter flower

I am a "bitter" flower. It is not that I have a strong bitter taste, but that I use magic to give beer a bitter yet refreshing taste. The bitter taste of beer mainly comes from the α-acids, β-acids and polyphenols in my body[4].

α-acid is composed of five homologues with different side chain R groups. α-acid itself has no obvious bitter taste, but the humulone, synhumulone, and synhumulone in it will undergo isomerization under light, heat, and alkali conditions [4][5]. Because it has chiral carbon atoms and has two structures, cis and trans, it can form six new substances after isomerization. To put it in an analogy, α-acid is a ball of plasticine that is kneaded into a palm-shaped plasticine under external conditions. The palms are divided into left and right hands. The palms of the two hands can overlap, but the palms and the backs of the hands cannot overlap, so they are two new substances. These new chemical substances are collectively called iso-α-acids, which have strong bitterness and solubility.

Figure 5 Structure of α-acids in hops[5]

Like α-acids, β-acids do not have a bitter taste that can be sensed by the taste buds. The reason why β-acids provide bitterness is that they are easily oxidized and will oxidize to form humulone during the wort boiling process. The bitterness intensity of humulone is 84% ​​of that of iso-α-acids, and its content in beer is about 1 to 2 mg/L[6]. The bitterness provided by phenolic substances is mainly related to the oxidation products and isomerization products of xanthohumol. However, compared with iso-α-acids, these substances only play a supplementary and modifying role. Iso-α-acids contribute about 80% to the bitterness of beer[6], and are the main force in producing the bitterness of beer.

The seven calabash brothers have different abilities, and the six isomers formed after the α-acid isomerize have different bitterness. Among them, cis-isohumulone has the strongest bitterness. The α-acid composition structure of different varieties of me is different, which results in different composition structures of iso-α-acid after isomerization, and the bitterness of beer is naturally different. The bitterness and thermal stability of cis-iso-α-acid are greater than those of trans-iso-α-acid, and the ratio of cis-trans isomers produced by α-acid under different conditions is different[4]. This is also the reason why different brands of beer have different bitterness due to different production conditions. In addition, the earlier I am added, the higher the utilization rate of bitter substances; the longer the boiling time, the more bitter substances dissolve[7]. So in my opinion, in order to brew beer that meets people's bitterness needs, the selection of varieties, the time of addition, the pH of wort, the metal ions in the wort, the intensity of wort boiling and the boiling time are all factors that need to be considered.

Table 1 The proportion of the six isomers of α-acids in the total α-acids in beer and their bitterness levels [4]

Table 2 Ratio of cis- to trans-isomers of α-acids under different isomerization conditions [4]

2.2 “I” am also a fragrant flower

When you use a bottle opener to open a bottle of beer, a whiff of aroma hits your nose, and this is also due to me. The aroma of beer mainly comes from the hop essential oils in my body, and is also related to yeast fermentation and malt aroma [5]. The aroma of beer is the result of the interaction of multiple components.

The aroma components of hop essential oil are very complex, and after complex reactions such as wort boiling and yeast metabolism, the aroma types are ever-changing. Fresh grass aroma can be attributed to aldehydes; citrus aroma can be attributed to esters, nerol and linalool; floral and fruity aromas are attributed to linalool, geraniol, β-ionone, 4MMP, 3-mercapto-1-hexanol and other ketones, epoxides and esters; herbal aroma can be attributed to oxidized sesquiterpenes [8]. Different varieties of hops have different composition components, and the brewed beer has different aromas. Scientists used beer brewed with six different varieties of hops as samples to create a sensory evaluation radar chart (Figure 6). The beer brewed by Qingdao Dahua is mainly woody and estery.

Figure 6 Sensory evaluation radar chart of beer brewed with six different hops [9]

When we cook rice porridge at home, the kitchen is always filled with the strong aroma of rice, but the aroma is not so strong when we drink the porridge. This is because most of the aroma components in the rice porridge have already escaped into the air during the cooking process. Similarly, there are some volatile substances in my aroma components, which are easy to escape into the air under high-temperature cooking, causing aroma loss. In the process of boiling beer, adding me later, reducing the boiling time and firepower can reduce the loss of volatile substances, thereby better preserving the aroma.

The problem is, if the boiling time is reduced, the bitter substances cannot be completely dissolved into the beer, and the taste of the beer will decrease. In order to make the bitterness of beer meet people's needs, the boiling time is generally about one hour. But such a long boiling time also loses a considerable part of the aroma components. This is really a matter of having your cake and eating it too! It's too difficult for me! In actual production, I am usually added multiple times at different stages of wort boiling to ensure the aroma and bitterness of the beer at the same time.

2.3 “I” am a romantic flower

I am a very romantic person. I know how to dress up and protect beer, making it charming among my drinking companions. Cloud-like foam, golden and transparent appearance and good antiseptic properties are all my gifts to beer.

Beer foam has the characteristics of foaming and stability. Foaming refers to the amount of foam produced, which is mainly related to the CO2 content. Beer is fermented by yeast. During the yeast fermentation process, CO2 is produced, which causes a certain pressure difference between the internal air pressure of the beer and the external atmospheric pressure. When the beer comes into contact with air, the supersaturated CO2 dissolved in the beer is released into the air due to the effect of atmospheric pressure. During the release process, bubbles are generated, gradually expand and gather together to form beer foam visible to the naked eye[10].

Figure 7 Photo of beer with cloud-like foam

The stability of beer foam refers to the length of time the foam exists in the air, which is mainly related to the surfactants in the beer. During the foam formation process, the chemical substances in the beer will be adsorbed on the surface of the bubbles as CO2 is released. Among them, the iso-α-acids produced by me can form a special surfactant with the foaming protein in the malt, which has a function similar to that of a surfactant. This substance can turn the hydrophobic iso-α-acids to the foam surface and the hydrophilic foaming protein to the inside of the foam, thereby improving the stability of the foam [3]. Of course, other ingredients in beer will also affect the stability of the foam, such as water, sugars, lipids, polyphenols, ethanol, metal ions, etc. [10].

Figure 8 Simple structure diagram of beer foam (self-drawn)

If you often buy beer and are used to checking labels, you will find that no preservatives are added to beer. This is because I have the function of antiseptic and antibacterial. It is recorded in "Food Chinese Medicine and Convenient Prescriptions": I have an inhibitory effect on many bacteria and have a sedative and estrogen-like effect. The α-acid in my body can act as a particle carrier on the cell membrane, reduce the proton driving force, hinder the transport of nutrients and thus cause cell death[11]. β-acid, hop essential oil, and polyphenols also have a certain inhibitory effect on beer spoilage bacteria. Among them, polyphenols can also combine with turbid proteins to form thermal coagulant precipitation when the wort is boiled[3]. After subsequent treatment, the body of the beer can be made purer and brighter, which is why beer has a gorgeous golden coat.

The ever -changing “ me ”

If you have read this far, you may have already checked the labels of your beer at home. But the words you see most often are "hop products". So are "hop products" and I the same thing? Hop products are products that I have processed, mainly "granular hops" and "hop extracts". Hop products are essentially me, but they are not presented in the form of plants.

Figure 9 Hop products (hop pellets on the left and hop extract on the right)

Here I want to support hop products. The rumor that beer brewed with hop products contains toxic chemicals is completely groundless! Granular hops are short sticks (similar to corn stick snacks) made by squeezing crushed hops and stored in inert gas. Hop extract is a concentrated paste made by efficiently extracting the effective ingredients in hops using supercritical carbon dioxide extraction technology. CO2 is non-toxic, colorless, odorless and tasteless, and is an inert gas. There is no chemical pollution in the conventional production process of hop products!

Do you know why most beer bottles are green or dark in color? This is mainly to reduce the phenomenon of "sunlight odor": the isomerized iso-α-acids in beer have poor light stability and will crack under light. The resulting fragments will react with sulfur-containing compounds to form 3-methyl-2-butenyl mercaptan[12]. This substance will emit a "skunk"-like odor. The reduced isomerized hop extract has good light stability and can effectively prevent the occurrence of "sunlight odor". Compared with ordinary hops, hop extracts also have the advantages of good solubility, high utilization rate, convenient transportation, and economical savings. The disadvantage of hop extracts is that they cannot completely extract the ingredients in hops that are useful for brewing, and the flavor of the brewed beer may be slightly worse.

Figure 10 Photolysis reaction of iso-α-acids[12]

Of course, whether it is beer brewed with me or hop products, it contains a certain amount of alcohol. The "Dietary Guidelines for Chinese Residents 2022" recommends that the daily alcohol intake of both men and women should be controlled within 15 grams. Taking beer with an alcohol content of 3 degrees as an example, 1500 mL divided by 3 to get 500 mL is the recommended daily intake of 3-degree beer. In addition, gout patients are advised not to drink beer. The alcohol and high content of purine in beer will increase the production of uric acid. When the uric acid produced exceeds the body's excretion capacity, uric acid will form uric acid crystals in the joints and trigger an inflammatory response. So, although beer is good, it should be consumed in moderation.

Conclusion

I am a small person, but I have a wealth of chemical knowledge. As people's understanding of me deepens, I have gradually entered the production fields of cosmetics, medicine, detergents and some baked foods [13]. my country attaches great importance to the research and development of new varieties of hops and the upgrading of brewing technology. Although there is still some gap between Chinese beer and world-renowned brands of beer, with everyone's efforts, one day the fragrance of Chinese hops will spread throughout the world!

References

【1】Han Beizhong. Knowledge of wine standards[J]. China Standards Guide, 2013(01):12-14.

【2】Wei Huayang, Wu Yashuai, Hou Yaxin, Chen Hao, Zhao Dongrui. Research progress on flavor and functionality of craft beer[J]. Food Research and Development, 2023, 44(16): 193-199.

【3】Su Genglin. The Millennium “Bitter Love” of Beer[J]. Encyclopedia Knowledge, 2013(14):22-23.

【4】Liu Yumei, Tang Jian, Liu Kuifang. Chemical research on hops and its relationship with beer brewing[J]. Brewing Technology, 2006(02):71-75.

【5】Zhao Juanjuan, Wang Yanfeng, Zhang Zhiqiang, et al. Research progress of beer flavor substances[J]. Journal of Food Safety and Quality, 2023, 14(08): 44-51.

【6】Liu Zechang, Liu Yumei. Beer bitterness and hop bitter substances[J]. China Brewing, 2019, 38(01): 13-19.

【7】Huang Rong. Factors affecting beer bitterness (source and detection)[J]. Beer Science, 2013(03):54-56.

【8】Schonberger C,Kostelecky T. 125th Anniversary Review:The Role of Hops in Brewing[J].Journal of the Institute of Brewing,2011,117(3):259-267.

【9】Xu Hengyuan, Ding Zhicheng, Wang Xiaochen, et al. Research on aroma components and brewing characteristics of domestic hops[J]. China Brewing, 2022, 41(10): 49-54.

【10】Cao Rongkun. Effects of beer adjuvants on beer foam[D]. Jiangnan University, 2018.

【11】Wang Xiaochen, Mou Hong, Sun Shaokang, et al. Tolerance of beer-related microorganisms to isomerized hop extracts[J]. Brewing, 2022, 49(05): 73-77.

【12】Lin Liuyue, Jiang Yiping, Zhang Qiaoyan, et al. Research progress on chemical components and pharmacological activities of hops[J]. China Journal of Traditional Chinese Medicine, 2017, 42(10): 1830-1836.

【13】Dong Yanhu. Research on extraction and application of hop extract[J]. Agricultural Science and Technology Information, 2017(18):43-44.

Source

Figures 1, 4 and 7 are from www.unsplash.com

Figure 3 and Figure 9 are from the website https://www.sohu.com/a/438533253_100019214

Figure 2Figure 5Figure 6Figure 10Table 1Table 2 from the literatureFigure 8 self-drawn