Study on Brewing Characteristics of High αacid and High βacid Hops

Yanwei GUO Cong NIE Xueqin GUAN Jie ZHANG Guiheng YANG

Abstract [Objectives]Columbus and Tsingtao Flower were selected to brew Ale beer， thereby studying the brewing characteristics of high acid and highacid content hops.[Methods]The content of diacetyl and bitterness in beer were determined by a spectrophotometer at 335 and 275 nm， respectively. With pH=8.2 as the end point of potentiometric titration， the total acid content in beer was calculated by acidbase titration method， and sensory evaluation for beer was conducted.[Results]The results show that acid is an important factor affecting the production and reduction rate of diacetyl in beer. The production and reduction rate of diacetyl in high acid hops were lower than those in highacid hops; isoacid was the main source of bitterness in beer， and high acid hops had more significant bitter value than highacid hops; and malt acid compounds and fermentation production were the main source of total acid in beer， and high acid and highacid hops had a little effect on total acid in beer. In sensory evaluation， high acid hops were more effective than highacid hops in terms of zest of the mouthfeel， foaming retention and alcohol fragrance， while in clarity， high acid hops were lower than highacid hops.[Conclusions]Therefore， we can draw a conclusion that the brewing characteristics of high acid hops are better than those of highacid hops.

Key words Hops; High acid; Highacid; Diacetyl

Hops give the beer its unique bitterness and aroma， and are known as the "soul of beer"[1-2]. The main components of hopshop resin， hop oil， and polyphenols play an important role in the brewing process[3-4]. The hop resin can be classified into a soft resin and a hard resin， and the soft resin is mainly composed of an acid and aacid[5]. Alphaacid is the main source of bitterness in beer， and it is easily soluble in organic solvents such as ether and methanol[6-7]. It has strong bitterness and strong anticorrosion ability， and can increase the stability of beer foam. Theacid is hardly soluble in water， and its bitterness， antiseptic ability and acidity are weaker than acid; and it is more easily oxidized into a soft resin having a large bitter taste. The hop oil is not easily soluble in water and is the main source of hop aroma[8]. Polyphenols have oxidizing and reducing properties and are the main components that affect beer flavor and cause beer turbidity[9-10].

Recently， craft beer has developed rapidly. Craft beer pays more attention to the bitterness and aroma of beer[11-12]. This work used high alphaacid content of Columbus hops and highacid content of Tsingtao Flower. The area of Columbus hop is one of the largest in the United States， with acid content as high as 14% to 16%. It has a pure bitter taste and is a kind of bitter flower that can be used to make heavycolored beer such as pastel Aier， IPA， Shitao. Tsingtao Flower， which is the main cultivar in China， is favored by major domestic beer manufacturers. Itsacid content reaches 3% to 5%， with a soft aroma and a balanced bitterness[13]. The brewing characteristics of high acid hops and highacid hops were determined by testing the total acidity， bitterness value， diacetyl content and other physical and chemical indicators of beer and testing of sensory evaluation[14-15].

Materials and Methods

Beer brewing

The traditional method of adding hops when boiling was chosen， and the same amount of different varieties hops， the Columbus hop with acid content of 14% to 16%， and the Qingdao big flower withacid content of 3% to 5%， were added to carry out the experiment under the optimal brewing conditions. The experiment was carried out under the same condition， and brewing procedures are as follows：

（1） Malt crushing： The mill was pulverized with a pulverizer to break the bark of the barley and the contents were in a fine state.

（2） Saccharification： The saccharification process of singletemperature leaching saccharification method was chosen. The feed water ratio was 1≥4; and the temperature was kept at 55 for 30 min and then raised to 65， which was kept for 60 min and then raised to the temperature of 72， which was kept for 10 min and then raised to 78 to terminate the saccharification.

（3） Filtration： The mash was added to the filter tank and allowed to stand for 20 min. The wort was refluxed firstly， and filtered when the wort was clarified. The washing was started when the wheat grains were about to be exposed to the liquid surface， and the temperature of the washing water was 78. After the washing， the filtration was stopped.

（4） Boiling： The obtained wort was equally divided into two portions and boiled. After 30 min， Columbus hops and Qingdao big flowers were added to the two boiling pots， respectively. The amount of hops added was 1 g/L， and the boiling was continued for 60 min. Finally， the raw wort concentration was 12.0 °P.

（5） Cooling： The boiled wort was cooled to about 18 to 20.

（6） Inoculation： 10 g of dry yeast was added to 200 ml of sterile water for activation. Then， the yeast liquid was inoculated to the wort， separately.

（7） Fermentation： The temperature of fermentation was 18 to 20. The can was sealed when the sugar level dropped to 4 °P.

Determination of diacetyl content in beer

The content of diacetyl was determined when the sugar content of beer dropped to 4 °P. The diacetyl can react with ophenylenediamine after distillation cooling. The reaction is as follows： diacetyl + ophenylenediamine∪2，3dimethylquinoxaline. The hydrochloride of the product had an absorption peak at 335 nm wavelength， and the content of diacetyl in beer was calculated by measuring its absorbance[16].

Calculating method： X=A335*1.2

In the formula： X is the diacetyl content of the sample， mg/L; A335 is the absorbance of the sample at 335 nm wavelength; and 1.2 is the conversion coefficient of absorbance and diacetyl content.

Determination of bitterness of beer

A pipette dipped with a trace octanol was used to absorb 10 ml of the beer sample to a 50 ml centrifugal tube， into which 1 ml of 3 mol/L hydrochloric acid and 20 ml of isooctane were added. The centrifugal tube was cover with a plug tightly and vibrated on the oscillator for 15 min. The supernatant was transferred into the spectrophotometer colorimeter dish as soon as possible. Isooctaneoctanol （adding 1 drop of octanol to 20 ml of isooctane） was used as blank at 275 nm to determine the absorbance of the sample at 275 nm[17-18].

Calculating method： Bitterness value （BU）=A275 nm*50

Wherein： A275 nm is the absorbance of the sample， and 50 is the conversion coefficient.

Determination of total acids in beer

According to the principle of acidbase neutralization， the total acid in beer was directly titrated with sodium hydroxide standard solution. The end point of potentiometric titration was pH=8.2. The total acid content in beer was calculated according to the volume of sodium hydroxide standard solution consume. The standard buffer solution was used to correct the instrument， and the liquid beads attached to the electrode were absorbed by filter paper to keep the electrode dry after the instrument was cleaned by distilled water. Then， 50.00 ml of sample was absorbed by pipette and placed in a beaker and the power supply was connected. The electrode was inserted， and the electromagnetic stirrer was opened and titrated while stirring. When the standard solution of sodium hydroxide was titrated to pH=8.2， the titration was stopped and the volume of the standard solution consumed by sodium hydroxide was recorded.

Calculating method： X = 2 *c *V

Wherein X is the total acid of sample; c is the concentration of sodium hydroxide standard solution， mol/L; V is the volume of sodium hydroxide standard solution consumed， ml; and 2 is the coefficient converted to 100 ml of sample.

Sensory Evaluation

Two groups of tasters were invited to evaluate the beer samples. The sensory characteristics of beer， such as zest of the mouthfeel， dizziness， mellow fragrance， soaking holding capacity， clarity and bitterness， were evaluated with a score of 0-10. The samples were divided into five groups， and the flavor radar map was made by blind evaluation according to the average score.

Results and Analysis

The effects of high acid hops and highacid hops on the reduction rate of beer diacetyl

When the beer sugar content was reduced to 4 °P， the diacetyl content of the wine samples containing Columbus hops and Tsingtao Flower was determined. The results are shown in Fig. 1.

Diacetyl is an important factor affecting the flavor of beer. If it is slightly controlled during the beer production process， the flavor of beer will change and the taste of beer will lose its refreshing taste. The national standard premium grade beer requires a diacetyl content less than 0.13 mg/L. It can be seen from Fig. 1 that for the high acid hops， i.e.， the Columbus hops， the amount of diacetyl was low， and the reduction rate was also slow， while for the highacid hops， i.e.， the Tsingtao Flower， the amount of produced diacetyl was high， and the reduction rate was also fast.

The effects of high acid and highacid hops on total acid and bitterness of beer

The beer made in Columbus hops and Tsingtao Flower was chosen. The total acid content and bitterness value were tested separately， and the results are shown in Fig. 2.

The total acid in beer was generally between 1.7 and 2.3 mg/L. Fig. 2 shows that high acid hops and highacid hops had a slight effect on total beer acid， but it was not the main influencing factor; and the beer taste of high acid was much higher than that of highacid hops.

Sensory evaluation

The beer made in Columbus hops and Tsingtao Flower was chosen， and two groups of wine tasters were invited to evaluate beer samples. The results of the evaluation are shown in Fig. 3.

Yanwei GUO et al. Study on Brewing Characteristics of High acid and Highacid Hops

According to the taster， the high acid hops were zest of the mouthfeel， soaking， and mellow were higher than the highacid hops， and were almost same in the dizziness， and in the clarity， the high acid was not as good as highacid hops.

Discussion

The effects of high acid and highacid hops on the reduction rate of beer diacetyl

The acid in hops is converted into isoacid during the boiling process of wort. Generally， the acid isomer ratio can reach 40% to 60%. Isoacid is one of the important factors affecting the activity of yeast. Columbus hops had high acid content， so its high acid content led to low yeast activity， which hindered the process of acetolide to diacetyl. The amount of diacetyl formation was low， and the activity of diacetyl reductase was lowered， resulting in a decrease in the rate of reduction of diacetyl. On the contrary， Tsingtao Flower had low acid content， so its low acid led to its relatively high yeast activity， which made the process of acetolidine diacetyl formation less hindered， and its diacetyl production was relatively higher， the activity of diacetyl reductase was so strong that the rate of diacetyl reduction was faster than that of Columbus hops.

The effects of of high acid and highacid hops on total acid and bitterness of beer

The acid content of Columbus hops was as high as 16%-18%， while the acid content of Tsingtao Flower was 5.5%-7.0%， and theacid content was 3.0%-5.0%. The acid content of Columbus hops was higher than that of Tsingtao Flower hops. This might be one of the reasons for the final detection of high alphaacid hops total acid content higher than high betaacid hops. The malt acid and fermented acid are the main sources of total beer， so the wort and acid production during fermentation might have a greater impact on total acid. The bitterness in beer mainly comes from isoacids， and the isoacids mainly include three structurally similar homologues such as isohumulone， isohumulone， and isohumulone. During beer brewing， the acid in hops isomerizes to isoacid during the boiling process of wort. Usually， the isomer ratio can reach 40%-60%. The solubility of isoalpha acid in wort is much higher than the acid. The solubility of isoalpha acid in wort is the main source of bitterness in beer. Compared to acid，acid is extremely unstable and degrades rapidly during the boiling of wort.

Sensory evaluation

According to the taster， the beer brewed by Columbus hops was superior to the beer brewed by Tsingtao Flower in terms of zest of the mouthfeel， dizziness， mellowness， soaking and bitterness. The beer brewed by Tsingtao Flower was superior to the beer brewed by Columbus hops in terms of clarity. Overall， the brewing characteristics of Columbus hops were superior to the brewing characteristics of Tsingtao Flower. The research of hops is important for improve the quality of beer， therefore， this work chose water， barley malt， Columbus hops and Tsingtao Flower， yeast， and used the above fermentation to make beer， in order to explore the effects of high alpha acid and high beta acid hops to the beer brewing. However， there are still many improvements that can be improved in this study due to factors such as experimental conditions and time. Further researches about the brewing characteristics of hops such as the aroma， stability， and hop aging of high acid and highacid hops should be obtained.

References

[1]WIETSTOCK PC， SHELLHAMMER TH. Chelating properties and hydroxyl scavenging activities of hop acids and isoacids[J]. J. Am. Soc. Brew. Chem.， 2011， 69： 133-138.

[2]TING P， HOPPE M， NAVARRO A， et al. Method of hydrogenating isoacids in a buffered solution[P]. U.S. patent 6， 303， 824， 2001.

[3]TING PL， KAY S， RYDER D. Separation and identification of stereoisomers of isomerized acid derivatives by HPLC/DAD and electrospray HPLC/MS[J]. J. Am. Soc. Brew. Chem.， 2007， 65： 9-14.

[4]TING P， GOLDSTEIN H. Concentrated single phase aqueous solutions of tetrahydroisoacids and methods of preparing the same[P]. U.S. patent 5， 874， 633， 1999.

[5]TECHAKRIENGKRAI I， PATERSON A， TAIDI B， et al. Relationships of sensory bitterness in lager beers to isoacid contents[J]. J. Inst. Brew.， 2004， 110： 51-56.

[6]KUNIMUNE T， SHELLHAMMER TH. Foamstabilizing effects and cling formation patterns of isoacids and reduced isoacids in lager beer[J]. J. Agric. Food Chem.， 2008， 56： 8629-8634.

[7]EVANS DE， SURREL A. Comparison of foam quality and the influence of hop acids and proteins using five foam analysis methods[J]. J. Am. Soc. Brew. Chem.， 2008， 66： 1-10.

[8]FRITSCH A， SHELLHAMMER TH. Relative bitterness of reduced and nonreduced isoacids in lager beer[J]. J. Am. Soc. Brew. Chem.， 2008， 66： 88-93.

[9]BOLØVAR A， GASPARRI M， ZUFALL C. A rapid and lowcost method for quantification of reduced isoacids in brewing[J]. J. Am. Soc. Brew. Chem.， 2006， 64： 39-46.

[10]COWLES JM， GOLDSTEIN H， CHICOYE E， et al. Process for separation ofacids from extract containing acids andacids[P]. U.S. patent 4， 590， 296， 1986.

[11]KROFTA K， VRABCOVA S， MIKYS?KA A， et al. Stability of hop beta acids and their decomposition products during natural ageing[C]//Proceedings of the Third International Humulus Symposium， Zatec， Czech Republic， Sept 9 14， 2012; ISHS： Leuven， Belgium， 2013.

[12]HASELEU G， INTELMANN D， HOFMANN T. Structure determination and sensory evaluation of novel bitter compounds formed fromacids of hop （Humulus lupulus L.） upon wort boiling[J]. Food Chem.， 2009， 116， 71-81.

[13]TANIGUCHI Y， MATSUKURA Y， OZAKI H， et al. Identification and quantification of the oxidation products derived from acids andacids during storage of hops （Humulus lupulus L.）[J]. J. Agric. Food Chem.， 2013， 61， 3121-3130.

[14]HASELEU G， INTELMANN D， HOFMANN T. Identification and RPHPLCESIMS/MS quantitation of bittertastingacids transformation products in beer[J]. J. Agric. Food Chem.， 2009， 57： 7480-7489.

[15]KROFTA K， VRABCOVA쫕 S， LISKOVA H. The method of preparation of pureacids[P]. CZ Patent 303，017， Jan 18， 2012.

[16]JASKULA B， AERTS G， DE COOMAN L. Hop acids isomerization and utilisation： an experimental review[J]. Cerevisia， 2010， 35： 57-70.

[17]HASELEU G， LAGEMANN A， STEPHAN A， et al. Quantitative sensomic profiling of hopderived bitter compounds throughout afullscale beer manufactoring process[J]. J. Agric. Food Chem.， 2010， 58： 7930-7939.

[18]JASKULA B， KAFARSKI P， AERTS G， et al. A kinetic study on the isomerization of hop acids[J]. J. Agric. Food Chem.， 2008， 56： 6408-6415.