food and bioproducts processing 9 0 ( 2 0 1 2 ) 392–398

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Food and Bioproducts Processing

j ourna l ho me p age: www.elsev ier .com/ locate / fbp

Optimization of the distillation process of Chinese liquor bycomprehensive experimental investigation

Hailong Lia, Weixing Huanga,∗, Caihong Shenb, Bin Yib

a School of Chemical Engineering, Sichuan University, Chengdu 610065, Chinab Key Laboratory of Liquor Making Bio. Tech. & Appl. of Sichuan Province, Luzhou 646000, China

a b s t r a c t

Systematic experiments were carried out to optimize the distillation process of Chinese liquor through an

industrial-scale distiller. Effect of the operation conditions on the yield and quality of the liquor, and varia-

tion of liquor components during distillation were investigated. The steam flowrate of 1.60 kg/min gives the best

yield and quality, suggesting there exists an optimal flowrate for the distillation. The yield and quality of the

liquor drops down obviously with the increase of bulk density, implying that the fermented grains should be

loosely packed. Increasing the bed height from 600 to 1250 mm enhances the yield and quality, indicating that

current distiller (commonly used bed height from 700 to 900 mm) has great potential of improvement. Adding

small amount of edible alcohol in the steam boiler is proven to increase the liquor yield, but excess amount

causes the quality degraded sharply. The liquor-vapor leaking is found to commonly occur at the initial stage

of distillation process and dramatically decrease the yield and quality. A simple method is proposed to elimi-

nate the leaking effectively. The gas chromatography analysis results show that the variation of flavor compounds

during distillation is closely related to their dissolving properties in ethanol.

© 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Keywords: Chinese liquor; Distillation; Optimization; Steam flowrate; Bulk density; Bed height

To optimize the distillation process, the following fac-

1. Introduction

Chinese liquor is a popular alcoholic beverage with a con-sumption of more than 4 million kilograms and sale revenue ofabout 500 billion Chinese Yuan (CNY) each year (China BrewingIndustry Association and China Alcoholic Drinks IndustryEditorial Board, 2008). According to the aroma characteristics,Chinese liquor can be generally divided into five styles: thestrong aroma style, light aroma style, sauce aroma style, ricearoma style and miscellaneous aroma style (Fan and Qian,2006a). The manufacturing of Chinese liquor consists of threeconsecutive processes: fermentation, distillation and blend-ing. The fermentation is typically operated at 28–32 ◦C for afew months under anaerobic conditions in a solid state. After-wards, the fermented grains are distilled with steam to extractethanol and other flavor compounds. Finally, after being agedfor a period of time, these distillates are blended to yield the

final product. The distillation plays a critical role to link the

∗ Corresponding author. Tel.: +86 28 85405209; fax: +86 28 85403397.E-mail address: hwx@scu.edu.cn (W. Huang).Received 27 March 2011; Received in revised form 29 August 2011; Acc

0960-3085/$ – see front matter © 2011 The Institution of Chemical Engidoi:10.1016/j.fbp.2011.12.005

initial fermentation with the final blending. The goal of dis-tillation is to extract the flavor compounds in the fermentedgrains. Therefore, the distillation process determines the yieldand quality of the final product. For a long time, the researchon Chinese liquor has been mainly focused on the species ofmicroorganism and the formations of flavor compounds dur-ing the fermentation process (Shi et al., 2009; Xiang et al.,2005; Zhang et al., 2005) and focused on the qualitative andquantitative analysis of the components in the final prod-ucts (Fan and Qian, 2006a, 2006b; Zhu et al., 2007). However,the distillation process has been less investigated and cur-rently applied distillation operation still follows the way thatit has been done in ancient time. Therefore, the investiga-tion of distillation process and improvement of its efficiency isan important subject in the present development of Chineseliquor.

epted 19 December 2011

tors are important to be considered: (1) The steam flowrate,

neers. Published by Elsevier B.V. All rights reserved.

food and bioproducts processing 9 0 ( 2 0 1 2 ) 392–398 393

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keeping the steam flowrate fixed at 1.60 kg/min, and with-out any added edible alcohol. The grains were loaded with

Fig. 1 – Schematic diagram of the experimental distiller (1:steam pipe; 2: steam boiler; 3: steam distributor; 4: barrel;

hich represents the heating rate and convective strength,as important influence on the distillation process. In theresent production, the steam flowrate has not been defi-itely quantified, yet is mainly dependent on the intuitionf the operating workers. The random choice of the steamowrate leads to low distillation efficiency and great difficulty

n maintaining the stability of the yield and quality of theiquor. Only 55–75% of the ethanol in the fermented grainsan be effectively distilled out (Pu, 2005a). The extraction effi-iencies for ethyl acetate, ethyl butanoic, ethyl hexanoatend ethyl lactate, which are the most important flavor com-ounds in the strong aroma style liquor, have been found toe only about 8.5%, 3.5%, 30% and 10%, respectively (Chent al., 2009). Some researchers point out that slower heatingate is favorable for the distillation process (Pu, 2005a; Want al., 1998; Zhong et al., 2008), while the quantitative rela-ions between the yield and quality of the liquor and steamowrate have not been clearly known. Therefore, it is neces-ary to experimentally investigate the effect of steam flowraten the yield and quality of the liquor. (2) The bulk densitynd bed height of fermented grains: The bulk density, closelyelated to the porosity, determines the resistance of steamow and the areas for mass and heat transfer. Therefore, theulk density certainly affects the distillation products. Theulk density is much dependent on the mode of loading therains. Accordingly, understanding of the effect of the bulkensity is meaningful for the design of the loading mechani-al device. However, there have been few reports about thisactor thus far. The current used bed height of fermentedrains is 700–900 mm, which is determined according to theeight of operational worker, but not by the distillation pro-ess itself. Pu (2005b) has pointed out that the increase of bedeight leads to a gradual increase in the liquor yield of pernit mass of fermented grains. However, the research is lim-

ted to the bed height lower than 1000 mm. The circumstanceor the bed height beyond 1000 mm is seldomly reported asar as we know. (3) The cross-steaming technique: Du andong (2004) and Zhang et al. (2003) have proposed that theross-steaming by adding edible alcohol in the steam boiler isn effective technique to enhance the liquor yield. However,he relationship between the liquor quality and the addition

ount of edible alcohol is poorly known. (4) The liquor-vaporeaking: Water sealing has been used to joint the parts ofhe liquor distiller for a long time because of its easy opera-ion and low-cost, while the liquor-vapor usually leaks duringhe distillation process, especially in the initial stage. Theistillate obtained at the initial distillation stage has beenemonstrated to be high quality product (Li et al., in press),o the leaking may leads to the loss of high quality productsheoretically. However, there is not experimental report abouthe effect of the leaking on the yield and quality and no effec-ive method has been developed to eliminate the leaking upo now.

In this work, systematic experiments were carried out inn industrial-scale distiller to investigate the effect of steamowrate, bulk density, bed height, cross-steam technique and

iquor-vapor leaking on the yield and quality of the strongroma style liquor, and the variations of flavor compoundsuring distillation process. As a typical representation of Chi-ese liquor, the strong aroma style liquor takes up about0% of the total production (Shi et al., 2007). The findingsn this work also have important reference for other aroma

iquors on account of the essential similarity of the distillationrocesses.

2. Experimental

2.1. Experimental setup

A schematic diagram of the experimental distiller used inthis study is shown in Fig. 1. It consists of a steam supplypipe, a steam boiler, a steam distributor, a barrel for the fer-mented grains, a lid, a liquor-vapor tube and a condenser forthe liquor-vapor. The linkage between the steam boiler andbarrel is packing seal, and the other points are sealed by water.The experimental distiller is in industrial-scale, where theinner diameter and height of the barrel are 1000 and 1250 mm,respectively.

2.2. Experiment design

All the fermented grains used in this work were taken from theproduction field of a famous company for brewing the strongaroma style liquor. The grains were proportionally mixed witha little rice hull according to the production technology. Whenthe barrel was full of the mixed fermented grains, primarysteam was introduced into the steam boiler to produce moredurative and even secondary steam. The secondary steamwent through the distributor to heat the grains. The liquor-vapor flowed out of the grain bed and was condensed to bethe distillation products. The experiments were performedwith the secondary steam flowrate from 1.20 to 3.30 kg/min,the bed height from 600 to 1250 mm and the bulk density of389.7, 443.2 and 557.6 kg/m3. The method to determine thesecondary steam flowrate is to measure the flowrate of thecondensates after a long distillation time.

The effect of the steam flowrate were investigated at sixlevels of the flowrates, i.e., 1.20, 1.60, 1.90, 2.30, 2.50 and3.30 kg/min, with keeping the bed height and bulk densityfixed at 1250 mm and 389.7 kg/m3, respectively, and with-out any added edible alcohol. The effect of the bulk densitywere considered at three levels of the densities, i.e., 389.7,443.2 and 557.6 kg/m3, with keeping the bed height and steamflowrate fixed at 1250 mm and 1.60 kg/min, respectively, andwithout any added edible alcohol. The different bulk densi-ties were obtained from different loading methods: (1) dropthe grains into the barrel layer by layer; (2) drop the grainsinto the barrel from the upper edge of the barrel; and (3)drop the grains and shake the barrel simultaneously. Theeffect of the bed height were studied at seven levels of theheights, i.e., 600, 700, 800, 900, 1000, 1100 and 1250 mm, with

5: lid; 6: liquor-vapor tube; 7: condenser; 8: outlet of thecondenser; 9: sampling bottle).

394 food and bioproducts processing 9 0 ( 2 0 1 2 ) 392–398

distillation stages. The dimensionless concentrations (C1)reflect the changes of the concentrations of flavor compounds

the layer by layer mode, and the bulk density was in therange of 389.7–405.5 kg/m3 (higher bed with larger density).The effect of the cross-steaming technique were discussedat five volume levels of edible alcohol, i.e., 0, 2, 4, 6 and 8 L,with keeping the bed height, steam flowrate and bulk densityfixed at 1250 mm, 1.60 kg/min and 389.7 kg/m3, respectively.The added edible alcohol is composed of ethanol and water,in which the ethanol concentration is 95% by volume.

The distillates were continuously collected through thewhole distillation process. The distillate samples were dividedinto two parts based on their ethanol concentrations in linewith the actual production: the distillates with ethanol con-centration higher than 45% by volume were the effectiveproducts, while those with ethanol concentration lower than45% by volume were the non-effective products for poor qual-ity. The yield and quality of effective products are employedas the criterions for the distillation assessment and the effec-tive products are called ‘liquor’ for short in this study. All thedistillation experiments were twice repeated and the resultswere expressed as mean data.

In order to better present the variation of flavor compoundsduring the distillation process, the dimensionless concentra-tions C1 defined as C1 = ci,t/c̄i,t is introduced, where ci,j is theconcentration of one specific flavor compound i in the dis-tillates obtained at j distillation time period and c̄i,t is thearithmetic average value of ci,j. To express the effect of additionamount of edible alcohol into the boiler on the concentrationsof flavor compounds in the liquor, the dimensionless concen-trations C2 is adopted. The definition of C2 (C2 = ci,V/c̄i,V ) issimilar to that of C1, where ci,V is the concentration of fla-vor compound i in the liquors obtained at different additionamounts of edible alcohol in the steam boiler (V = 0, 2, 4, 6and 8 L) and c̄i,V is the arithmetic average value of ci,V. Thedimensionless concentrations of the important flavor com-pounds in the strong aroma style liquor were calculated, suchas, 1-propanol, 1-butanol, isobutanol, 1-hexanol, ethyl acetate,ethyl butanoic, ethyl hexanoate, ethyl lactate, acetic acid andhexanoic acid.

2.3. Chemical and sensory analysis

Ethanol concentration was determined by a density meter(DMA 5000, Anton Paar, Graz, Austria), based upon the rela-tionship between the density of water–ethanol mixtures andthe concentration of ethanol in the water–ethanol mixtures.An Agilent 6980 N (America) gas chromatography fitted witha flame ionization detector (FID) and a HP-INNOWax columnof 60 m × 0.25 mm × 0.25 �m (Hewlett-Packard, Palo Alto, CA)were used to quantify the flavor compounds. The experimentwas carried out at constant pressure, using nitrogen with theflowrate of 1.8 ml/min as the carrier gas. Each concentratedsample was injected at a split ratio of 1:50. The column tem-perature was firstly programmed at 40 ◦C for 4 min, followed byincreases of 2.5 ◦C/min to 60 ◦C and then 25 ◦C/min to 120 ◦C,and increased from 10 ◦C/min to 240 ◦C, and held at 240 ◦C for4 min. Injector and detector temperatures were 240 ◦C. Theanalyses were performed in three replications.

The sensory quality was evaluated in duplicate by two well-trained experts. They had more than 10 years experience in thesensory analysis for Chinese liquor. Sensory attributes, includ-ing taste, smell and aftertaste, were evaluated using a 10 point

hedonic scale, where 1 means dislike extremely and 10 meanslike extremely.

3. Results and discussion

3.1. Effect of the steam flowrate on the yield andquality of the liquor

Fig. 2 shows the effect of the steam flowrate qm on the liquoryield m and quality. The yield in the study is calculatedbased on 100 kg fermented grains, in which the concentra-tion of ethanol is 60% by volume. As can be seen fromFig. 2(a), increasing the steam flowrate from 1.20 to 1.60 kg/minenhances the yield of the liquor, but with further increasingthe flowrate, the yield turns to decrease, especially after thesteam flowrate exceeds to 2.30 kg/min. This phenomenon maycome down to the thermodynamics and mass transfer dur-ing the distillation process. The lower steam flowrate cannotprovide the thermal condition for full evaporation of ethanolin the fermented grains, while the higher flowrate causesthe grains to be pasted so that the mass diffusion withinthe grains become slower. Both situations results in lowerliquor yield. Differently, with the increase in steam flowrate,a single decreasing trend for the yield was reported by someresearchers (Pu, 2005a; Wan et al., 1998). This may be due tothat their experimental conditions are limited to high steamflowrates, not covering low steam flowrates. It can be observedfrom Fig. 2(b) that the liquor distilled with the steam flowrateof 1.60 kg/min possesses the best quality. Therefore, from theviewpoints of higher yield and better quality, there exists anoptimal steam flowrate for efficient distillation.

The liquor quality is mainly dependent on the concentra-tions of flavor compounds. Table 1 gives the concentrationsof representative flavor compounds in the strong aroma typeliquor distilled from different steam flowrates. The ethanolconcentration shows an upgrade tendency with the increaseof steam flowrate from 1.20 to 1.60 kg/m3, while it turns todecrease for further increasing the flowrate. Furthermore, thechange of the concentration of flavor compounds presentsclose relationship with the dissolving properties in ethanol.The concentrations of alcohol-soluble compounds, such as 1-propanol, 1-butanol, ethyl acetate, ethyl butanoic and ethylhexanoate, exhibit similar trends with that of ethanol, whilethe concentration of water-soluble compounds, such as ethyllactate, acetic acid and hexanoic acid, are opposite to that ofethanol.

Fig. 3 shows the dimensionless concentrations of flavorcompounds (C1) in the distillates obtained from different

Fig. 2 – Effect of the steam flowrate (qm) on the liquor yield(m) and quality.

food and bioproducts processing 9 0 ( 2 0 1 2 ) 392–398 395

Table 1 – Effect of the steam flowrate on the concentrations of the flavor compounds (g/L).

Compounds Steam flowrate, qm (kg/min)

1.20 1.60 1.90 2.30 2.50 3.30

Ethanol (%v/v) 61.008 66.322 65.875 62.322 59.123 53.3241-Propanol 1.144 1.645 1.922 1.498 1.287 1.1321-Butanol 2.425 2.584 2.816 2.676 2.380 2.128Isobutanol 0.393 0.513 0.473 0.413 0.362 0.3971-Hexanol 2.668 3.290 3.127 2.644 2.226 1.903Ethyl acetate 17.367 19.167 18.815 16.024 13.128 10.255Ethyl butanoic 5.591 5.844 5.713 5.523 5.213 4.804Ethyl hexanoate 39.290 42.042 40.126 38.930 37.747 35.834Ethyl lactate 52.759 44.233 50.081 55.438 58.785 63.811Acetic acid 4.302 4.250 4.350 4.422 4.5061 4.679Butanoic acid 2.844 2.858 3.011 3.165 3.297 3.350Hexanoic acid 6.566 6.504 6.960 7.898 8.929 9.058

Values are presented as mean of three replicates.

dtpiititcctc

3y

TDepsilaiitafl

Ft

Fig. 4 – Effect of the bulk density (�) on the liquor yield (m)and quality.

uring the distillation process. As can be seen from Fig. 3,he dimensionless concentrations of alcohol-soluble com-ounds gradually decrease during the distillation process,

ndicating the concentrations of alcohol-soluble compoundsncrease gradually during the distillation process; whilehose for water-soluble compounds exhibit increased trends,mplying increased concentrations during the process. Also,he different decreasing/increasing rates for these alcohol-ompounds/water-compounds can be attributed to differentompatibility with ethanol. The result implies that the varia-ions of flavor compounds during the distillation process arelosely related to their dissolving properties in ethanol.

.2. The relationship between the bulk density and theield and quality of the liquor

he fermented grains are compressible to a certain extent.ifferent loading modes result in different bulk densities. Theffect of the bulk density on the liquor yield m and quality isresented in Fig. 4, in which �1, �2 and �3 denote the bulk den-ity of 389.7, 443.2 and 557.6 kg/m3, respectively. The increasen the bulk density leads to a steady downward trend of theiquor yield. The quality attributes including taste, smell andftertaste, also exhibit gradual reduction tendency with thencrease of bulk density. This may be due to the fact that thencrease in bulk density leads to the increase of the resis-ance for steam flow, and the decrease of the areas of heat

nd mass transfer, which is unfavorable for the diffusion ofavor compounds.

ig. 3 – Variations of the dimensionless concentrations ofhe flavor compounds during the distillation process.

The concentrations of flavor compounds in the liquors dis-tilled at different bulk densities are analyzed and the resultsare shown in Table 2. It can be seen from this table that theconcentrations of flavor compounds gradually decrease withthe increase of bulk density, which can be attributed to theincrease of diffusion resistance. The decrease of the concen-tration of flavor compounds may explain the degradation ofthe quality. The results indicate that the operation of loadingthe fermented grains should be aimed at forming loosely bed,which is an important consideration for the design of loadingequipment.

Table 2 – Effect of the bulk density on the concentrationsof the flavor compounds (g/L).

Compounds � (kg/m3)

389.7 443.2 557.6

1-Propanol 1.645 1.535 1.2801-Butanol 2.584 2.403 2.052Isobutanol 0.513 0.440 0.3261-Hexanol 3.290 2.897 2.338Ethyl acetate 19.167 16.555 13.525Ethyl butanoic 5.844 5.669 5.104Ethyl hexanoate 42.042 39.324 36.016Ethyl lactate 53.902 48.367 44.233Acetic acid 4.585 4.432 4.250Butanoic acid 3.281 3.046 2.858Hexanoic acid 8.953 7.604 6.504

Values are presented as mean of three replicates.

396 food and bioproducts processing 9 0 ( 2 0 1 2 ) 392–398

Fig. 5 – Effect of the bed height (H) on the liquor yield (m) Fig. 6 – Effect of the cross-steaming on the liquor yield (m)and quality.

and quality.

3.3. Effect of the bed height on the yield and quality ofthe liquor

At different bed heights, the amounts of the fermentedgrains used in the distillation are obviously different (183 kgat 600 mm, 214 kg at 700 mm, 245 kg at 800 mm, 280 kg at900 mm, 312 kg at 1000 mm, 347 kg and 1100 mm and 397 kgat 1250 mm). For reasonable comparison, the liquor yieldsper 100 kg fermented grains obtained at different bed heightsare shown in Fig. 5(a). The increase in the bed height from600 to 1250 mm leads to steady enhancement in the liquoryield (Fig. 5(a)). This may be due to the fact that higher grainbed provides longer flow-path for steam, which benefits forthe accumulation of ethanol to produce effective products(ethanol concentration higher than 45% by volume). It can alsobe observed from Fig. 5(a) that the increasing rate of liquoryield is slowed, especially after 1100 mm. This may be due tothe fact that as the ethanol accumulates in steam, the differ-ence of ethanol concentrations between the fermented grainand the steam become smaller, so that the transport of ethanolfrom the grains to the steam becomes slower. The liquor qual-ity is continuously enhanced with the increase of bed heightfrom 600 to 1250 mm (Fig. 5(b)). When the bed height increasesfrom the present 800 mm (the bed height currently used inindustrial operation) to 1250 mm, the yield is enhanced about30%, implying that there exists great potential for the improve-ment of current distillation equipment. It should be pointedout that high bed height leads to labor-intensive operation ofloading the fermented grains. To reduce the labor intensity ofloading operation, it is essential to explore suitable mechani-cal equipment to achieve the loading process.

Table 3 shows the concentrations of flavor compoundsin the liquors distilled from different bed heights. Thealcohol-soluble compounds present a positive growth with theincrease of bed height, while the water-soluble compoundsexhibit a negative growth. The results once again show thatthe variations of flavor compounds during the distillationhave close relationship with their dissolving properties inethanol.

3.4. The cross-steaming technique and its effect on theyield and quality of the liquor

Five levels of edible alcohol with the volume of 0, 2, 4, 6 and8 L were added into the steam boiler to investigate the effect

of the cross-steaming technique on the yield and quality ofthe liquor. The liquor yield m is positively correlated with the

increase of the amount of added edible alcohol (Fig. 6(a)). Thechanges of the quality attributes (taste, smell and aftertaste)with the addition amount of edible alcohol exhibit two differ-ent trends: the quality of the liquor has inconspicuous changewhen a small amount of edible alcohol (<2 L) is added, while anexcess amount of added edible alcohol results in sharp degra-dation of liquor quality (Fig. 6(b)). Adding 6 L edible alcohol isfound to make the quality unacceptable.

To find the reason for the quality degradation, the dimen-sionless concentration (C2) of flavor compounds in the liquorsobtained with different addition amounts of edible alcoholis presented in Fig. 7. When a small amount of edible alco-hol (<2 L) is added, the dimensionless concentrations of flavorcompounds have not obvious change, suggesting that theconcentrations of flavor compounds keep almost constant;while for further increasing the addition amount, the dimen-sionless concentrations decrease remarkably, indicating sharpdecreased flavor compounds. The insignificant changes offlavor compound concentrations may explain inconspicuouschange of liquor quality when a small amount of edible alco-hol (<2 L) is added, and the degradation of the quality can beattributed to the remarkable decrease of the concentrationsof flavor compounds when excess amount of edible alcoholis added. Accordingly, it can be concluded that the cross-steaming technique could enhance the liquor yield and thekey is to determine appropriate addition amount of ediblealcohol.

Fig. 7 – Effect of the cross-steaming on the dimensionlessconcentrations of the flavor compounds.

food and bioproducts processing 9 0 ( 2 0 1 2 ) 392–398 397

Table 3 – Effect of the bed height on the concentrations of the flavor compounds (g/L).

Compounds H (mm)

600 700 800 900 1000 1100 1250

1-Propanol 1.042 1.187 1.254 1.376 1.492 1.569 1.6451-Butanol 1.680 1.925 2.016 2.173 2.407 2.525 2.584Isobutanol 0.221 0.290 0.337 0.372 0.414 0.476 0.5131-Hexanol 1.904 2.584 2.760 2.947 3.149 3.206 3.290Ethyl acetate 9.362 11.603 14.452 16.332 17.565 18.769 19.167Ethyl butanoic 4.668 4.903 5.337 5.557 5.640 5.752 5.844Ethyl hexanoate 33.324 35.644 37.685 39.020 40.373 41.830 42.042Ethyl lactate 58.756 55.788 53.081 49.446 46.648 44.580 44.233Acetic acid 4.804 4.674 4.550 4.473 4.382 4.275 4.250Butanoic acid 3.487 3.246 3.116 3.068 2.945 2.887 2.858Hexanoic acid 9.568 9.158 8.264 7.782 7.050 6.643 6.504

Values are presented as mean of three replicates.

3a

TsibtionsifldEtal

tsalltpvgswaottalEt

uynylb

Fig. 8 – Effect of the liquor-vapor leaking on the yield (m)

.5. The liquor-vapor leaking and its effect on the yieldnd quality of the liquor

he liquor-vapor is found to commonly leak from the water-ealing in the liquor distillation process, especially in thenitial stage. The distillates obtained in the initial stage haveeen verified to possess high quality (Li et al., in press), sohe liquor-vapor leaking may leads to the loss of high qual-ty products theoretically. However, study about the effectf the leaking on the yield and quality of the liquor hasot been experimentally reported. Even until now, there istill not effective method to eliminate the leaking. The exist-ng method of reducing leaking is to turn down the steamowrate once the leaking occurs. This method is just a reme-ial measure and cannot fundamentally eliminate the leaking.xperiments show that regulating the steam flowrate duringhe distillation process not only significantly affects the yieldnd quality of liquor, but also leads to instability of the distil-ation process.

Based on long-term experiment and analysis, we believehat the main cause for leaking is the temporary rise of pres-ure resulted from the trapped air in the distiller. The trappedir is in static state initially and incondensable, which givesarge resistance to the flow of liquor-vapor. Because of thearge resistance, the liquor-vapor cannot flow smoothly intohe condenser and will accumulate in the distiller so that theressure in the system increases temporarily until the liquor-apor arrives to the condenser at some time later. When theas pressure in the distiller surpasses the capacity of the waterealing, the liquor-vapor will leak. According to the analysis,e have used a blower to suck the trapped air in the distillert the initial distillation stage. This blower is connected to theutlet of the condenser by a transparent plastic tube. Oncehe liquor distillate appears at outlet of the condenser, therapped air can be considered to be completely sucked outnd the blower will be shut off. Then, the distillates at the out-et of condenser will be collected until the end of distillation.xperiment shows that the method is effective to eliminatehe leaking.

Fig. 8 is the comparative experiments results, which issed to explore the quantitative effect of the leaking on theield and quality of the liquor. When the leaking is elimi-ated, liquor yield increases dramatically from (the averageield of) 6.07 kg to 6.36 kg. It reveals that the leaking would

ead to the yield of the liquor decreased by ∼5%. It also cane seen from Fig. 8 that the liquor obtained in the no-leaking

and quality of the liquor.

possesses much better quality, compared with the liquor pro-duced in the leaking one. This result suggests that the leakingresults in remarkable degradation of liquor quality. In con-clusion, the liquor-vapor leaking is observably unfavorable forthe liquor distillation, and eliminating the leaking can signif-icantly enhance the yield and quality of the liquor.

4. Conclusions

Comprehensive experiments were carried out in an industrial-scale distiller in order to optimize the distillation processof Chinese liquor. It is found that there exists an optimalsteam flowrate for efficient distillation of the liquor. For theexperimental distiller, the steam flowrate of 1.60 kg/min (bedheight = 1250 mm; bulk density = 389.7 kg/m3) results in max-imum liquor yield and best liquor quality. The yield andquality of the liquor obviously drops down with the increaseof bulk density, implying that the fermented grains shouldbe loosely packed. Increasing the bed height from 600 to1250 mm enhances the yield and quality of the liquor, indi-cating that current distiller (commonly used bed height from700 to 900 mm) has great potential of improvement. Addingappropriate amount of edible alcohol in the steam boilercan increase the liquor yield, but excess addition makes thequality degraded sharply. The liquor-vapor leaking dramati-cally brings down the yield and quality of the liquor. The maincause for the leaking is temporal rise of pressure resulted from

the trapped air in the distiller and a simple method is proposedto eliminate this leaking. The variations of flavor compounds

398 food and bioproducts processing 9 0 ( 2 0 1 2 ) 392–398

during the distillation process are found to be closely relatedto their dissolving properties in ethanol.

The industrial-scaled experiments in the study offer animportant direction for the practical production, especially forthe enhancement and improvement of distillation process andequipment.

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