Automatic and Intelligent Technologies of Solid-State Fermentation Process of Baijiu Production: Applications, Challenges, and Prospects
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foods Review Automatic and Intelligent Technologies of Solid-State Fermentation Process of Baijiu Production: Applications, Challenges, and Prospects Hong Ye 1,2 , Juan Wang 1,2, Jie Shi 1,2, Jingyi Du 1,2, Yuanhao Zhou 1,2, Mingquan Huang 1,* and Baoguo Sun 2,* 1 Key Laboratory of Brewing Molecular Engineering of China Light Industry, Beijing Technology and Business University, Beijing 100048, China; [email protected] (H.Y.); [email protected] (J.W.); [email protected] (J.S.); [email protected] (J.D.); [email protected] (Y.Z.) 2 Beijing Laboratory of Food Quality and Safety, Beijing Technology and Business University, Beijing 100048, China * Correspondence: [email protected] (M.H.); [email protected] (B.S.); Tel./Fax: +86-10-68985382 (M.H.) Abstract: Baijiu is the national liquor of China and the world’s most consumed spirit, which is produced using a unique and traditional solid-state fermentation (SSF) process. The development of an automatic and intelligent technology for SSF is more difficult than that for liquid-state fermentation. However, the technological upgrading of the SSF process is crucial for reducing the labor intensity, saving manpower, avoiding the waste of materials and energy, and providing a favorable operation environment for workers; moreover, it provides a great reference value to similar industries. This article reviews the latest application progresses in automatic and intelligent technologies for Baijiu Citation: Ye, H.; Wang, J.; Shi, J.; Du, production. The important technical processes are introduced successively, including the production J.; Zhou, Y.; Huang, M.; Sun, B. of Jiuqu, SSF, solid-state distillation, storage, and blending. The bottlenecks and challenges are Automatic and Intelligent pointed out for automatic and intelligent upgrading of these technical processes. Furthermore, the Technologies of Solid-State Fermentation Process of Baijiu typical technology application cases in an integrated automatic production line of Baijiu are also Production: Applications, Challenges, summarized. Next, the industrial development status of Baijiu production is compared with those of and Prospects. Foods 2021, 10, 680. other liquors in the world. Finally, future development directions are proposed. This review will https://doi.org/10.3390/ provide an overall introduction and objective analysis of recent developments and current challenges foods10030680 in Baijiu manufacturing so as to promote the intelligent brewing of Baijiu. Academic Editors: Christian Coelho Keywords: Baijiu; automatic technology; intelligent technology; solid-state fermentation; solid- and Chloé Roullier-Gall state distillation Received: 11 February 2021 Accepted: 12 March 2021 Published: 23 March 2021 1. Introduction Baijiu is the national liquor of China; with a 2000-year history, it is one of the oldest Publisher’s Note: MDPI stays neutral distilled liquors in the world. Baijiu is the world’s most-consumed spirit; for example, with regard to jurisdictional claims in the gross sales of Baijiu in 2019 were more than $80 billion [1]. Furthermore, it is very published maps and institutional affil- famous not only in China but also in other countries worldwide [2]. Baijiu, brandy, whisky, iations. vodka, gin, and rum are considered as six of the most famous distilled liquors manufac- tured worldwide [3]. According to the flavor characteristics, Baijiu can be classified into 12 flavor styles: Nong- (strong), mild (light), Jiang- (soy sauce), Mi-, Feng-, Chi-, Te-, herbal, Fuyu-, sesame, Laobaigan-, and Jian- (Nongjiang-) flavor types. The Nong-flavor type is Copyright: © 2021 by the authors. the most important representative of the Baijiu flavors followed by the mild flavor. As Licensee MDPI, Basel, Switzerland. the production processes shown in Figure1, the raw materials are mixed with whole or This article is an open access article powdered grains and are then wetted and cooked. Then, the mixture in a solid state is distributed under the terms and cooled to the appropriate temperature (about 18–35 ◦C), mixed with Jiuqu (Koji), and conditions of the Creative Commons placed in a fermentation jar or pit. When the fermentation is finished, the fermented grains Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ remaining in the solid state are removed for distillation to obtain the base liquor. After a 4.0/). long storage period followed by blending, the commercial liquor can be obtained. Foods 2021, 10, 680. https://doi.org/10.3390/foods10030680 https://www.mdpi.com/journal/foods Foods 2021, 10, x FOR PEER REVIEW 2 of 24 Foods 2021, 10, 680 2 of 23 in the solid state are removed for distillation to obtain the base liquor. After a long storage period followed by blending, the commercial liquor can be obtained. Figure 1.1. TraditionalTraditional production production processing processing of of Baijiu Baijiu (Image (Image reprinted reprinted from from ref. ref. [3], Copyright[3], Copyright (2018), (2018), with with permission permission from from ACS). American Chemical Society). As shown in Figure Figure 11,, itit represents aa traditionaltraditional solid-statesolid-state fermentationfermentation (SSF)(SSF) processprocess that all ofof thethe materialsmaterials during during transportation, transportation, mixing, mixing, fermentation, fermentation, distillation, distillation, and and reuse re- useare solid.are solid. Almost Almost all of all the of famous the famous high-quality high-quality Baijiu Baijiu brands brands in China in China are produced are produced using usingSSF, except SSF, forexcept the Mi-for andthe Mi- Chi-flavor and Chi-flavor Baijiu. In Baijiu. contrast, In othercontrast, distilled other liquors distilled worldwide liquors worldwideare generally are the generally products the of products liquid-state of liquid-state fermentation fermentation (LSF). (LSF). SSF is moremore challengingchallenging than than LSF LSF for for the the following following reasons. reasons. First, First, from from the the perspective perspec- tiveof material of material transportation, transportation, the efficiency the efficiency of the of conveying the conveying equipment equipment for solid for materialssolid mate- is rialsnot as ishigh not as as high that ofas a that pump of fora pump liquid for transportation. liquid transportation. Second, from Second, the perspectivefrom the perspec- of heat tivetransfer, of heat the transfer, heat exchange the heat among exchange solid amon materialsg solid is more materials difficult is more than indifficult liquids. than Thus, in liquids.the temperature Thus, the distribution temperature in distribution solid materials in solid is often materials not uniform, is often not making uniform, the productmaking thequality product unstable. quality This unstable. is especially This is evident especial duringly evident the processesduring the of processes Daqu production of Daqu pro- and ductionSSF. Third, and becauseSSF. Third, the because required the temperature required temperature variation for variation SSF is slowfor SSF and is moderate,slow and moderate,the traditional the traditional fermentation fermentation containers containers (such as pits (such or earthenware as pits or earthenware jars) are usually jars) are set usuallyunderground. set underground. As such, it As is difficultsuch, it is to difficult monitor to their monitor fermentation their fermentation parameters, parameters, resulting resultingin a “black in box”a “black fermentation box” fermentation process. proce Fourth,ss. Fourth, most of most the processes of the processes in the production in the pro- ductionof Baijiu of (e.g., Baijiu fermentation, (e.g., fermentation, distillation, distillation, and storage) and arestorage) batch operations,are batch operations, in which the in whichmaterials the requirematerials manual require operations manual operations and a long an residenced a long residence time. As atime. result, As ita result, is difficult it is difficultto apply to unified apply modernunified modern food processing food proc equipmentessing equipment and automatic and automatic production production lines to linesthe manufacture to the manufacture of Baijiu. of Nevertheless,Baijiu. Neverthele duringss, during the last the decade, last decade, there havethere beenhave greatbeen greatdevelopments developments in the automationin the automation and intellectualization and intellectualization of Baijiu of manufacturing. Baijiu manufacturing. It is a pity It isthat a pity few that reports fewhave reports focused have onfocused the advances on the advances in this area. in this area. In this paper, recentrecent advancesadvances in in the the automatic automatic and and intelligent intelligent manufacturing manufacturing of of Baijiu Bai- jiuare are reviewed reviewed comprehensively comprehensively and and critically critically in orderin order to provideto provide an overallan overall introduction introduc- tionand objectiveand objective analysis analysis of Baijiu of Baijiu manufacturing manufacturing for international for international and domesticand domestic engineers engi- neersand other and relevantother relevant persons. persons. It also It has also important has important reference reference value for value the manufacturingfor the manufac- of turingother distilled of other liquorsdistilled and liquors similar and products similar products produced produced using SSF. using SSF. 2. Production of Jiuqu Jiuqu is a type of fermentation starter; it is China-specific, and it includes Daqu, Xi- aoqu,