Exogenous Impurities in Baijiu: Sources, Detection, and Safety Strategies

Abstract

Baijiu, China’s traditional distilled spirit, is produced through solid-state fermentation and distillation of grains, resulting in a highly complex chemical and sensory profile. However, exogenous impurities introduced via raw materials, water, equipment, packaging, or the surrounding environment pose significant challenges to both safety and quality. These impurities, including heavy metals, plasticizers, pesticide residues, mycotoxins, environmental pollutants, and un-authorized food additives, are associated with neurotoxicity, carcinogenicity, endocrine disruption, and sensory defects. This narrative review synthesizes current knowledge on their sources, reported concentration ranges in Baijiu (generally at trace µg/kg–mg/kg levels), analytical detection methods with sub-mg/kg sensitivity, and control strategies for these substances. Regulatory frameworks, including China’s standards, are critically assessed, with emphasis on gaps such as the lack of explicit limits for certain classes of impurities. Case studies of contamination incidents are discussed to illustrate practical risks and monitoring gaps. Emerging trends, including low- and zero-alcohol Baijiu, are also considered in relation to changing impurity profiles and detection requirements. Recommendations include tightening regulatory limits, adopting portable and real-time detection technologies, and promoting the development of “pure Baijiu” that meets international safety and quality expectations. Future research priorities center on high-resolution mass spectrometry, advanced real-time monitoring, and eco-friendly analytical solutions, ensuring that Baijiu maintains both cultural heritage and global competitiveness.

1. Introduction

Baijiu, a distilled spirit with over 2000 years of history, is a cultural and economic cornerstone in China, accounting for approximately 30% of global spirit consumption by volume [1,2]. Produced through solid-state fermentation of grains such as sorghum, rice, wheat, and barley, followed by distillation and aging in clay or wooden vessels, Baijiu is renowned for its diverse sensory profiles, including fruity, savory, and earthy notes [3].

Baijiu production involves complex processes, a lengthy production cycle, and multiple intricate steps, all of which increase the risk of introducing various impurities that may pose food safety concerns [4,5]. Based on their origin, these impurities can be classified into endogenous hazardous substances and exogenous impurities. Endogenous hazardous substances are those generated during brewing through microbial metabolism or chemical reactions and are harmful to human health, such as methanol and cyanide. Exogenous impurities, on the other hand, are introduced through raw materials, water, equipment, environmental factors, or improper production practices. These include heavy metals, plasticizers, pesticide residues, mycotoxins, and food additives [5]. Many of these compounds present serious risks, including neurotoxicity, carcinogenicity, and endocrine disruption, and can also cause sensory defects that reduce consumer acceptance [5,6].

Therefore, the detection and control of exogenous impurities in Baijiu is of great significance for promoting the high-quality development of the Baijiu industry. The global trend toward healthier beverages has further heightened these concerns. In particular, low-alcohol (≤20% ABV) and alcohol-free Baijiu products, often produced using vacuum distillation, may be more susceptible to the concentration of non-volatile impurities [7,8]. At the same time, the expansion of Baijiu into international markets requires strict compliance with global regulatory standards, such as the European Union’s maximum residue limits (MRLs) for pesticides under Regulation (EC) No 396/2005.

Although several studies have examined exogenous impurities in fermented beverages and in the Baijiu production process, there remains no comprehensive review that integrates sources, risks, reported concentration levels, detection methods, and control strategies specifically for exogenous impurities in finished Baijiu. Existing reviews often focus on flavor compounds and fermentation mechanisms, leaving a clear gap in synthesizing exogenous impurities-focused evidence across the entire production chain. Addressing this gap is essential given the increasing regulatory scrutiny, global market expansion, and rising demand for Baijiu products.

In this review, we summarize current knowledge on the sources, health risks, detection methods, and control strategies of exogenous impurities in Baijiu. Special emphasis is placed on analytical techniques, which provide sensitive and accurate detection at trace levels. Case studies, such as heavy metal contamination and pesticide residues in Baijiu, provide practical insights. The review also briefly considers the implications of low- and zero-alcohol Baijiu in changing impurity profiles, while maintaining focus on traditional Baijiu. The overall goal is to support the development of “pure Baijiu”—a concept emphasizing minimal harmful impurities and preserved sensory excellence—through stricter standards, advanced analytical detection, and sustainable production practices.

2. Sources, Risks, and Analytical Detection of Exogenous Impurities in Baijiu

2.1. Main Contaminants from Raw Materials

2.1.1. Pesticide Residues

Pesticide Residues in Raw Materials for Baijiu

Pesticide residues in Baijiu primarily originate from raw materials, posing potential safety concerns if not properly controlled. Pesticide residues persist in grains like sorghum and rice, transferring to Baijiu during distillation due to their thermal stability [4,9].

Recent investigations have provided a clearer understanding of their behavior during the production process. Chen et al. reported the detection of 12 types of pesticide residues across various production stages, with organochlorine and carbamate pesticides being most abundant in raw grains. After fermentation, levels of organochlorine and pyrethroid pesticides increased relative to others, while carbamate pesticides were found to dominate in the final distilled product. The study indicated that although pesticide residues were introduced early via raw materials and Daqu, both solid-state fermentation and distillation contributed significantly to residue reduction [10]. Complementing this, Bai et al. found that the steeping and steaming steps prior to fermentation already removed a considerable portion of pesticide residues, and fermentation further reduced residues ranging from 39.8% to 74.2% through microbial degradation. The distillation process was again shown to be particularly effective in minimizing residual pesticides in the final liquor [9].

During fermentation, the overserved reduction is strongly linked to microbial enzymatic activity. Solid-state fermentation microbiota—predominantly Aspergillus, Bacillus, Lactobacillus, and yeasts—express hydrolases and esterases capable of cleaving ester bonds in organophosphates and pyrethroids, generating more polar metabolites that are either further degraded or retained in the fermented grains. Carbamate pesticides are susceptible to microbial carbaryl hydrolases and amidases, whereas certain molds in Daqu produce oxidative enzymes that initiate dichlorination or hydroxylation of organochlorines. These mechanisms explain class-specific degradation behavior and the generally higher degradation rates of carbamates and organophosphates compared with more persistent pyrethroids and organochlorines.

Together, these findings highlight the importance of raw material control, microbial action, and thermal processing in mitigating pesticide contamination in Baijiu.

Quality Control and Detection

In China, the current regulation of pesticide residues related to Baijiu production is guided by GB/T 10781 [11], which references the maximum residue limits (MRLs) established for drinking water (GB 5749-2006) [12] and cereals (GB2763-2021) [13]. However, there are no specific national standards for pesticide residues in the finished Baijiu product, highlighting a gap in targeted safety oversight. Moreover, no international regulatory bodies such as EU and Codex specify MRLs for pesticide residues in Baiju.

Analytical detection of pesticide residues in Baijiu typically replies on gas chromatography–mass spectrometry (GC/MS) or liquid chromatography (LC)–mass spectrometry (LC/MS), which offer high sensitivity and accuracy. He et al. developed an LC-MS/MS method capable of simultaneously quantifying eight carbamate pesticide residues in Baijiu, achieving detection limits in the range of 0.5–10 µg/kg [14]. More recently, Chen et al. applied a modified QuEChERS sample preparation method combined with both GC-MS/MS and LC-MS/MS to detect 12 pesticide residues across different stages of strong-flavor Baijiu production [10]. The targeted compounds included organophosphorus (dimethoate, methyl parathion), organochlorine (lindane, clofenotane), carbamate (thiodicarb, carbofuran), pyrethroid (fenvalerate), and heterocyclic organic pesticides (metalaxyl, butralin, linuron, butachlor, carbendazim). The method achieved limits of detection at or below 0.05 mg/kg and was successfully validated across eight production stages, offering a comprehensive approach for monitoring pesticide residues in Baijiu production.

Control Strategies for Pesticide Residues in Baijiu Raw Materials

Given the bio-accumulative nature and high toxicity of many pesticides, it is essential to strictly control pesticide residues in raw materials used for Baijiu production. China’s ‘National food safety standard—Maximum residue limits for pesticides in food’ (GB2763-2021) specifies 10,092 maximum residue limits for 564 different pesticides across various food categories. This includes detailed MRLs for grains commonly used in Baijiu fermentation, such as sorghum, wheat, corn, and rice. Examples of commonly regulated pesticides and their corresponding residue limits are provided in

Table 1. Maximum residue limits (MRLs) of selected pesticides in grains (mg/kg).

Table	Paddy Rice	Sorghum	Rice	Wheat	Corn	Barley	Pea
Fenitrothion	5	5	1	5	5	5	0.5
Triadimefon	0.5	-	-	0.2	0.5	0.2	0.05
Permethrin	2	2	-	2	2	2	1
Parathion	0.1	0.1	0.1	0.1	0.1	0.1	0.1
Malathion	8	3	0.1	8	0.5	8	8
Isofenphos methyl	0.02	0.02	-	0.02	0.02	0.02	0.02
Triadimenol	0.5	0.1	-	0.2	0.5	0.2	-

.

Other than strictly controlling pesticide residues in raw materials used for Baijiu production, another important strategy is the development of dedicated grain production bases under direct oversight by Baijiu brewers. For example, major leading Baijiu brewers have increasingly established grain cultivation zones tailored specifically for brewing. Maotai Group has developed organic sorghum production areas in Guizhou Province, while Wuliangye Group has set up similar organic grain bases in Sichuan Province, cultivating glutinous red sorghum, glutinous rice, rice, corn and wheat [15,16]. These initiatives aim to promote the use of specialized, organic and traceable grains, thereby enhancing the safety, quality, and stability of raw materials used in Baijiu production and reducing reliance on external supply chains.

A portion of pesticide residues present in raw materials can be partially removed during the brewing process. For instance, soaking rice grains (steeping) effectively removes water-soluble pesticides, achieving a removal rate above 70%. The steaming step further promotes volatilization and thermal degradation, with degradation reaching up to 75.3%. During fermentation, microbial activities contribute to the biodegradation of residual pesticides, reducing levels by as much as 74.2%. Among all steps, distillation is the most effective, with degradation rates exceeding 90%, significantly minimizing pesticide residues in the final product [17]. These findings suggest that optimizing brewing parameters could further enhance the degradation or removal of pesticide residues from raw materials. However, many Baijiu brewers are reluctant to modify long-established techniques, as doing so would require significant financial and human resources, as well as extensive experimental validation to ensure that changes do not compromise product quality.

2.1.2. Mycotoxins

Mycotoxins in Raw Materials for Baijiu

Mycotoxins are toxic secondary metabolites produced by fungi during their growth and reproduction. In Baijiu, mycotoxins primarily originate from two sources. Firstly, they may be introduced through raw materials, as a result of adverse environmental conditions during crop cultivation, transportation, or storage. For instance, aflatoxin B₁ (AFB₁) and ochratoxin A (OTA) are produced by molds such as Aspergillus and Penicillium, and can contaminate grains stored under high humidity or poor sanitary conditions. Secondly, mycotoxins can be generated during fermentation, as secondary metabolites of filamentous fungi involved in the solid-state brewing process. Due to their thermal stability, some mycotoxins can survive distillation and accumulate in the final distillate [18,19].

China’s national standard GB 2761-2017 (Maximum levels of mycotoxins in Foods) specifies limit values for serval types of mycotoxins in food, including those relevant to grains used in Baijiu production [20]. Representative examples are listed in

Table 2. Maximum residue limits (MRLs) of mycotoxins in grains (μg/kg).

Type of Grain	Paddy Rice	Sorghum	Rice	Wheat	Corn	Barley	Pea
Aflatoxin B1 (AFB1)	10	5	10	5	20	5	-
Deoxynivalenol (DON)	-	-	-	1000	1000	1000	-
Ochratoxin A (OTA)	5	5	5	5	5	5	5
Zearalenone (ZEN)	-	-	-	60	60	-	-

.

Quality Control and Detection

The most common mycotoxins encountered during Baijiu production include AFB₁, OTA, and zearalenone (ZEN). Current detection methods for mycotoxins mainly include High-Performance Liquid Chromatography (HPLC), liquid chromatography–tandem mass spectrometry (LC-MS/MS), and enzyme-linked immunosorbent assay (ELISA). Among these, LC-MS/MS is the method specified in the industry standard LS/T 6133-2018, which is used for detecting 16 types of mycotoxins in major grains such as wheat and corn [21]. Liu Xiaoqing et al. developed a method using a pre-treatment extraction with an acetonitrile-0.1% formic acid aqueous solution (85:15, v/v) to isolate mycotoxins from fermented grain mash. The extracted samples were then analyzed using LC-MS/MS combined with external standard quantification to detect 31 different mycotoxins [22]. The results demonstrated accuracy, recovery and linearity. The method was suitable for the detection of mycotoxins in raw materials used for Baijiu production.

Control Strategies for Mycotoxins in Baijiu Raw Materials

The contamination level of mycotoxins in raw materials is closely related to multiple environmental factors, including moisture content, water activity, air humidity, temperature, and pH. It is difficult to remove mycotoxins through conventional processing techniques once contamination occurs. Several detoxification approaches have been developed, including physical, chemical and biological methods.

Physical methods commonly involve washing, adsorption, irradiation and heat treatment. For example, ultraviolet (UV) irradiation can degrade certain mycotoxins, based on their specific UV absorption spectra. AFB₁, for instance, has a maximum absorption at 265 nm. After 4 h of UV exposure, its degradation rate in rice can reach approximately 45% [23]. However, physical treatment often requires specialized equipment, consumes significant energy, and damages nutritional components of the material.

Chemical methods typically involve treatment with acids, alkalis, ammonia, or strong oxidizing agents. These chemicals de-stabilize the molecular structure of mycotoxins under extreme pH environment or oxidative conditions, leading to their break-down. However, chemical treatments may generate undesirable by-products and leave residual chemicals, posing risks of secondary contamination.

Biological methods make use of microorganisms to adsorb or degrade mycotoxins. For example, Juodeikiene et al. reported that lactic acid bacteria (LAB) could adsorb serval Fusarium mycotoxins in wheat, achieving removal rates of 23% for ZEN, 34% for DON, and 73% for T-2 toxin (T-2) and HT-2 toxin (HT-2) [24].

Despite their potential, none of these methods offer complete or universally applicable solutions, and each has limitations related to effectiveness, safety, or practicality. Therefore, the most effective way to control mycotoxin contamination in Baijiu production remains the strict inspection and quality control of raw materials.

2.1.3. Other Raw Material Issues

The safety of water is another important factor in Baijiu production. Water that comes into direct contact with raw materials, intermediates, or finished product can be divided into three main categories: brewing water (used in fermentation starter preparation, microbial cultivation, soaking of raw materials), washing water (used for cleaning equipment, tools, and production facilities), and dilution water (used for blending high-alcohol content Baijiu or diluting base liquor to produce lower alcohol products). Among these, dilution water is especially critical as it directly becomes part of the final product. To ensure safety and quality, dilution water must meet strict requirements for heavy metals: <0.1 mg/L in total, with specific thresholds for arsenic (<0.01 mg/L), cadmium (<0.005 mg/L), mercury (<0.001 mg/L), selenium (<0.01 mg/L), and lead (<0.01 mg/L) [25].

2.2. Main Contaminants from Packaging and Processing Materials

2.2.1. Heavy Metals

The Presence of Heavy Metals in Baijiu

In Baijiu, heavy metals of particular concern include lead (Pb), cadmium (Cd), Mercury (Hg), arsenic (As), and copper (Cu), due to their potential toxicity to human health [26,27]. These contaminants originate from two sources. The first is through raw materials and water used for Baijiu brewing, which may carry trace levels of heavy metals [4,28]. The amount of heavy metals introduced into Baiju through raw materials is typically very small. In a study on strong-aroma Baijiu, Li Yongjiao et al. investigated the migration of metal elements during the distillation process and found that less than 6% of the metal content was transferred into the distillate, while more than 94% remained in the fermented grains after distillation [29]. The second source arises from equipment and contact materials used during distillation, blending and storage [27,30]. Distillation equipment and storage contains may introduce metal elements such as iron (Fe), nickel (Ni), and aluminum (Al), as well as heavy metals like lead (Pb) and chromium (Cr), into Baijiu [29]. Among these, ceramic containers are a major contributor to heavy metal contamination in Baijiu [31]. Two critical factors influencing the leaching of metals from ceramics are pH and alcohol concentration [32,33]. Baijiu typically has a low pH. The acidic nature of Baijiu facilitates the dissolution of heavy metals from ceramic glazes [30,32,33]. However, ethanol can interact with glaze components to form low-solubility salts, which inhibit metal release. The higher the alcohol content is, the stronger the inhibition effect it has. Therefore, storing high-proof Baijiu in ceramic containers is generally more effective at minimizing heavy metal leaching [32,33,34].

Beyond regulatory thresholds, reported concentrations in commercial Baijiu provide a clearer picture of practical exposure levels. As summarized in Table 3, Cd concentration in Baijiu ranges from 0.75 to 19.55 µg/L, while Pb ranges from 0.35 to 580 µg/L, indicating greater variability in lead contamination across products. These findings highlight the importance of monitoring equipment and storage materials to control heavy metal exposure.

Detection of Heavy Metals in Baijiu

China’s national standard GB 2762-2022 ‘Food Safety Standard Maximum Levels of Contaminants in Foods’ specifies maximum residue limits for heavy metals in Baijiu, with an emphasis on strict limits for lead, set at 0.5 mg/kg [35]. Currently, there are no specific regulatory limits established for other heavy metals in Baijiu.

Currently, the primary methods for detecting heavy metals in Baijiu include graphite furnace atomic absorption spectrometry (GFAAS) and inductively coupled plasma mass spectrometry (ICP-MS). According to the national standard GB 5009.268-2025 ‘National Food Safety Standard-Determination of Multiple Elements in Food’, ICP-MS is specified for the quantification of heavy metals such as Pb, Cd, Hg and As in food products, including alcoholic beverages like Baijiu [36].

Control Strategies

The prevention and control of heavy metals in Baijiu production involves three critical measures. Firstly, strict quality control of raw materials and water is essential to keep heavy metal contaminants below regulatory limits. Secondly, the use of chemical-stable and food-grade storage equipment is necessary to minimize the risk of metal leaching during aging and storage. Thirdly, for heavy metals that have already migrated into the product, post-processing techniques such as adsorption can be applied to reduce their levels. For example, Wang et al. used nitric acid-modified activated carbon to oxidize surface functional groups, thereby enhancing the material’s selective adsorption capacity, ion-exchange ability, and affinity for metal ions. The study found that under ambient conditions, with an adsorption time of 8 h, activated carbon modified with nitric acid has demonstrated high efficacy in removing lead from Baijiu, achieving a removal rate of 96.7%, thereby offering a practical solution for targeted heavy metal reduction [37].

2.2.2. Plasticizers

The Presence of Plasticizers in Baijiu

Plasticizers are polymer additives, primarily referring to phthalate esters, which are widely used in industrial manufacturing to improve the flexibility and strength of plastic products [38,39]. In the Baijiu brewing process, plasticizers are mainly introduced through migration from raw materials, production equipment, and packaging materials. The most frequently detected phthalate (PAE) plasticizers in Baijiu include dibutyl phthalate (DBP), di(2-ethylhexyl) phthalate (DEHP), dimethyl phthalate (DMP), diethyl phthalate (DEP), and di-isobutyl phthalate (DIBP) [40].

Firstly, plasticizers accumulated in soil, water, or air can be absorbed by grains and carried into Baijiu through the brewing process [40]. Due to their semi-volatile nature, phthalates can transfer from raw materials into the distillate during distillation and ultimately enter the human body, where they may disrupt hormonal balance and lead to reproductive and development disorders.

Secondly, direct contact between Baijiu and materials containing phthalates during production and storage may result in further contamination [40]. This is considered the most significant source. Plastic components such as hoses, seals, or tanks may release plasticizers, especially when exposed to high-percentage alcohol content and prolonged contact times. Materials such as polyvinyl chloride (PVC) and polyethylene terephthalate (PET) show the highest migration levels.

Thirdly, plasticizers migrate from packaging materials [41]. Plastic bottle caps and inner seals can release plasticizers during storage and distribution. Packaging made from thermoplastic elastomers is particularly prone to migration. In addition, the extent of plasticizer migration is positively correlated with percentage of alcohol content, storage temperature and contact duration.

Detection of Plasticizers in Baijiu

Currently, commonly used methods for detecting phthalate plasticizers in Baijiu include GC, LC, MS, and GC-MS. In addition, several emerging rapid detection techniques have been developed, such as fluorescence assays, immunoassays, and electrochemical methods [40,42]. Wei Dong et al. applied a QuEChERS or vortex-assisted surfactant-enhanced-emulsification liquid–liquid micro-extraction (VSLLME) technique combined with GC-MS to analyze 14 types of phthalate plasticizers in raw materials (sorghum, wheat, rice and sticky rice) and 39 brands of Baijiu samples. Among the tested samples, 5 plasticizers (DBP, DEHP, DMP, DEP, DIBP) were detected in 100% of the samples. The detected concentrations in Baijiu ranged from 0.003 to 0.292 mg/kg [40].

Among these, GC-MS is the method officially specified in the national standard Determination of Phthalates in Food (GB 5009.271-2016).

Control Strategies

To strengthen the control of plasticizer contamination in alcoholic beverages, the State Administration of Market Regulation of China issued the Guidelines on Risk Prevention and Control of Plasticizer Contamination in Food in 2019 (Document No. [2019] 214). According to these guidelines, the concentrations of DBP and DEHP in Baijiu should not exceed 1 mg/kg and 5 mg/kg, respectively [43]. These regulatory thresholds provide a reference for quality monitoring and underscore the importance of routine plasticizer detection in Baijiu production.

To effectively mitigate plasticizer contamination in Baijiu, a series of preventive and control measures have been proposed. Firstly, it is essential to strengthen safety control over raw materials, minimizing the risk of contamination from the source. Secondly, Baijiu brewers are encouraged to upgrade production equipment, replacing plastic components with food-grade stainless steel—a practice commonly referred as ‘replacing plastic with steel’. Thirdly, the use of safer and more advanced packaging materials should be prioritized, with strict quality checks on bottle caps, inner seals, and liners. Moreover, systematic control across storage, transportation distribution and retail stages should be reinforced to prevent secondary contamination. Furthermore, plasticizer removal technologies such as adsorption techniques have shown promising results. For example, the application of Baijiu-specific activated carbon can achieve up to 81% removal of DBP, offering a practical solution for reducing residual plasticizers in the Baijiu final product.

In addition, recent research suggested that distillation itself may serve as an effective control point. In a study by Dong et al., the concentration of phthalate esters (PAEs) during Baijiu distillation showed a progressive decline, with the highest levels found in the distillate head, where PAE concentrations were 1.6 to 8.1 times higher than those in subsequent fractions (heart and tail distillates) [40]. These findings indicate that PAEs can be partially removed or controlled through distillation practices. This highlights the potential of distillation management, such as fractional collection and early fraction discarding, as a supplementary strategy in reducing PAEs in Baijiu.

2.3. Un-Authorized Food Additives—Sweeteners

2.3.1. The Presence of Sweeteners in Baijiu

Sweeteners are a major category of food additives used in Baijiu, and can enhance its smoothness and perceived sweetness, thereby improving sensory appeal [44]. In practice, illicit addition of sweeteners is often economically motivated. By improving perceived taste, brewers can increase consumer acceptance, boost sales, and sell lower-quality products at competitive prices while reducing production costs. These pressures are particularly relevant for smaller brewers, where financial incentives may encourage shortcuts that compromise product authenticity and safety. Prior to the enforcement of updated regulatory national standard GB 2760 in 2014, commonly used additives in Baijiu included sweeteners, flavoring agents, nutritional fortifiers, and processing aids. Among reported cases of excessive additive use, sweeteners are the most frequently detected un-authorized additives in Baijiu. According to national sampling and testing data, sodium cyclamate accounted for the highest proportion at 47%, followed by neotame (26%), saccharin sodium (21%) and sucralose (6%) [5]. While sodium cyclamate is widely used across the food and beverage industry, excessive intake has been associated with potential health risks such as negative impact on gastrointestinal, neurologic and cardiovascular systems [45].

Since the implementation of GB 2760-2014 ‘National Food Safety Standard for the Use of Food Additives’, the addition of any sweetener to Baijiu has been strictly prohibited. The current GB 2760-2024 standard maintains the provision established in GB 2760-2014, which explicitly prohibits the use of sweeteners in Baijiu [46]. However, recent violations reveal persistent challenges in regulatory compliance. For instance, in 2025, a batch of Baijiu produced by Gansu Pukang Liquor Group Co., Ltd. was found to contain sodium cyclamate [47]. In 2024, a batch of Baijiu produced by Zuiyuanchun Liquor Group Co., Ltd. was also found to contain sodium cyclamate [48]. The illegal addition of sweeteners is particularly prevalent in bulk Baijiu. For example, in Chongqing city, a total of 1776 Baijiu samples were collected between 2017 and 2020, among which 58 batches were found to contain unauthorized sweeteners. All of them were from bulk Baijiu products [49]. These incidents underscore the ongoing risk of illegal sweetener use in Baijiu and highlight the need for effective regulatory enforcement and greater awareness among Baijiu brewers to ensure product compliance and consumer safety.

2.3.2. Detection of Sweeteners in Baijiu

A variety of analytical methods have been established for the detection of sweeteners in food matrices including Baijiu. The Chinese national standard GB 5009.97-2023 specifies HPLC and LC-MS/MS as the official techniques for sweetener determination [50]. However, in recent years, LC-MS/MS has become the preferred method for the quantitative analysis of sweeteners in Baijiu, owing to its high sensitivity and strong compatibility with complex matrices.

Beyond the national standards, advanced techniques such as ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS) and ion chromatography (IC) have also been explored [51]. In particular, IC has shown promise for the detection of sodium cyclamate in Baijiu. By optimizing column separation conditions, IC achieves a broad linear detection range and eliminates the need for pre-column derivatization, which is typically required in LC protocols. Reported recovery rates range between 96% and 108%, indicating good analytical accuracy and reliability [52].

However, despite these advantages, the broader application of IC remains limited. The availability of suitable, specialized separation column is still restricted, and the method is highly sensitive to column variability, which can affect reproducibility. Consequently, while IC presents a valuable alternative for targeted applications, LC-MS/MS remains the most robust and widely adopted platform for both regulatory enforcement and research on sweetener monitoring in Baijiu.

In addition, Gu et al. introduced a pre-column derivatization-HPLC method with fluorescence detection as a cost-effective and sensitive alterative for sodium cyclamate determination. This method achieved a detection limit of 0.03 mg/kg and recoveries between 90.7% and 100.9%, with results consistent with those obtained using LC-MS/MS [53]. Such approaches highlight the potential of chromatographic methods beyond LC-MS/MS to improve accessibility and provide reliable results for Baijiu monitoring.

2.3.3. Control Strategies

Despite the clear prohibition of sweetener use in Baijiu under national food safety regulations, recent surveillance data from government sampling programs continue to report the occasional detection of sweeteners in commercial Baijiu products. These findings underscore the need for enhanced quality control measures and stricter regulatory compliance across the industry. Currently, routine surveillance relies on national standard methods, which, although they are highly accurate and standardized, are resource-intensive, requiring specialized laboratory instrumentation, skilled personnel, and extended processing time. These limitations restrict their scalability for widespread or high-frequency screening.

In this regard, emerging detection methods may offer practical support for regulatory enforcement. The development and implementation of rapid, cost-effective on-site detection technologies are critically needed. Such tools would significantly improve screening efficiency, enable real-time monitoring, and support more proactive enforcement of food safety regulations within the Baijiu production and supply chain.

Moreover, while analytical methods for detecting sweeteners exist, quantitation against allowable limits is unnecessary for Baijiu, as the presence of any sweetener is strictly prohibited and should be eliminated.

2.4. Reported Levels of Exogenous Impurities in Baijiu

Although extensive research has examined the sources, pathways, and detection methods of exogenous impurities in Baijiu, published data on their actual concentrations in commercial Baijiu remain limited. Existing studies primarily focus on raw materials, storage vessels, or simulated contamination scenarios, while systematic surveys of finished Baijiu, especially across different price tiers and production scales, are sparse. This lack of comprehensive datasets constrains risk assessment, slows regulatory progress, and contributes to uncertainty regarding true exposure levels among Baijiu consumers.

To highlight the current state of knowledge, Table 3 summarizes representative reported concentrations of major exogenous impurities measured in commercial Baijiu samples. The data illustrate that while contamination is generally controlled within regulatory limits, information gaps persist across several impurity classes, particularly for products outside the premium market. These gaps underscore the need for coordinated monitoring initiatives, harmonized reporting standards, and industry-wide surveillance programs capable of providing a comprehensive exogenous impurities profile for Baijiu.

Table 3. Concentrations of exogenous impurities in Baijiu.

Impurity Type	Sample Type/Location	Number of Samples	Concentration of Exogenous Impurities	Reference
Pesticide Residues	Strong-flavor Baijiu in China	10 groups	Lindane: 0.71–12.20 mg/kg Metalaxyl: 0.62–9.17 mg/kg Butachlor: 0.14–2 mg/kg Methyl parathion: 0.02–1.90 mg/kg Fenvalerate: 0.18–1.17 mg/kg Thiodicarb: 0–0.61 mg/kg Chofenotane: 0–0.39 mg/kg Linuron: 0.03–0.35 mg/kg Carbofuran: 0.03–0.06 mg/kg Dimethoate: 0–0.05 mg/kg	[10]
Mycotoxins	Obtained from Chinese market, including various flavors	43 samples	FB1: 0.25–0.31 μg/L FB2: 0.27–0.30 μg/L FB3: 0.41–0.48 μg/L ZEN: 3.69–5.11 μg/L DON: 1.81–12.75 μg/L	[18]
Heavy Metals	Locally distilled Baijiu obtained in rural central China	47 samples	Cadmium: 0.75–19.55 μg/L Lead: 0.35–580 μg/L	[34]
Plasticizers	20 Baijiu brands collected from various local markets (China)	39 samples	DMP: 0.05–0.12 mg/kg DEP: 0.04–0.05 mg/kg DIBP: 0.08–0.15 mg/kg DBP: 0.10- 0.18 mg/kg DEHP: 0.13–0.24 mg/kg	[40]
Sweeteners	12 Baijiu brands collected from various supermarkets (China)	30 samples	Sucralose (SCL): 0–8.45 mg/kg Neotame (NEO): 0–1.07 mg/kg Saccharin (SAC): 0–3.22 mg/kg	[54]

Table 3. Concentrations of exogenous impurities in Baijiu.

Impurity Type	Sample Type/Location	Number of Samples	Concentration of Exogenous Impurities	Reference
Pesticide Residues	Strong-flavor Baijiu in China	10 groups	Lindane: 0.71–12.20 mg/kg Metalaxyl: 0.62–9.17 mg/kg Butachlor: 0.14–2 mg/kg Methyl parathion: 0.02–1.90 mg/kg Fenvalerate: 0.18–1.17 mg/kg Thiodicarb: 0–0.61 mg/kg Chofenotane: 0–0.39 mg/kg Linuron: 0.03–0.35 mg/kg Carbofuran: 0.03–0.06 mg/kg Dimethoate: 0–0.05 mg/kg	[10]
Mycotoxins	Obtained from Chinese market, including various flavors	43 samples	FB1: 0.25–0.31 μg/L FB2: 0.27–0.30 μg/L FB3: 0.41–0.48 μg/L ZEN: 3.69–5.11 μg/L DON: 1.81–12.75 μg/L	[18]
Heavy Metals	Locally distilled Baijiu obtained in rural central China	47 samples	Cadmium: 0.75–19.55 μg/L Lead: 0.35–580 μg/L	[34]
Plasticizers	20 Baijiu brands collected from various local markets (China)	39 samples	DMP: 0.05–0.12 mg/kg DEP: 0.04–0.05 mg/kg DIBP: 0.08–0.15 mg/kg DBP: 0.10- 0.18 mg/kg DEHP: 0.13–0.24 mg/kg	[40]
Sweeteners	12 Baijiu brands collected from various supermarkets (China)	30 samples	Sucralose (SCL): 0–8.45 mg/kg Neotame (NEO): 0–1.07 mg/kg Saccharin (SAC): 0–3.22 mg/kg	[54]

3. Challenges and Future Directions

In 2001, Baijiu industry experts Yuan Jian-cheng and Jiang Ting-hua proposed the concept of “pure Baijiu”, aiming to eliminate harmful impurities while preserving flavor [55]. Exogenous impurities continue to pose significant challenges to the safety and quality of Baijiu. These issues are compounded by gaps in monitoring capacity, regulatory standards, health-related research, and sustainable practices, particularly among small and medium-sized Baijiu brewers. Below, we summarize the major challenges and propose future research directions and industrial strategies that could help establish a framework for “pure Baijiu” with assured safety, quality, and market competitiveness.

3.1. Current Challenges in Monitoring Exogenous Impurities

Monitoring ultra-trace levels of exogenous impurities remains one of the most persistent obstacles in Baijiu safety control. Advanced detection methods such as ICP-MS and LC-MS/MS require costly equipment and expertise, leaving small and medium-sized Baijiu brewers unable to conduct routine screening.

Regulatory inconsistencies further complicate the picture. For example, the Chinese GB2763-2021 sets pesticide MRLs in grains, but no MRLs are established for Baijiu. GB 2762-2022 specifies maximum residue limits for heavy metals in Baijiu with a strict limit for lead at 0.5 mg/kg, yet currently, there are no specific regulatory limits established for other heavy metals in Baijiu. Brewers rely on raw material standards, underestimating process-related risks in finished product.

Additionally, growing consumer demand for low- and zero-alcohol Baijiu poses a new challenge. Market trends show increasing interest in lower alcohol options, with low- and zero-alcohol Baijiu products already available in the retail market [56,57]. De-alcoholization processes, such as vacuum distillation or reverse osmosis, are used to reduce alcohol content while preserving flavor, but their impact on exogenous impurities remains unclear due to limited research [7,58]. These de-alcoholization methods may concentrate non-volatile contaminants like heavy metals and mycotoxins as alcohol is removed, potentially increasing health risks in the final product. Without dedicated studies on impurity behavior during de-alcoholization and tailored detection methods or regulatory limits for these variants, ensuring safety becomes increasingly complex.

3.2. Future Directions for Safety Control

Since most exogenous risk components are introduced during production or storage, prevention remains the primary strategy, supplemented by active adsorption materials such as activated carbon for targeted removal. Small and medium-sized Baijiu brewers should adopt affordable best practices including sourcing certified low-pesticide grains and using food-grade plastic alternatives to prevent phthalate migration.

Moreover, regulatory updates are essential. By integrating Baijiu’s unique production characteristics (such as long-term storage) with scientific risk assessment principles, future standards should establish science-based, industry-tailored safety thresholds for exogenous impurities. This approach must account for the complex migration, transformation, and elimination pathways of impurities across the entire production chain, from raw grain to aged Baijiu. Such standards should be harmonized with Codex Alimentarius and EU regulations to enable seamless international trade and ensure global market access, particularly for emerging low- and zero-alcohol Baijiu variants, which face distinct safety profiles due to post-distillation processing. This alignment will not only elevate domestic safety governance but also position Baijiu as a globally competitive alcoholic beverage.

Technological innovation also offers significant promise. Future efforts should prioritize precision analytics and proactive safety control through affordable, scalable interventions tailored for small and medium-sized brewers. Low-cost, rapid detection tools, such as test strips for pesticide screening and portable electrodes for heavy metal detection, can be deployed on-site with minimal training, enabling routine monitoring without expensive instrumentation [59,60]. AI-powered smartphone apps integrated with simple spectrometers can provide real-time impurity alerts, democratizing quality control [61]. Beyond rapid on-site screening, AI systems can integrate multi-source data from fermentation, storage, and packaging to identify hidden risk patterns, optimize prevention strategies, and provide predictive warnings, enabling small and medium-sized brewers to achieve continuous and proactive safety control.

4. Conclusions

The pursuit of “pure Baijiu” represents an important direction for the modernization of the Baijiu industry. Over the past two decades, this vision has inspired continuous efforts by brewers such as Kongfuyan to improve production quality and safety [55]. When the concept was first proposed in 2001, harmful impurities mainly referred to endogenous hazardous substances such as methanol and fusel alcohols, which could be reduced through optimization of fermentation and distillation processes. With advances in science and public awareness, the definition of harmful impurities has broadened to include exogenous contaminants, such as plasticizers, which have only recently been recognized as safety risks.

Today, impurity control in larger Baijiu brewers is generally well managed, whereas such controls are generally lacking in smaller brewers. Yet these products account for the majority of Baijiu consumption, making impurity control in this sector essential for public health and industry reputation.

Small and medium-sized brewers often lack the resources for effective control, and current regulations still do not fully address Baijiu-specific safety concerns. Precision analytics, preventive measures, and science-based standards represent the most practical path forward. Affordable analytical tools, AI-assisted monitoring, and low-cost interventions can empower smaller brewers to improve safety management. By integrating the entire Baijiu production chain into risk evaluation, future standards should establish realistic, industry-tailored safety thresholds that align with international benchmarks. Collectively, these efforts will support the reduction of impurities in Baijiu while ensuring safety, authenticity, and market relevance.