Sustainable Strategies for Wine Colloidal Stability: Innovations in Potassium Bitartrate Crystallization Control

Abstract

Potassium bitartrate (KHT) crystallization, as the dominant factor compromising wine colloidal stability, necessitates advanced control strategies beyond conventional thermodynamic approaches. The formation of tartrate crystals is influenced by various factors, including temperature, pH, and the concentration of tartrate salts. Traditional methods of tartrate stabilization, such as cold stabilization and ion-exchange resins, while effective, are associated with high energy consumption and significant environmental impact. In recent years, with the growing emphasis on green and sustainable development, researchers have begun exploring more environmentally friendly innovative technologies. This review examines the factors affecting tartrate crystallization and their implications for wine quality, detailing traditional stabilization techniques as well as newer methods involving protective colloids and stabilizers. Special attention is given to recent advancements in green technologies, such as plasma surface modification, the use of zeolites as wine processing aids, and the synergistic application of algal polysaccharides. Finally, the paper outlines future directions for tartrate stabilization technology, underscoring the importance of green and sustainable practices in the wine industry.

1. Introduction

The crystallization of potassium hydrogen tartrate (KHT), colloquially referred to as “wine diamonds”, presents an ongoing challenge to the colloidal stability of wine [1]. Despite being chemically harmless, these crystalline deposits often provoke consumer skepticism due to their visible precipitation during storage. This perceptual contradiction highlights a fundamental tension within enology: while tartaric acid serves as an indispensable natural acidity regulator, its propensity to promote crystal nucleation complicates its management during winemaking [2,3]. As the primary organic acid in Vitis vinifera, tartaric acid occurs in sufficient concentrations (4–12 g/L) during fermentation to establish a metastable supersaturated state, inherently predisposing wine to the formation of KHT crystals [4].

The presence of KHT crystals embodies a dual paradox in modern winemaking; they are simultaneously celebrated as a hallmark of artisanal craftsmanship and criticized as a commercial liability. From a traditional perspective, these crystalline forms are regarded as indicators of minimal processing and authentic terroir expression, with premium producers often leveraging this perception to emphasize the purity of their practices and grape varieties. Although inert in terms of sensory impact and chemically inconsequential to wine composition, visible KHT deposits are frequently misinterpreted by consumers as a quality defect. Market surveys indicate that 40% of buyers associate these crystals with contamination or production flaws and are unlikely to repurchase wines that exhibit such sediments [5]. Addressing this misunderstanding necessitates costly stabilization measures to prevent post-bottling crystallization. Conventional stabilization strategies, such as cold stabilization and ion exchange, primarily aim to reduce ionic strength to minimize crystallization risk [6]. However, these methods are energy-intensive, may adversely affect wine quality, and often conflict with sustainability principles.

Given these challenges, developing sustainable and energy-efficient stabilization methods has become a key focus in modern enology. As illustrated in Figure 1, this review systematically explores the factors influencing tartaric acid crystallization in wine and its implications for wine quality, providing a detailed discussion of traditional stabilization techniques as well as emerging methods involving protective colloids and stabilizers. Recent advancements include plasma surface modification technology, which introduces amino, carboxyl, hydroxyl, or oxazoline functional groups to significantly enhance selective adsorption and regulation of specific wine components, such as proteins and tartrates, while being both environmentally friendly and efficient [7]. Zeolite-based technologies, leveraging their cation exchange and molecular adsorption properties, or in combination with steam-activated bentonite and natural minerals rich in chasozite and phillipsite, have proven to effectively lower K⁺ concentrations in wine, thereby inhibiting KHT crystallization [8]. Furthermore, these methods are considered sustainable due to their recyclability and low energy consumption. In addition, algal polysaccharide technologies reduce calcium tartrate (CaT) supersaturation by binding with Ca²⁺, thereby enhancing tartaric acid stability [9]. With natural origins and environmentally friendly characteristics, these approaches exhibit substantial potential for green and sustainable winemaking practices.

2. Formation Mechanism and Influencing Factors of Potassium Bitartrate Crystallization

2.1. Thermodynamic and Kinetic Fundamentals

The crystallization of KHT in wine originates from the dynamic equilibrium between dissolution and precipitation processes [2,8]. As illustrated in Figure 2, tartaric acid undergoes pH-dependent dissociation in aqueous ethanol solutions, forming bitartrate anions (HT⁻) that combine with K⁺ to create KHT complexes [10]. When environmental parameters alter during wine storage, particularly temperature fluctuations and ethanol concentration changes, this equilibrium shifts toward crystalline phase formation once supersaturation thresholds are exceeded [4].

Thermodynamically, KHT solubility decreases nonlinearly with temperature reduction and ethanol content elevation, establishing metastable conditions that persist until nucleation triggers phase transition [11]. Kinetically, the crystallization process progresses through three sequential regimes: initial heterogeneous nucleation at interfacial boundaries (e.g., container surfaces or colloidal particles), followed by anisotropic crystal growth along preferential crystallographic axes, and ultimately Ostwald ripening-mediated crystal maturation [3,12].

The delayed manifestation of visible crystals during bottle aging can be attributed to the inefficiency of homogeneous nucleation at moderate supersaturation levels, which requires a high degree of metastability to initiate. Heterogeneous nucleation, on the other hand, becomes the dominant mechanism once nucleation cores are formed, facilitating crystallization at lower supersaturation levels. The high viscosity of the wine matrix, combined with polyphenol–protein interactions, restricts molecular diffusion and aggregation rates, thereby influencing nucleation and further contributing to the delay in crystallization. While these factors slow the onset of visible crystals, the precise interplay between homogeneous and heterogeneous nucleation mechanisms remains complex. A detailed quantitative model would be necessary to fully describe and predict these processes, which should be a focus of future research efforts.

2.2. Influencing Factors

2.2.1. Temperature

The stability of KHT is influenced by temperature in a dual manner. The crystallization kinetics of KHT exhibit a pronounced temperature dependency, governed by two interrelated mechanisms. As the temperature decreases, the intrinsic reduction in KHT solubility establishes the thermodynamic driving force for crystallization, while simultaneously slowing molecular diffusion rates, thereby creating a kinetic barrier [13]. Consequently, low temperatures induce the formation of potassium hydrogen tartrate crystals. This dual effect explains the industrial practice of controlling cold stabilization; prolonged exposure at temperatures below 4 °C facilitates gradual crystal growth by maintaining sustained supersaturation, while mitigating the risk of rapid, uncontrolled nucleation. However, temperature has minimal impact on the precipitation rate of CaT; thus, cold stabilization is ineffective for CaT crystals [9]. In contrast, high temperatures promote crystal dissolution by enhancing ionic mobility, but prolonged exposure to elevated temperatures may facilitate certain chemical reactions, limiting practical applications due to the risk of sensory degradation.

2.2.2. Ionic Composition (K⁺/Ca²⁺)

The ionic milieu of wine directly governs crystallization pathways through competitive complexation equilibria. K⁺ preferentially bind HT⁻ under typical wine pH conditions, forming KHT crystals when concentrations exceed solubility thresholds [14]. Calcium ions, while less abundant, compete for tartrate species (T²⁻) at higher pH values, potentially inducing mixed crystal phases. The relative abundance of these cations creates a delicate balance; excess potassium drives KHT supersaturation, whereas elevated calcium levels may trigger heterogeneous crystallization through alternative salt formation.

2.2.3. Ethanol Content

Ethanol serves as a solvent modifier that significantly influences tartrate stability by modulating the dielectric constant. The reduced polarity of ethanol–water mixtures compared to pure water decreases ionic solvation capacity, effectively lowering tartrate solubility [15]. This dielectric exclusion effect becomes progressively pronounced with increasing alcohol content, necessitating adjusted stabilization protocols for high-alcohol wines where traditional cold stabilization may prove insufficient.

2.2.4. pH Value

As illustrated in Figure 3, the effect of pH on tartaric acid crystallization primarily lies in its regulation of the distribution of different forms of tartaric acid (H₂T, HT⁻, T²⁻), thereby influencing crystallization tendencies and the resulting crystallization products. In wine, tartaric acid mainly exists in the form of HT⁻, with K⁺ concentrations ranging from approximately 700 to 1600 mg/L and Ca²⁺ concentrations around 80 mg/L. Under strongly acidic conditions (pH < 3.0), protonation suppresses the formation of HT⁻, thereby limiting the complexation of KHT. When the pH is between 3.0 and 4.0, the availability of HT⁻ reaches its maximum, creating optimal conditions for KHT crystallization [13,16]. At pH levels exceeding 4.0, deprotonation generates T²⁻ which preferentially interact with calcium ions, leading to a crystallization tendency toward calcium tartrate phases [3]. This pH-dependent behavior underscores the importance of precise acidity control during stabilization processes.

2.2.5. Temporal Evolution

Extended bottle aging introduces progressive changes in wine colloidal structure that modulate crystallization kinetics. Oxidative polymerization of phenolic compounds generates supramolecular templates capable of lowering nucleation activation energies. Concurrently, evolving protein–polyphenol aggregates alter interfacial energies at potential nucleation sites [17,18]. These time-dependent transformations explain the phenomenon of delayed crystallization, where visible crystal formation often occurs months after bottling despite initial thermodynamic instability.

3. State of the Art for Controlling Tartrate Crystallization

3.1. Physical Stabilization Methods

Contemporary stabilization strategies employ multifaceted approaches to modulate tartrate equilibrium while preserving wine integrity, balancing technical efficacy with sensory preservation. As shown in Table 1, the main similarities and differences of several tartaric crystallization control methods are listed.

3.1.1. Cold Stabilization

As the industry benchmark, this method induces controlled KHT crystallization through sustained subzero temperatures (−4 °C to −8 °C). Research has shown that exposing Riesling dry white wine to cold treatment at −5.3 °C for 10–15 days significantly decreases tartaric acid concentration while improving tartaric stability by reducing pH levels [19,20]. While operationally straightforward, it faces critical limitations: extended treatment durations (2–3 weeks for red wines vs. 7–12 days for whites/rosés) incur substantial energy demands, and prolonged cryogenic exposure risks oxidative degradation of aromatic compounds, which is particularly problematic for color-sensitive red varieties [15]. Comparative analyses reveal differential matrix impacts: white/rosé wines may develop enhanced fruity characteristics through ester profile modifications, whereas red wines suffer negligible aromatic alterations at the cost of chromatic stability.

3.1.2. Ion Exchange Technology

This technique directly targets ionic equilibrium through cation-selective resins that replace K⁺/Ca²⁺ with H⁺ or Na⁺. Studies have shown that blending the wine sample with approximately 20% (v/v) of wine treated with cation-exchange resin effectively eliminates any detectable signs of tartaric instability [21]. Modern advancements have focused on optimizing resin formulations (strong-acid vs. weak-acid types) and operational parameters (e.g., flow rate and temperature), often in combination with electrodialysis, to effectively mitigate the risks of sodium retention. The process induces subtle pH reductions (0.07–0.12 units) and shifts in oxidation potential, necessitating careful monitoring, while having minimal impact on phenolic and aromatic profiles [16]. Its application in sparkling wine production demonstrates effective acidity enhancement, though over-treatment risks disrupting acid balance, which is a critical consideration for terroir expression [22,23].

3.1.3. Membrane Filtration

Emerging as an energy-efficient alternative, membrane technologies achieve molecular-level stabilization through crystal nuclei removal or nucleation site reduction. Advanced configurations like electrodialysis offer dual tartrate stabilization and acidity adjustment capabilities. Commercial applications demonstrate that 0.45 μm filtration effectively reduces turbidity while maintaining tannin and color stability, though it results in partial loss of acetylated anthocyanins [3]. Long-term aging studies indicate persistent particle size control in filtered wines, with sensory profiles showing filtration-level-dependent aroma variations but consistent texture preservation [24]. Compared to traditional clarification methods, membrane processes provide superior environmental compatibility and flavor stability, positioning them as sustainable solutions for modern winemaking.

3.1.4. Electrodialysis

Electrodialysis (ED) achieves efficient ion separation by applying an electric field to drive ions through selective membranes. The core mechanism involves the targeted removal of metal cations (e.g., Ca²⁺) and tartrate ions from wine, effectively preventing crystal precipitation through a dual-action approach [3,6]. By eliminating the need for traditional chemical additives, ED minimizes contamination risks and aligns with consumer preferences for additive-free products [11]. ED offers a compact and automated operation while enabling byproduct valorization through the recovery of valuable compounds such as tartaric acid (9.9 g/L) and potassium hydroxide (5.6 g/L) [25]. To address fouling in aliphatic membranes (CJMA-6/CJMC-5), researchers have developed an innovative in situ cleaning strategy that combines a KCl hydroalcoholic solution with electric field polarity reversal. This method effectively disrupts colloidal layers, selectively recovers polyphenols, and inhibits biofouling by blocking microbial nutrient pathways. However, the cleaning and replacement of membranes have increased the overall cost of ED processes in the food industry by more than 40% [26]. By leveraging the π-π stacking-resistant properties of aliphatic membranes, a sustainable closed-loop system has been established, integrating fouling control with resource recovery [25]. Evolving from a stabilization technique into a cornerstone of the circular economy in winemaking, ED’s integration with advanced membrane materials and intelligent control systems is poised to drive the industry towards a low-carbon, resource-efficient transformation.

3.2. Chemical Stabilization Approaches

Modern enology is increasingly embracing additive-based strategies to achieve tartrate stability while adhering to organic winemaking principles. Compared to traditional methods, protective colloid technology combines environmental benefits—such as lower energy consumption and reduced chemical intervention—with economic advantages, including streamlined operations and cost efficiency. This approach is particularly well-suited for sustainable red wine production.

3.2.1. Metatartaric Acid

Metatartaric acid is a significant oenological stabilizer authorized by the International Organisation of Vine and Wine (OIV) for tartaric stabilization in wines, with a maximum permitted dosage of 100 mg/L [27]. Its mechanism of action involves protective colloid stabilization, where it adsorbs onto the surface of tartrate crystals to inhibit KHT precipitation by interfering with crystal growth [28]. In contrast to conventional cold stabilization, which removes excess ions through low-temperature-induced crystallization, metatartaric acid eliminates the potential drawbacks associated with cold treatment. These include alterations in volatile composition—such as increased ester levels and reduced higher alcohols in white and rosé wines—and color deterioration, including reduced color intensity in rosé wines and a loss of monomeric anthocyanins in red wines. However, the following limitations exist: as a semi-synthetic additive, its stabilizing efficacy degrades over time, and when combined with mannoproteins, it significantly reduces red wine filterability (FI > 500), though it does not affect white or rosé wines [29,30]. Despite these technical constraints, the European Food Safety Authority (EFSA) confirms no safety concerns for its use as a food additive under current regulations [31], providing scientific support for its application in winemaking.

3.2.2. Carboxymethyl Cellulose (CMC)

Carboxymethyl cellulose (CMC), a plant-derived polymer, is synthesized through a two-step process: alkali treatment of wood cellulose to form an alkali-cellulose complex, followed by etherification with monochloroacetic acid [32]. Its low production cost, reduced energy consumption, and ease of application align with low-carbon process requirements [33]. Approved by OIV since 2009 with a current maximum dosage of 200 mg/L for white/rosé wines, CMC stabilizes through multifaceted mechanisms. Its anionic polysaccharide structure enables electrostatic interactions with KHT crystals and metal ions (K⁺/Ca²⁺), effectively inhibiting nucleation and altering crystal morphology. The degree of substitution (DS) critically determines efficacy by modulating cation-binding capacity. Studies have demonstrated that while CMC induces modest increases in color intensity and turbidity in red wines [32], it does not trigger precipitation and preserves total phenol retention rates above 95%, thereby challenging prior limitations regarding its applicability in red winemaking. Furthermore, CMC-treated wines-maintained CaT throughout a one-year storage period, with no significant effects observed on phenolic profiles, color evolution, or overall astringency intensity [34,35]. Comparative studies highlight CMC as a superior alternative to cold stabilization for preserving volatile aromas, although protein-induced haze continues to pose a challenge in certain matrices.

3.2.3. Mannoproteins

Mannoproteins exhibit multifunctional roles in wine, including enhancing aromatic profiles, stabilizing pigments, reducing astringency, and preventing protein haze and potassium bitartrate crystallization [36]. Derived from yeast cell walls, these glycoproteins combine mannose polymers with protein backbones to create crystal growth inhibitors. Their mechanism involves preferential adsorption onto nascent crystal nuclei through protein–crystal surface interactions [37]. In white wines, mannoproteins enhance tartrate stability as evidenced by reduced conductivity drop, while their impact on red wines proves negligible due to inherent colloidal complexity. While mannoproteins optimize wine stability through their natural and multifunctional properties, their application requires integration with traditional techniques and incurs higher costs. Nevertheless, their role in reducing environmental impact and promoting resource recycling positions them as a pivotal direction for sustainable winemaking.

3.2.4. Potassium Polyaspartate (KPA)

Potassium polyaspartate (KPA) and its sodium salt (PASP) demonstrate notable efficacy in inhibiting KHT precipitation. Early studies by Bosso et al. revealed that polyaspartates (PAs) with varying salt forms (Na/K) and molecular weights (2–8 kDa), when dosed at 100 mg/L, effectively stabilized wines with superior and longer-lasting performance compared to traditional metatartaric acid (MTA) [38]. Subsequent research confirmed KPA’s applicability: cold tests showed 100 mg/L and ensured stability for one year, while excessive doses (1000 mg/L) increased turbidity. Unlike MTA, KPA did not alter filterability (0.45 μm) or color browning protection in white wines, nor exhibited chelating effects on Fe/Cu ions or significant impacts on oxidative processes (e.g., SO₂, acetaldehyde, color). Under elevated temperatures (40 °C for 45 days), KPA maintained stabilization efficacy [18]. Compared to traditional stabilizers, polyaspartates offer high efficiency, thermal resilience, and minimal interference with wine composition, though high-dose turbidity effects require cautious control.

Table 1. Comparison diagram of tartaric acid crystallization control methods.

Method	Principle	Sustainability	Cost and Resource Requirements	Impact on Wine Quality	Regulatory Requirements	Application Scenarios	Efficacy
Cold stabilization	Induction of potassium bitartrate (KHT) precipitation at low temperatures, followed by filtration	High energy consumption, less environmentally sustainable	Require cooling equipment, high operational costs	Prolonged low-temperature exposure affects red wine color; slight reduction in aromatic compounds, but minimal impact	Comply with global regulations	Suitable for large-scale production, particularly for white and sparkling wines	Effective, but requires long processing time
Electrodialysis	Application of an electric field to remove tartrate ions via membrane separation	Low energy consumption, relatively eco-friendly; membranes are prone to biofouling	High initial equipment investment; low long-term operational costs	Minimal impact on volatile aromatic compounds	Comply with international regulations	Suitable for large-scale production of all wine types	Highly precise, achieves stability in a short time
Ion exchange	Replacement of tartrate ions with other ions using ion-exchange resins	Low energy consumption; resin replacement generates waste, reducing sustainability	High costs for resins and equipment	Limited impact on flavor; excessive treatment can disrupt acid balance and alter taste	Some countries impose restrictions; regulatory confirmation is required	Medium to large-scale production, primarily for white wines	Effective; rapidly removes tartrates
Membrane filtration	Retention of tartrate crystals using membranes with specific pore sizes (≤0.45 µm)	Moderate sustainability; concerns over water consumption and membrane disposal	High initial cost; moderate operational costs	Preserves flavor; excessive filtration may remove some flavor compounds	Comply with food-grade filtration standards	Large-scale production, especially for white and sparkling wines	Effective, short processing time
Metatartaric acid	Addition of metatartaric acid to form complexes with tartrates, preventing crystal growth	Chemical additive use reduces environmental sustainability	Low cost, simple operation	Minimal flavor impact, may cause subtle taste changes	Permitted in many countries, but subject to dosage restrictions	Small-scale production, particularly for white wines	Effective in the short term; long-term stability is limited, especially in red wines
Carboxymethyl cellulose	Adsorption onto the surface of KHT crystals to inhibit crystal growth	Biodegradable and relatively eco-friendly	Moderate cost, simple addition process	Minimal impact on flavor; may cause slight turbidity in certain conditions	Comply with EU regulations; permitted in some countries	Medium-to-small-scale production, especially for white and light red wines	Significant effect; stability may be reduced under extreme conditions
Mannoprotein	Natural polymers derived from yeast inhibit crystal growth by adsorbing onto nascent nuclei	Derived from natural sources; environmentally sustainable	High cost; suitable for organic and premium wine production	Enhances aromatic properties; stabilizes color; reduces astringency	Permitted in many countries; subject to dosage regulations	High-end wine production, especially white and light red wines	Excellent effect, provides long-term tartrate stability
Potassium polyaspartate	Compete with tartrates for binding calcium and potassium ions, inhibiting crystal growth	Biodegradable, though classified as a chemical additive	Low cost; simple and efficient application	Minimal effects on wine components; no significant impact on white and rosé wines; may affect filterability of red wines	Regulatory approval required in certain countries	Small-scale production, primarily for white wines	Highly effective; ensures long-term stability with proper dosage control

Table 1. Comparison diagram of tartaric acid crystallization control methods.

Method	Principle	Sustainability	Cost and Resource Requirements	Impact on Wine Quality	Regulatory Requirements	Application Scenarios	Efficacy
Cold stabilization	Induction of potassium bitartrate (KHT) precipitation at low temperatures, followed by filtration	High energy consumption, less environmentally sustainable	Require cooling equipment, high operational costs	Prolonged low-temperature exposure affects red wine color; slight reduction in aromatic compounds, but minimal impact	Comply with global regulations	Suitable for large-scale production, particularly for white and sparkling wines	Effective, but requires long processing time
Electrodialysis	Application of an electric field to remove tartrate ions via membrane separation	Low energy consumption, relatively eco-friendly; membranes are prone to biofouling	High initial equipment investment; low long-term operational costs	Minimal impact on volatile aromatic compounds	Comply with international regulations	Suitable for large-scale production of all wine types	Highly precise, achieves stability in a short time
Ion exchange	Replacement of tartrate ions with other ions using ion-exchange resins	Low energy consumption; resin replacement generates waste, reducing sustainability	High costs for resins and equipment	Limited impact on flavor; excessive treatment can disrupt acid balance and alter taste	Some countries impose restrictions; regulatory confirmation is required	Medium to large-scale production, primarily for white wines	Effective; rapidly removes tartrates
Membrane filtration	Retention of tartrate crystals using membranes with specific pore sizes (≤0.45 µm)	Moderate sustainability; concerns over water consumption and membrane disposal	High initial cost; moderate operational costs	Preserves flavor; excessive filtration may remove some flavor compounds	Comply with food-grade filtration standards	Large-scale production, especially for white and sparkling wines	Effective, short processing time
Metatartaric acid	Addition of metatartaric acid to form complexes with tartrates, preventing crystal growth	Chemical additive use reduces environmental sustainability	Low cost, simple operation	Minimal flavor impact, may cause subtle taste changes	Permitted in many countries, but subject to dosage restrictions	Small-scale production, particularly for white wines	Effective in the short term; long-term stability is limited, especially in red wines
Carboxymethyl cellulose	Adsorption onto the surface of KHT crystals to inhibit crystal growth	Biodegradable and relatively eco-friendly	Moderate cost, simple addition process	Minimal impact on flavor; may cause slight turbidity in certain conditions	Comply with EU regulations; permitted in some countries	Medium-to-small-scale production, especially for white and light red wines	Significant effect; stability may be reduced under extreme conditions
Mannoprotein	Natural polymers derived from yeast inhibit crystal growth by adsorbing onto nascent nuclei	Derived from natural sources; environmentally sustainable	High cost; suitable for organic and premium wine production	Enhances aromatic properties; stabilizes color; reduces astringency	Permitted in many countries; subject to dosage regulations	High-end wine production, especially white and light red wines	Excellent effect, provides long-term tartrate stability
Potassium polyaspartate	Compete with tartrates for binding calcium and potassium ions, inhibiting crystal growth	Biodegradable, though classified as a chemical additive	Low cost; simple and efficient application	Minimal effects on wine components; no significant impact on white and rosé wines; may affect filterability of red wines	Regulatory approval required in certain countries	Small-scale production, primarily for white wines	Highly effective; ensures long-term stability with proper dosage control

3.3. Other Methods

3.3.1. Fermentation Process Optimization

Precise temperature modulation during fermentation critically regulates tartaric acid solubility dynamics, maintaining the dissolution–crystallization equilibrium to prevent excessive precipitation [39]. While low temperatures (<10 °C) promote crystallization through reduced solubility, elevated temperatures (>20 °C) enhance ionic mobility and dissolution capacity. Strategic thermal management enables customized stabilization; white wines achieve stable supersaturation (14.8 °C saturation temperature post-treatment), even at 0 °C, whereas red wines inherently stabilize at lower thresholds (9.2 °C saturation temperature) due to their complex colloidal matrix [40]. This differential thermal behavior necessitates varietal-specific protocols to balance stability and quality preservation.

3.3.2. Storage Condition Strategy

Post-fermentation storage temperature selection must account for wine type-specific crystallization thresholds. Prolonged low-temperature exposure (<15 °C) risks destabilization through progressive KHT nucleation, particularly detrimental to white wines requiring higher stabilization temperatures [41,42]. Red wines demonstrate relative stability under moderate cooling (12–16 °C) but remain susceptible to delayed crystallization during extended cold storage [42]. The operational paradigm emphasizes avoiding sustained suboptimal temperatures rather than absolute temperature limits, leveraging wine’s inherent stabilization potential through controlled environmental management.

4. Recent Advances in Green and Sustainable Strategies for Controlling Tartrate Crystallization

4.1. Plasma Surface Modification Technology

Plasma surface modification technology, as a green and sustainable innovation, enhances the selective adsorption properties of materials through chemical functional modification, enabling efficient removal or regulation of wine components. This method complements and replaces traditional techniques, offering advantages in efficiency, environmental friendliness, and resource sustainability. By introducing specific chemical functional groups (e.g., amino, carboxyl, hydroxyl, or oxazoline groups) onto substrate surfaces [43], plasma technology significantly improves the selective adsorption capacity for target components in wine. Research has confirmed that surfaces with amino and carboxyl groups exhibit strong adsorption for white wine, hydroxyl surfaces preferentially adsorb rosé wine, and acrylic acid surfaces show the strongest adsorption for red wine [44].

In the removal of haze-causing proteins that lead to thermal instability, plasma-functionalized magnetic nanoparticles demonstrate exceptional performance. Studies indicate that acrylic acid-modified nanoparticles can efficiently capture pathogenesis-related proteins in wine while preserving the integrity of phenolic compounds, thus avoiding any compromise to the wine’s flavor profile [7]. Furthermore, carboxyl-modified surfaces outperform oxazoline and amino-modified surfaces in protein capture efficiency [45], highlighting the potential of functionalized surfaces in regulating protein adsorption and removal.

Plasma modification technology also shows significant advantages in the cold stabilization of white wine. By constructing coatings of acrylic acid (AA), allylamine (AcrA), and oxazoline (POx) on substrate surfaces, research has demonstrated that surface chemistry can directionally regulate the binding mechanisms of KHT at a mild temperature of 15 °C. The binding efficiency in cold/heat unstable wines follows the order AA > POx > AcrA, while the protein-stabilized system exhibits an inverse binding trend [42]. This technology not only effectively reduces potassium and tartaric acid concentrations (with an average reduction of 22% in K⁺ and 23% in tartaric acid) but also maintains the stability of key phenolic compounds, preserving the sensory characteristics of the wine. Additionally, the recyclability of the coating materials aligns with circular economic principles, making it particularly suitable for industrial applications in large-scale wineries.

4.2. Zeolites as Wine Processing Adjuvants

In recent years, the wine industry has increasingly emphasized green and sustainable development. The limitations of traditional stabilization techniques, such as high energy consumption, significant waste generation, and low environmental sustainability, have driven the emergence of innovative technologies. Zeolites, whether natural or synthetic aluminosilicate minerals, have gained significant attention for tartrate stabilization thanks to their unique microporous structure, high cation exchange capacity, and excellent adsorption properties [46]. Zeolites offer environmental advantages, including energy efficiency, process simplification, recyclability, and reduced use of chemical additives [47].

Research on zeolites in winemaking has primarily focused on their dual potential for tartrate stabilization and protein removal, while mitigating the drawbacks of conventional methods. Zeolites selectively reduce K⁺ concentrations in wine through cation exchange and molecular adsorption, effectively inhibiting the formation of KHT crystals. This mechanism significantly reduces energy consumption and waste emissions during wine production. To enhance protein and tartrate stability, researchers have combined zeolites with bentonite. Mercurio et al. [8] proposed an innovative approach: steam-activated bentonite was used to enhance protein adsorption, while natural minerals rich in chabazite and phillipsite were employed to synergistically reduce K⁺ concentrations. In simulated wine solutions, this method reduced potassium ion levels by approximately 50%, significantly improving stability. Additionally, the composite material can be regenerated and repurposed as an agricultural soil amendment, minimizing environmental waste.

To overcome the limitations of sequential treatments, multifunctional zeolite-based processing aids have been developed, enabling simultaneous achievement of protein thermal stability and tartrate cold stability in white wines through a single application [47]. For instance, Mierczynska-Vasilev et al. [45] found that treating wine with dry or hydrated natural zeolites reduced K⁺ concentrations by over 30% without affecting sensory quality. Tim Reilly et al. [47] further optimized performance by calcining zeolites, enhancing their adsorption and ion exchange capabilities, which significantly reduced tartrate and protein levels within 3 h while controlling calcium ion concentrations. Compared to bentonite, zeolite treatment improved wine recovery rates, and regenerated zeolites can be reused, providing a cost-effective solution for small and medium-sized wineries while reducing solid waste.

4.3. Synergistic Innovation of Algal Polysaccharides

The issue of tartaric stability in wine has become increasingly critical under global climate change. Traditional techniques such as electrodialysis and cation exchange resins face challenges including high costs, extended processing cycles, and secondary pollution risks, while chemical additives are constrained by hydrolysis-induced deactivation or precipitation risks [48]. In this context, algal-derived polysaccharides, such as alginic acid and carrageenan, have emerged as innovative green solutions, offering the benefits of their natural origin, OIV-certified clean label advantages, and multi-target stabilization mechanisms [27,36].

Alginic acid demonstrates dual functionality through electrostatic complexation and protein flocculation. Its strong electronegativity (zeta potential −49.3 mV) enables efficient Ca²⁺ binding, directly reducing CaT supersaturation and crystallization risks. Under low pH conditions, it flocculates positively-charged proteins via charge neutralization, preserving tannins while simplifying clarification processes [9,49]. Comparative studies show alginic acid outperforms CMC and KPA in mitigating CaT instability, with its calcium-alginate complexes being recyclable as functional materials, achieving resource circularity [9]. However, its sensory impact on wine remains unverified.

The iota-/kappa-blend carrageenan operates through a colloidal stabilization mechanism via ternary “carrageenan-Ca²⁺-protein” complexes. Research confirms its CaT stabilization arises from colloidal Ca²⁺ immobilization rather than ion removal, reducing CaT saturation temperature (T-sat CaT) by 6.7 °C on average. It synergizes with sodium bentonite through competitive protein adsorption, liberating additional binding sites while enhancing KHT stability [50]. This approach minimizes ionic intervention intensity, circumventing membrane fouling issues inherent to electrodialysis.

We conducted a comparative analysis of the above three green innovation methods, and the results are shown in

Table 2. Comparison diagram of three green innovative control methods for tartaric acid crystallization.

Green Innovation Method	Plasma Surface Modification Technology	Zeolite as a Wine Processing Adjuvant	Synergistic Innovation of Algal Polysaccharides
Technical Principle	Introduces specific chemical functional groups (e.g., amino, carboxyl, hydroxyl) on material surfaces via plasma technology to enhance selective adsorption capabilities	Utilizes the microporous structure and high cation exchange capacity of zeolite to reduce potassium ion concentration through ion exchange and molecular adsorption, inhibiting tartrate crystallization	Employs the electrostatic complexation and colloidal stabilization mechanisms of algal polysaccharides (e.g., alginate and carrageenan) to reduce the risk of tartrate crystallization
Main Applications	Removal and regulation of wine components, particularly protein and tartrate adsorption	Tartrate stabilization and protein removal, suitable for both cold and heat stabilization of wine	Tartrate stabilization, particularly for calcium tartrate (CaT) stability
Advantages	Strong selective adsorption capability; Efficient removal of proteins and tartrates; Recyclable materials, suitable for large-scale industrial applications	Reduces energy consumption and waste emissions; Can be combined with other materials (e.g., bentonite); Zeolite is renewable, suitable for small-to-medium-sized wineries	Natural origin, clean label; Multi-target stabilization mechanism; Reduces ionic interference, avoiding membrane fouling issues
Limitations	Technically complex, high equipment costs; Impact on wine sensory properties not fully validated	Adsorption efficiency of zeolite is limited by its structure and processing conditions; Requires combination with other materials for optimal results	Impact on wine sensory properties not fully validated; Complex stabilization mechanisms of polysaccharides may require further optimization
Environmental Friendliness	Efficient and eco-friendly, with recyclable coating materials, aligning with circular economy principles	High energy efficiency, reduced use of chemical additives, recyclable zeolite, and reduced solid waste	Natural origin, OIV-certified clean label, reduced use of chemical additives, and recyclable polysaccharide complexes
Research Progress	Demonstrated selective adsorption capabilities for various wine components, with excellent performance in low-temperature stabilization	Demonstrated dual potential of zeolite in tartrate stabilization and protein removal, with performance optimizable through calcination	Demonstrated potential of alginate and carrageenan in tartrate stabilization, though sensory impacts require further study

.

5. Future Research Perspectives

5.1. Construction of a Regulatory Model for Tartrate Crystallization

Classical nucleation theory (CNT) provides a foundational framework for studying nucleation processes; however, its applicability is limited, particularly in complex systems where it fails to fully capture the dynamics of nucleation. Non-classical nucleation pathways, such as two-step nucleation mechanisms, have been shown to play a critical role in systems like solution crystallization [51,52]. Nevertheless, the kinetic and thermodynamic processes underlying these pathways remain insufficiently understood and require further investigation.

The crystallization mechanism of KHT is governed by a combination of thermodynamic, kinetic, and intermolecular interactions. These factors collectively determine the crystallization rate and crystal morphology. While supersaturation serves as the primary driving force for crystallization, the inhibition of nucleation and crystal growth is crucial for effectively controlling KHT crystallization [4].

To date, no CNT-based model has been developed to regulate KHT crystallization. We propose that constructing such a model necessitates the integration of the following key factors: thermodynamic factors—supersaturation, interfacial free energy, and free energy barriers; kinetic factors—diffusion behavior, adsorption kinetics, and nucleation rate; non-classical nucleation pathways—pre-nucleation clusters and two-step nucleation mechanisms; and solution properties—temperature, pH, dielectric constant, and viscosity.

5.2. Green Technological Innovation

The sustainability imperative drives the development of energy-efficient physical interventions and biological solutions. Low-temperature plasma technology shows promise for simultaneous tartrate stabilization and microbial control, with ongoing optimization of gas composition and exposure parameters to minimize oxidative collateral effects. Synthetic biology breakthroughs enable CRISPR-engineered microbial strains capable of targeted tartaric acid metabolism, potentially revolutionizing stabilization through upstream acid reduction during fermentation [53,54,55]. While plasma treatment demonstrates immediate K⁺ removal efficacy, microbial engineering approaches require meticulous metabolic flux control to preserve essential acidity balance. Both technologies demand lifecycle assessments to validate environmental benefits against traditional methods. Contemporary stabilization strategies employ multifaceted approaches to modulate tartrate equilibrium while preserving wine integrity, balancing technical efficacy with sensory preservation.

5.3. Consumer-Centric Market Adaptation

Reconciling technical solutions with market realities necessitates systematic evaluation of crystallization’s sensory and perceptual impacts [56]. Advanced sensorics approaches integrate artificial sensory panels with electronic tongue/nose systems to quantify textural and aromatic modifications induced by stabilization treatments. Cross-cultural consumer studies employing neurophysiological metrics (e.g., eye-tracking, EEG) decode subconscious responses to crystal-containing wines, informing label design and marketing strategies. This consumer intelligence pipeline aims to establish evidence-based thresholds for “natural crystal” labeling while guiding regulatory framework updates to accommodate evolving quality paradigms.

6. Conclusions

The crystallization of potassium bitartrate, colloquially known as “wine diamonds”, represents a persistent challenge in enology, reflecting an inherent colloidal instability in wine. While chemically inert and organoleptically neutral, these crystalline deposits continue to pose significant marketability challenges by reinforcing consumer misperceptions of quality defects. This study systematically investigates the critical factors influencing tartrate crystallization and provides a comparative analysis of the advantages, limitations, and mechanisms of traditional stabilization techniques. Building upon this foundation, the research introduces innovative approaches grounded in green chemistry principles, marking a shift from traditional suppression-based methods to controlled crystallization strategies.

This study highlights the necessity of constructing a regulatory model for tartrate crystallization based on classical nucleation theory and emphasizes the importance of considering a comprehensive range of factors, including kinetics, thermodynamics, and solution properties. In addition, the research explores the sociocultural dimensions of wine stabilization, proposing a redefinition of tartrate crystallization as a natural hallmark of traditional winemaking rather than a defect. This approach aims to enhance consumer acceptance of innovative stabilization strategies. By integrating scientific communication with technological innovation, this framework not only preserves the cultural heritage of winemaking but also promotes market adaptation to sustainable practices.

In conclusion, this research redefines the paradigm of wine stabilization management, introducing a comprehensive framework of precision engineering, low-carbon production, and multidimensional value creation. The integration of smart biotools with green engineering principles transforms tartrate management from crystallization suppression to controlled crystallization, achieving a delicate balance among quality, sustainability, and cultural preservation. This framework not only provides a sustainable solution for the wine industry but also serves as a model for advancing circular agroindustrial development in a climate-resilient future. By synergizing ecological, economic, and cultural dimensions, this study offers critical insights into the broader transformation of traditional food industries.