The Iceberg Effect: Mastering Menthol Solubility Limits in High-VG E-Liquid Formulations

Author: R&D Team, CUIGUAI Flavoring

Published by: Guangdong Unique Flavor Co., Ltd.

Last Updated:  Feb 25, 2026

Introduction: The High-VG Trend and the Crystalline Challenge

The electronic liquid industry has witnessed a decisive shift toward high-Vegetable Glycerin (VG) formulations. Driven by consumer demand for denser vapor production and smoother throat hits, “Max VG” or 70/30 VG/PG ratios have become the industry standard for sub-ohm vaping devices. Simultaneously, menthol remains one of the most enduring and popular flavor profiles globally, prized for its cooling sensation and throat hit augmentation.

However, converging these two trends—high concentrations of menthol in high-VG bases—presents significant technical challenges for manufacturers. The most formidable of these is menthol crystallization, often referred to in production circles as “crashing out.”

A perfectly clear, homogenous e-liquid can turn into a cloudy suspension of shards or a solid icy mass if the solubility limits are exceeded or environmental conditions shift. This is not merely an aesthetic issue; it is a functional failure. Crystallized menthol clogs coils, alters flavor delivery, and ruins the consumer experience, leading to product returns and brand damage.

As a specialized manufacturer of fragrances and flavor compounds for e-liquids, we understand that stable formulations are the bedrock of a successful product line. This technical guide delves deep into the physical chemistry of menthol solubility. We will define the limits of high-VG bases, explore the thermodynamics of crystallization, and provide actionable strategies for formulators to ensure their menthol flavors remain stable, clear, and potent from the mixing vessel to the customer’s tank.

Menthol Crystallization in Laboratory Beakers

Section 1: The Chemistry of Cool – Understanding the Solute (Menthol)

To master solubility, we must first understand the solute. Menthol (C₁₀H₂₀O) is a cyclic terpene alcohol found naturally in peppermint and other mint oils, though much of the industry supply is now synthesized for purity and consistency.

At room temperature (around 20-25°C or 68-77°F), pure menthol exists as a crystalline solid. It is characterized by a waxy texture and a distinct, potent aroma. The critical physical property relevant to e-liquid formulation is its melting point, which typically ranges between 41°C to 44°C (106°F to 111°F), depending on the specific isomeric purity (L-menthol being the most common).

Because menthol’s natural state at room temperature is solid, it requires energy (heat) or a suitable solvent to transition into and remain in a liquid phase solution. In an e-liquid, the menthol molecules must be effectively “caged” or surrounded by solvent molecules to prevent them from re-associating with each other and reforming a solid crystal lattice structure.

The stability of this liquid state depends entirely on the compatibility between the solute (menthol) and the solvent (the PG/VG base).

Section 2: The Solvent Base – The War Between PG and VG

The fundamental cause of menthol crystallization in modern e-liquids is the inherent difference in solvent properties between Propylene Glycol (PG) and Vegetable Glycerin (VG). They are not interchangeable carriers when it comes to dissolving solids.

2.1 The Power of Propylene Glycol (PG)

PG (C₃H₈O₂) is a relatively thin, somewhat polar molecule. In the world of e-liquid chemistry, PG is the primary workhorse for flavor carrying.

• Polarity and Miscibility:PG has a polarity that allows it to interact reasonably well with a wide range of organic flavor compounds, including alcohols like menthol. The principle of “like dissolves like” applies here. PG molecules can effectively squeeze between menthol molecules, disrupting their crystalline structure and holding them in solution.
• Viscosity:PG has low viscosity, allowing for easier movement of molecules and faster dissolution rates.

A pure PG base can hold a surprisingly high concentration of menthol—some estimates suggest upwards of 40-50% by weight at standard room temperature before saturation is reached, though practical vaping applications rarely require this much.

2.2 The Challenge of Vegetable Glycerin (VG)

VG (C₃H₈O₃), also known as glycerol, is drastically different. It is a sugar alcohol that is significantly thicker and more viscous than PG.

• Hydrogen Bonding and Viscosity:According to data from the National Center for Biotechnology Information (NCBI), glycerol is characterized by extensive intermolecular hydrogen bonding that forms a complex, stable network within the liquid itself. This internal network results in its characteristic high viscosity.
• Poor Solvent Capacity for Non-Polar Solids:Because VG molecules are so strongly attracted to each other via hydrogen bonds, they are less willing to “make space” for bulky organic molecules like menthol. While VG is polar (due to its hydroxyl groups), its dense network makes it a poor solvent for dissolving large amounts of solid crystalline materials compared to PG.
• The takeaway is stark:PG wants to dissolve menthol; VG actively resists it. As the ratio of an e-liquid shifts in favor of VG, the total solvent capacity of the formulation drops precipitously.

Citation 1: National Center for Biotechnology Information. “PubChem Compound Summary for CID 753, Glycerol.” PubChem. Accessed [Current Date]. (Source for chemical structure and physical properties of Glycerol/VG).

Section 3: The Phenomenon of Crystallization (The “Crash”)

Understanding why menthol crashes is crucial to prevention. Crystallization in e-liquid is rarely an instantaneous event; it is usually the result of a system trying to return to equilibrium.

3.1 Saturation vs. Supersaturation

Every solvent system has a saturation limit at a specific temperature—the maximum amount of solute it can stably hold.

When manufacturers create high-menthol e-liquids, they often use heat during the mixing process. Heating the VG/PG base increases the kinetic energy of the solvent molecules, spreading them apart and allowing them to accept more menthol than they could at room temperature.

When the liquid cools back down to room temperature, it often becomes supersaturated. This is an unstable state where the liquid holds more dissolved menthol than is theoretically possible at that lower temperature. The system is under stress and desperate to eject the excess menthol to return to a stable saturation point.

3.2 Triggers for Crystallization

A supersaturated high-VG solution is like a loaded spring waiting to be released. Several factors can trigger the “crash”:

• Temperature Shock (The Winter Factor):This is the most common cause. As temperature drops, the solubility limit of the base decreases significantly. A formulation that is stable at 25°C in the lab may crash violently when shipped in a truck at 5°C during winter. The cold forces the menthol molecules out of solution.
• Nucleation (Seeding):Supersaturated solutions need a starting point to crystallize. This can be a microscopic piece of dust, a rough spot on the inside of a bottle, or, most commonly, an undissolved grain of menthol from an incomplete mixing process. Once a single “seed” crystal forms, it acts as a template, and surrounding menthol molecules rapidly attach to it, causing a chain reaction crash.
• Agitation:Sometimes, heavy vibration during transport can provide the necessary activation energy to knock a supersaturated solution out of its unstable state and initiate crystallization.

Molecular View: Menthol Dissolution vs. Crystallization

Section 4: Defining the Limits – Practical Solubility Data in High-VG

Formulators often ask for a hard number: “What is the maximum percentage of menthol I can put in 80% VG?”

Unfortunately, there is no single universal number because it depends heavily on the remaining 20% (is it PG? Flavor concentrates containing alcohol?), the exact temperature, and the storage time. However, based on extensive industry empirical testing and chemical principles, we can establish functional guidelines.

• Pure PG:Can comfortably hold 30%+ menthol at room temperature.
• 50/50 VG/PG:Generally stable up to roughly 15-20% menthol, depending on ambient temperature.
• 70/30 VG/PG (High VG Standard):The danger zone begins here. Stability is usually maintained up to roughly 8-12% menthol at standard room temperature (20°C). Below 10°C, this limit drops significantly.
• 80/20 VG/PG and higher (“Max VG”):The solubility limit plummets. At room temperature, a true 80%+ VG mix may struggle to stably hold more than 3-6% pure menthol crystals over long periods.

It is critical to realize that many commercial “Max VG” e-liquids that taste heavily of menthol are not using pure crystals directly in the final mix. They are using pre-dissolved menthol concentrates (usually PG-based) and stretching the definition of “Max VG,” or they are operating right at the edge of supersaturation and hoping the product is consumed before it crashes.

Research into the thermodynamics of solubility in mixed solvents confirms that the solubility of a hydrophobic solute (like menthol) decreases non-linearly as the fraction of water or hydrophilic co-solvents (like glycerol) increases.

Citation 2: Jouyban, A. (2008). Review of the dielectric related models for prediction of drug solubility in mixed solvents. Pharmazie, 63(2), 83-92. (This citation provides scientific context on how mixed solvent systems affect solubility characteristics).

Section 5: Master Formulation – Strategies to Prevent Crystallization

As a manufacturer of fragrance and flavor compounds, we assist clients in navigating these limitations. If your target flavor profile requires high menthol impact in a high-VG base, simple mixing will not suffice. You must employ specific formulation and processing strategies.

Strategy 1: The PG Pre-Dissolve (The Golden Rule)

Never attempt to dissolve solid menthol crystals directly into cold Vegetable Glycerin. It will result in immediate failure or incredibly long processing times with a high risk of future crashing.

Menthol crystals must always be pre-dissolved in the PG portion of your formulation (or flavor concentrates) first.

• Calculate the total PG content available in your recipe (including PG from other flavorings).
• Add the menthol crystals to this PG fraction.
• Apply gentle heat (40-50°C) and stir until the solution is completely clear and no solid crystals remain.
• Only once the menthol is fully integrated into the PG should you introduce the Vegetable Glycerin.

Strategy 2: Thermal Processing and Mixing Time

When creating high-VG batches, the entire mixture should be processed at elevated temperatures. Heated VG is less viscous and has slightly better solvent capacity than cold VG.

Maintaining the batch at 45°C to 55°C during the mixing phase ensures that the menthol remains fully dissolved while it is being dispersed throughout the heavy VG phase. Furthermore, ensure adequate mixing time. High-shear mixing is often necessary to ensure absolute homogeneity in high-VG blends. If pockets of higher menthol concentration remain due to poor mixing, those pockets will become nucleation sites for crystallization later.

Strategy 3: Utilizing Co-Solvents

Sometimes, the required PG ratio is simply too low to support the desired menthol load. In these cases, formulators must turn to auxiliary co-solvents.

Small percentages of Ethyl Alcohol (Ethanol) or Triethyl Citrate can significantly boost the solvent capacity of a high-VG base without drastically altering the Vg/Pg ratio on the label. Ethanol is an excellent solvent for menthol. However, it increases throat hit and can affect flavor, so it must be used judiciously (typically under 5%).

Citation 3: Rowe, R. C., Sheskey, P. J., & Quinn, M. E. (Eds.). (2009). Handbook of Pharmaceutical Excipients (6th ed.). Pharmaceutical Press. (Source for standard industrial mixing practices and properties of co-solvents like ethanol in formulations).

Industrial E-Liquid Mixing Process

Section 6: Troubleshooting and Best Practices for Manufacturers

Even with robust formulations, issues can arise post-production.

6.1 The Winter Shipping Protocol

The most common complaints regarding crystallized menthol occur during winter months in northern hemispheres. If you know your product will be subjected to freezing temperatures during transit, you must stress-test your formulation.

• QC Recommendation:Place samples of your high-menthol/high-VG final product in a refrigerator (approx 4°C) for 48 hours, and a freezer (-10°C) for 24 hours. If they turn solid white or develop needles, they will crash during winter shipping. You must either lower the menthol content or increase the PG/co-solvent ratio for winter batches.

6.2 Batch Recovery: Can it be fixed?

If a batch crystallizes in storage, it is sometimes recoverable, though not ideal.

• Gently reheatthe entire batch to roughly 50°C until completely clear.
• Agitate vigorouslyto ensure re-dissolution.
• Crucial Step:You must add more solvent. If it crashed once, it will crash again when it cools unless the composition changes. Adding a small amount of additional PG or PG-based flavor concentrate while heated can stabilize the mixture upon cooling.

Section 7: The Future of Mentholated High-VG E-liquids

The market demand for high-VG is not slowing down, nor is the desire for intense cooling sensations. The industry is responding with innovations beyond simple menthol crystals.

We are increasingly seeing the adoption of synthetic cooling agents (such as WS-3, WS-23, and others) used in conjunction with, or sometimes replacing, traditional menthol. These agents often have different solubility profiles and can provide intense cooling without the same risk of crystallization at high concentrations in VG, although they lack the characteristic “minty” taste of menthol.

Furthermore, regulatory bodies are paying closer attention to product stability. E-liquids that change physical state on the shelf may face scrutiny regarding product consistency and consumer safety standards. Mastering solubility is no longer just about flavor; it is becoming a compliance necessity.

Citation 4: U.S. Food and Drug Administration. “Premarket Tobacco Product Applications and Recordkeeping Requirements (Final Rule).” FDA.gov. (Relevant context regarding product stability and consistency requirements for manufacturers).

Conclusion: Partnership in Precision

Menthol crystallization in high-VG e-liquids is a predictable chemical phenomenon, not an unavoidable nuisance. It is a boundary set by thermodynamics that can be managed through intelligent formulation, appropriate thermal processing, and rigorous quality control testing.

The key is recognizing that VG is a poor solvent for menthol and compensating for that weakness through PG pre-dissolution or the use of co-solvents.

As a manufacturer of premium fragrance and flavor compounds, we do more than just supply ingredients; we provide the technical expertise required to utilize them effectively. We understand the delicate balance between achieving the desired sensory impact and maintaining a stable, marketable product. Don’t let solubility limits dictate your product quality. Partner with experts who understand the science behind the sensation.

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