Vegetable Glycerine: A Comprehensive Overview

1. Introduction: What Is Vegetable Glycerine?

Vegetable Glycerine (VG), also known as glycerol, is a clear, odourless, and viscous liquid derived from plant oils—most commonly palm, soy, or coconut oil. It is a type of sugar alcohol with a naturally sweet taste and is widely used across multiple industries due to its moisturising, solvent, and sweetening properties.

Chemical Name: Glycerol
IUPAC Name: Propane-1,2,3-triol
Molecular Formula: C₃H₈O₃
Molecular Weight: 92.09 g/mol

2. How Is Vegetable Glycerine Made?

Vegetable glycerine is typically obtained through a process known as hydrolysis, transesterification, or saponification, depending on the source oil and intended use.

2.1 Hydrolysis Process

1. Plant oils (e.g., palm or soy oil) are heated under pressure with water.
2. The fatty acids separate from the glycerol backbone.
3. The glycerol is then purified through distillation.

2.2 Transesterification (Biodiesel Production By-Product)

In biodiesel production, plant oils react with an alcohol (usually methanol) in the presence of a catalyst (such as sodium hydroxide), producing methyl esters (biodiesel) and crude glycerol as a by-product. This crude glycerol is then refined and purified.

2.3 Saponification

This traditional soap-making process combines fats with a strong base (e.g., sodium hydroxide), resulting in soap and glycerol. The glycerol is then separated and purified.

Table 1: Comparison of Production Methods

3. Chemical Properties of Vegetable Glycerine

Vegetable glycerine exhibits a number of unique physical and chemical properties that make it highly versatile.

3.1 Physical Properties

3.2 Chemical Behaviour

• Trihydric Alcohol: Contains three hydroxyl (–OH) groups.
• Stable Compound: Non-reactive under normal conditions but may oxidise slowly in air.
• Combustibility: Burns with a faint blue flame; decomposes at high temperatures.

4. Applications of Vegetable Glycerine

Vegetable glycerine’s hygroscopic and non-toxic nature lends it to a broad range of applications in food, pharmaceuticals, cosmetics, and more recently, vaping.

4.1 Food Industry

• Humectant: Retains moisture in baked goods and confectionery.
• Sweetener: Used in low-sugar and diabetic products (GI ~3).
• Solvent: For flavourings and food colourants.
• Preservative: Extends shelf life due to antimicrobial effects.

4.2 Pharmaceuticals and Personal Care

• Topical Moisturiser: Used in creams, lotions, and soaps for its hydrating effect.
• Capsule Fillers: Acts as a plasticiser and stabiliser in soft gel capsules.
• Suppositories: Employed as a laxative base.
• Mouthwashes and Toothpaste: Adds smooth texture and sweet flavour.

4.3 Industrial Applications

• Antifreeze and Coolants: As a non-toxic alternative to ethylene glycol.
• Lubricants: Especially in food-safe or eco-sensitive environments.
• Plastic Manufacturing: Used in the production of biodegradable plastics.

4.4 Vaping and E-Liquids

Vegetable glycerine is a core ingredient in most e-liquids, often blended with propylene glycol (PG). Its thick consistency and vapour-producing capabilities make it ideal for sub-ohm vaping.

VG vs PG in E-liquids

Advantages in Vaping

• Produces dense vapour clouds.
• Provides a smooth throat hit, ideal for high-wattage vaping.
• Generally hypoallergenic, reducing risk of irritation.

Considerations

• VG-heavy liquids can clog coils and reduce wick efficiency.
• Requires high-powered devices due to viscosity.

Figure 1: VG/PG Ratio Effects on Vaping Characteristics

VG Content (%) →        50       70       80       100
--------------------------------------------------------
Vapour Density        |  Medium | High   | Very High | Extreme
Throat Hit            |  Strong | Mild   | Smooth    | Very Smooth
Flavour Intensity     |  High   | Medium | Mild      | Mildest
Coil Compatibility    |  High   | Medium | Low       | Lowest

Note: Optimal VG/PG ratio is subjective and depends on device and personal preference.

5. Safety and Toxicity

Vegetable glycerine is classified as Generally Recognised as Safe (GRAS) by the US FDA and approved by the European Food Safety Authority (EFSA). However, inhalation via vaping is relatively new, and long-term studies are ongoing.

Known Risks

• Lipoid Pneumonia: Rare but possible with excessive inhalation of oils.
• Contamination Risk: Industrial-grade VG may contain impurities if not properly purified.
• Thermal Decomposition: At high temperatures (>280°C), can break down into acrolein, an irritant.

6. Environmental and Ethical Considerations

As VG is plant-derived, its sustainability depends on the source oil. For instance:

• Palm oil-based VG raises deforestation concerns.
• Soy and coconut oil alternatives are often more sustainable.

Consumers increasingly seek RSPO-certified or organic VG to reduce environmental impact.

Conclusion

Vegetable glycerine is a multifaceted compound with a rich profile of chemical properties and diverse applications. From food and pharmaceuticals to personal care and vaping, its non-toxic and hygroscopic nature has made it indispensable in modern industries.

While widely regarded as safe, users—especially vapers—should remain informed about the quality, purity, and sourcing of the VG they consume. With growing attention to sustainability and health, the role of VG is set to evolve further in the years ahead.