Sorbitan Monostearate (SMS), known commercially as Span 60 and assigned the food additive code E491, is a non-ionic, lipophilic emulsifier synthesized via esterification of sorbitol with vegetable-based stearic acid. For R&D chemists and quality engineers, SMS is more than a blending agent — it is a structural stabilizer with well-defined molecular behavior.
For food application profiles, dosage limits by product category, and regulatory compliance tables, see our Food Applications & Regulatory Limits Guide.
1. Chemical Identity and Molecular Structure
| Parameter | Value |
|---|---|
| Chemical Name | Sorbitan Monostearate |
| Trade Name | Span 60 |
| E-Number | E491 |
| CAS Number | 1338-41-6 |
| Molecular Formula | C₂₄H₄₆O₆ |
| Molecular Mass | 430.62 g/mol |
| Fatty Acid | Stearic Acid (C18, saturated) |
| HLB Value | 4.7 |
| Melting Point | 50–52 °C |
| Acid Value | ≤ 10 mg KOH/g |
| Saponification Value | 147–157 mg KOH/g |
| Hydroxyl Value | 235–260 mg KOH/g |
| Physical Form (25°C) | Cream to tan waxy beads, flakes, or powder |
Amphiphilic Architecture
The molecule consists of a sorbitan head (a cyclic ether derived from sorbitol dehydration) and a stearic acid tail (C18 saturated chain). The sorbitan ring provides the hydrophilic anchor via residual hydroxyl groups, while the C18 tail embeds deeply into lipid phases. This asymmetry is the basis for all of SMS’s functional properties.
HLB 4.7: What It Means
At HLB 4.7, SMS is firmly in the low-HLB, oil-soluble range. It stabilizes Water-in-Oil (W/O) emulsions by reducing interfacial tension at the oil-water boundary. It is insoluble in cold water, dispersible in hot water, and soluble in ethanol, ether, and mineral oils above 50°C.
2. alpha-Crystalline Stabilization
In lipid-rich systems (shortenings, whipped creams, chocolate), SMS promotes and stabilizes the alpha-crystalline polymorph of fats. This specific crystal form is desirable because:
- It creates a flexible, resilient fat crystal network that entraps air cells efficiently.
- It delivers superior overrun in whipped products compared to beta-prime or beta crystals.
- It resists polymorphic transition during temperature cycling, preventing the graininess that occurs when fats recrystallize into the beta form.
This mechanism is distinct from the crystal modification performed by Sorbitan Tristearate (Span 65, E492), which targets cocoa butter specifically. SMS provides broader fat-phase stabilization across bakery and dairy systems.
3. Synergy Chemistry: Span 60 + Polysorbates
Due to its low HLB, SMS has limited emulsifying power when used alone in O/W systems. The industry-standard approach pairs it with high-HLB Polysorbates:
| SMS + Polysorbate Pair | Tween HLB | Combined HLB Range | Best For |
|---|---|---|---|
| SMS + Polysorbate 60 (Tween 60) | 14.9 | 4.7–14.9 | Bakery, whipped toppings, O/W cakes |
| SMS + Polysorbate 65 (Tween 65) | 10.5 | 4.7–10.5 | Confectionery coatings, chocolate |
| SMS + Polysorbate 80 (Tween 80) | 15.0 | 4.7–15.0 | Ice cream, dairy substitutes |
Matching the C18 stearic chain of SMS with the C18 stearic chain of Polysorbate 60 produces the most ordered interfacial film — the chains pack tightly, maximizing emulsion stability and minimizing the total surfactant load required.
4. Processing Requirements
Thermal Dispersion
SMS must be pre-dissolved in the heated oil phase before emulsification:
- Heat the fat/oil phase to 55–65°C (10–15°C above SMS melting point).
- Add SMS and stir until fully dissolved and clear.
- Maintain the water phase at the same temperature before combining.
- Cool under controlled shear — slow cooling yields fine, stable crystals; rapid cooling produces a coarser texture.
Hydration Compensation
SMS increases moisture retention in dough systems. If the dough feels stiff after adding SMS, the formulation likely needs a 2–5% increase in water content to compensate for the emulsifier’s water-binding effect. This is normal and does not indicate product failure.
5. Frequently Asked Questions
Q: Can Sorbitan Monostearate be used in cold-process manufacturing?
No. SMS is a waxy solid with a melting point above 50°C. It will not disperse effectively in cold oil or cold water. It must be melted into the heated fat phase prior to emulsification.
Q: Is E491 suitable for vegan, Halal, or Kosher products?
Yes — when sourced from vegetable-based stearic acid (palm or soy) and corn/wheat-derived sorbitol. SMS is suitable for vegan, Halal, and Kosher certification. However, because it is a chemically synthesized ester, it does not qualify for “clean-label” declarations that prohibit E-numbers.
Q: Why does my dough feel stiff after adding SMS?
SMS complexes with amylose in wheat starch and binds water. If dough becomes excessively stiff, you have either exceeded the recommended dosage or not increased formula hydration to compensate. See our Food Applications & Regulatory Limits Guide for category-specific dosage limits.
Q: What’s the difference between SMS (Span 60) and Sorbitan Tristearate (Span 65)?
Span 60 is a monoester (one stearic acid chain); Span 65 is a triester (three stearic acid chains). Span 65 has a much lower HLB (2.1) and is primarily used for crystal modification in chocolate and yeast coating. Span 60 (HLB 4.7) is more versatile and is the standard choice for bakery, whipped toppings, and general W/O emulsification.
Summary
Sorbitan Monostearate (E491 / Span 60) is defined by three molecular properties: an HLB of 4.7, an alpha-crystal-stabilizing polymorphic effect, and a saturated C18 chain that packs tightly with Polysorbate 60. These properties make it the most widely specified solid Span for food and industrial emulsification.
For product-level dosage limits and application protocols, consult our Food Applications & Regulatory Limits Guide.
Contact FoodEmul.com for technical data sheets, COA, or samples.
