Migration Testing for Food Packaging: OML, SML & Food Simulants Explained

Migration testing is the single most important quality control measure in food packaging safety. It measures the transfer of chemical substances from packaging material into the food it contains -- or more precisely, into standardised food simulant liquids that replicate the chemical behaviour of different food types. In India, migration testing is governed by IS 9845:1998 and mandated by the Food Safety and Standards (Packaging) Regulations, 2018.

Despite its importance, migration testing remains poorly understood outside of laboratories and quality control departments. This guide explains the science behind migration testing in practical terms, covers the regulatory requirements, and provides guidance on interpreting test reports -- whether you are a packaging manufacturer, a food business owner, or a wholesale buyer.

What Is Migration?

Migration is the mass transfer of low-molecular-weight substances from packaging material to food. Every packaging material contains substances beyond the base polymer or fibre: plasticisers that make plastic flexible, antioxidants that prevent degradation, UV stabilisers, colourants, residual monomers from the polymerisation process, and processing aids. These substances can move into the food that contacts the packaging, driven by diffusion (concentration gradient between packaging and food), temperature (higher temperatures accelerate migration), time (longer contact increases total migration), and the chemical affinity between the migrating substance and the food (fatty foods extract more substances from plastics than aqueous foods).

Migration is not hypothetical. It is a measurable, quantifiable process that occurs to some degree in every food-packaging interaction. The regulatory question is not whether migration occurs, but whether it occurs within safe limits.

Overall Migration Limit (OML)

The Overall Migration Limit is the total quantity of all non-volatile substances that transfer from the packaging material to the food simulant under specified conditions. Under IS 9845 and the FSSAI Packaging Regulations, the OML for all food contact plastics in India is 60 mg/kg of food (or equivalently, 10 mg/dm2 of the packaging surface area).

This means that for every kilogram of food in contact with the packaging, no more than 60 milligrams of total material should transfer from the packaging. This limit does not distinguish between harmful and harmless migrating substances -- it is a blanket safety threshold based on the principle that minimising total migration minimises the risk of exposure to any individual harmful substance.

How OML Is Measured

The test procedure under IS 9845 involves cutting the packaging material to a defined surface area, immersing it in the appropriate food simulant at the prescribed temperature for the prescribed duration, removing the packaging material and evaporating the food simulant, and weighing the non-volatile residue left after evaporation. The residue weight, expressed as mg per kg of simulant (or mg per dm2 of packaging surface), is the overall migration value.

Specific Migration Limits (SML)

While OML captures the total migration, Specific Migration Limits target individual substances of concern. The FSSAI Packaging Regulations, 2018, Schedule I, lists substances with individual migration limits:

Substance	Source / Relevance	SML (mg/kg food)
Lead (Pb)	Colourants, stabilisers, glass, ceramic glazes	1.0
Cadmium (Cd)	Colourants, PVC stabilisers	0.002
Bisphenol A (BPA)	Polycarbonate, epoxy can linings	0.6
DEHP (phthalate)	PVC plasticiser	1.5
DBP (phthalate)	PVC plasticiser, printing inks	0.3
BBP (phthalate)	PVC plasticiser	30.0
Vinyl chloride monomer	PVC packaging	0.01
Acrylonitrile	ABS, SAN, and acrylonitrile copolymers	0.02
Formaldehyde	Melamine-formaldehyde tableware	15.0
Melamine	Melamine-formaldehyde tableware	2.5

SML testing uses the same food simulants and contact conditions as OML testing, but the analytical methods are different. Instead of measuring total non-volatile residue, the laboratory uses specific analytical techniques (gas chromatography, liquid chromatography, atomic absorption spectroscopy, or ICP-MS) to identify and quantify individual substances.

Food Simulants: Replicating Real Food Conditions

Testing migration with actual food is impractical because food is chemically complex and results would vary with every batch. Instead, standardised food simulants are used. Each simulant replicates the migration behaviour of a food category:

Food Simulant	Represents	Examples of Foods
Distilled water	Aqueous foods with pH above 4.5	Plain water, tea, coffee, milk, dal, sambar, rasam
3% acetic acid (w/v)	Acidic foods with pH below 4.5	Pickles, lemon juice, curd, buttermilk, tomato sauce, tamarind chutney
15% ethanol (v/v)	Alcoholic beverages and foods containing alcohol	Beer, wine, spirits, food preparations with alcohol
n-Heptane or rectified olive oil	Fatty foods	Ghee-laden curries, fried items, butter chicken, oil-based pickles, cheese

The food simulant chosen for a migration test must match the intended use of the packaging. A container designed for biryani delivery should be tested with both the fatty food simulant (because biryani contains oil and ghee) and the aqueous food simulant (because it also contains water-based gravy). A paper cup for chai should be tested with distilled water as the primary simulant.

Test Conditions: Temperature and Time

Migration is temperature and time dependent. The test conditions must replicate how the packaging will actually be used:

Intended Use Condition	Test Temperature	Test Duration
Long-term room temperature storage	40 degrees C	10 days
Short-term room temperature contact (less than 24 hours)	40 degrees C	24 hours
Hot-fill applications (food filled above 66 degrees C)	70 degrees C	2 hours
Boiling or near-boiling contact	100 degrees C	30 minutes
Microwave heating	100 degrees C or 175 degrees C (depending on protocol)	15-30 minutes
Refrigerated storage	5 degrees C	10 days

The principle is conservative: testing at higher temperatures and longer durations than actual use provides a safety margin. If a container passes migration testing at 40 degrees C for 10 days, it is considered safe for any room-temperature application of shorter duration.

How to Read a Migration Test Report

A properly issued migration test report from a NABL-accredited laboratory will contain several key sections. The sample description identifies the packaging product tested (material, size, colour, batch, manufacturer). The test method section cites the standard (IS 9845 or equivalent). The food simulants used and the contact conditions (temperature and duration) are listed. The results section shows numerical values for OML and any SML parameters tested, expressed in mg/kg or mg/dm2. The conclusion states whether the sample complies with the applicable limits.

What to Check as a Buyer

• The test report is from a laboratory with current NABL accreditation (check the accreditation number)
• The sample described matches the product you are buying (same material, size, colour)
• The food simulants tested are appropriate for your intended use (e.g., fatty simulant for containers used with oily food)
• The test conditions are appropriate for your use case (e.g., hot-fill conditions for containers receiving hot food)
• OML result is below 60 mg/kg
• All SML results are below their respective limits
• The report date is within the last 12 months

Common Failures and Their Causes

Understanding why migration tests fail helps buyers assess product quality:

• OML failure in plastic products: Usually caused by excess plasticiser, low-quality raw material with high additive content, or recycled material with unpredictable composition.
• Colour migration: Non-food-grade pigments or dyes used in coloured packaging. Common in cheap coloured plastic plates and cups.
• High lead or cadmium: Contaminated raw materials, industrial-grade (not food-grade) recycled plastic, or non-food-grade printing inks.
• OML failure in paper products: Recycled paper with printing ink residues, or paper with excessive chemical sizing agents.
• Formaldehyde migration from melamine: Under-cured melamine tableware or poor-quality melamine resin.

Products from established manufacturers using virgin, food-grade raw materials and controlled manufacturing processes rarely fail migration testing. Products of unknown origin, sold without documentation, and priced significantly below market rates carry a higher risk of failure.

International Comparison

India's migration limits are broadly aligned with international standards, though some differences exist. The EU's OML under Regulation 10/2011 is also 60 mg/kg, identical to India's IS 9845. The US FDA uses specific migration limits for individual substances rather than an overall migration limit. Japan's Food Sanitation Act sets an OML of 30 mg/litre for some materials, stricter than India's limit. India is expected to harmonise further with EU standards in upcoming revisions of IS 9845 and the FSSAI Packaging Regulations.

For food packaging intended for export, the migration testing must comply with the destination country's requirements, which may be stricter than Indian standards.