A laser into the bottle: Detecting toxic methanol without breaking the seal

Counterfeit alcohol is often framed as a criminal issue, but it is also a global public health concern. Every year, methanol-contaminated spirits cause hundreds of deaths and leave many more people with permanent health damage, including blindness. In some cases, the consequences unfold rapidly: in 2024, six tourists in Laos died after consuming alcohol later found to contain dangerous levels of methanol.

Despite the scale and persistence of this problem, detecting methanol has remained surprisingly difficult outside specialist laboratories. Conventional tests require trained personnel, controlled conditions and expensive analytical equipment—barriers that limit routine screening and leave gaps in protection.

Now, researchers at the University of St Andrews in the UK and the University of Adelaide in Australia have developed a striking alternative: an optical method that can identify methanol in sealed bottles of spirits without ever opening them. Their work, points towards a new generation of rapid, non-invasive safety testing.

Seeing through the glass

At the heart of the innovation is Raman spectroscopy, a well-established technique that uses laser light to probe the molecular composition of a substance. When light interacts with molecules, a small proportion scatters in a way that carries a chemical “fingerprint”—allowing scientists to determine what compounds are present.

In principle, this makes Raman spectroscopy ideal for identifying contaminants such as methanol. In practice, there has been a major obstacle: glass bottles.

“The bottle itself produces strong optical signals that tend to overwhelm the signal from the liquid inside,” explains Ané Kritzinger, lead author of the study. “And if the glass is coloured—as it often is for spirits like whisky—the problem becomes even worse due to fluorescence.”

Previous attempts to apply Raman spectroscopy to sealed drinks have therefore been limited largely to clear glass containers. The new technique overcomes this limitation with a clever combination of optical engineering.

By shaping the laser beam into a ring pattern and subtly adjusting its wavelength during measurement, the researchers were able to suppress interference from both the glass and the bulk liquid. This allowed the faint, distinct signature of methanol to emerge. The result is a method capable of detecting methanol through green, brown and blue bottles, as well as clear glass.

Sensitivity and safety

Perhaps most important aspect is the sensitivity of the technique. The researchers report a detection limit of around 0.2 per cent methanol, an order of magnitude below the threshold considered dangerous for human consumption.

“In practical terms, this means we can detect methanol at concentrations far below those associated with toxic effects,” says Kritzinger. “It provides a meaningful safety margin.”

This capability could transform how alcohol safety is monitored. Instead of relying on occasional laboratory testing or post-incident investigation, regulators and distributors could screen products directly in the field, rapidly and non-destructively.

“It opens the door to routine checks at multiple points in the supply chain,” says Graham Bruce, co-author of the study. “You could imagine testing shipments at ports, warehouses, or even retail outlets.”

Methanol contamination arises most commonly from the production of counterfeit or illegally distilled spirits. Unlike ethanol—the alcohol intended for consumption—methanol is highly toxic. Even small amounts can lead to metabolic acidosis, neurological damage and blindness.

The World Health Organization has repeatedly highlighted methanol poisoning as a significant international issue, particularly in regions where regulatory oversight is inconsistent. Estimates suggest that tens of thousands of deaths have occurred over the past decade alone, with incidents reported in nearly 80 countries. One of the challenges is that methanol-contaminated products can look, smell and taste similar to legitimate spirits. Without reliable testing, detection is difficult until after exposure has occurred.

Beyond alcohol: A broader platform

Non-invasive optical analysis could be applied to a wide range of sealed products, including pharmaceuticals, cosmetics and perfumes. In industries where counterfeiting is a growing concern, the ability to verify contents without damaging packaging is particularly valuable.

As with many experimental techniques, the next question is scalability. Raman spectroscopy systems are already widely used in laboratories, but adapting them for field use requires careful consideration of cost, portability and robustness. Advances in compact laser systems and optical components are making this increasingly feasible.

There are also logistical considerations. For example, integrating such systems into inspection workflows at ports or within distribution networks would require coordination between regulators, manufacturers and retailers. Nonetheless, as optical technologies become more compact and affordable, their use outside traditional laboratories is expanding—from handheld spectrometers to smartphone-based diagnostic tools.