The game is afoot! UK charity Crimestoppers is enlisting the help of the Great British public to sniff out cannabis farms. To aid the public in their undercover work they’ve been handing out scratch and sniff panels. These give people an idea of what living, growing cannabis smells like – Crimestoppers describes it as a sickly, sweet smell as opposed to the more acrid aroma when it’s smoked (we at Chemistry World are relying on testimony from local a Cambridge councillor here!).

Tests indicate that fresh cannabis has an aroma like freshly cut vegetation and grass with a slightly sickly sweet undertone!

Crimestoppers is warning that cannabis cultivation is a growing trend in the UK with the number of farms uncovered in 2012 up 15% on the previous year. The charity is working with the police to try to tackle the increase in residential farms, where people often grow the plants hydroponically in attics using heat lamps and high intensity lighting. The police has said that cannabis cultivation is fuelling organised crime, while the UK’s energy regulator says that the cost of electricity stolen by these farms may be costing the economy as much as £400 million each year.

Lucy Reid, campaign manager at Crimestoppers, says the idea came from the Dutch police. They ran a similar campaign and as a result there was a 45% rise in cannabis farms sniffed out in Amsterdam. She points out that the scratch and sniff panel doesn’t contain any tetrahydrocannabinol (THC) – the psychoactive compound in cannabis and also the inspiration for a number of pharmaceutical drugs to treat illnesses such as multiple sclerosis.

The scratch and sniff card set us at CW Towers to thinking about how they were able to recreate the smell of fresh cannabis. To try to find out I spoke with JanCees Neef at the Edge Factory in the Netherlands, whose company produce the scratch and sniff cannabis panels. Unfortunately, he’s not able to tell us that much about the production process as it’s a company secret. However, he did tell us that the Dutch police deliver cannabis plants to them and that they quickly process them, to extract an oil from the plants – Neef says that this needs to be done as fast as possible because oil made from wilted plants smells like rotten eggs, giving people a nasty surprise when they scratch and sniff. This cannabis oil is then microencapsulated – Neef won’t say more about the process – and printed onto cards. Neef does say, however, that the microencapsulation technology preserves the smell for a couple of years.

Microencapsulation has its roots in carbonless copy paper, developed back in the 1960s to put an end to the messy carbon papers that turned your hands black. In this case microencapsulated inks were stored in the paper and burst open when the typewriter’s typebars hit the paper. While Edge won’t tell us how they encapsulate their oil, it’s possible to take an educated guess at the type of process used.

There are numerous ways of microencapsulating compounds and most have been developed by the cosmetics industry to deliver their latest wrinkle defying elixir. Scratch and sniff panels often use polymers like polyoxymethylene urea. The oil and polymer are mixed together at high speed to produce droplets of oil 15–20µm in size, suspended in the polymer solution. A catalyst is then added to  crosslink the polymers, sealing the oil inside the microcapsules. The microencapsulated oil droplets are then washed to remove leftover polymer and oil, and then processed to form a slurry for printing. Once printed onto a panel, scratching the card bursts some of these microcapsules, releasing whatever smelly compound the manufacturer desires – in Crimestoppers’ case the scent of cannabis plants.

In the office we were also intrigued by which volatiles give fresh cannabis its distinctive smell. Again, this is something Neef couldn’t tell us unfortunately, but there is some information out there. Apparently, cannabis’ smell is the product of more than 100 terpenoids, including eucalyptol, linalool and pinene. What’s also interesting is Reid’s insistence that the scratch and sniff panels don’t contain any THC, but obviously still contain enough of the smelly terpenoids to provide a rough approximation of the odour of growing cannabis. Given that many of the terpenoids volatilise at the same temperatures as THC and that they’re both fat-soluble it’s difficult to immediately see a simple way of processing the oil to exclude THC, while keeping in those aromatic, smelly terpenoids. And my internet searches on the question of THC extraction have been throwing up all the wrong results!

Patrick Walter

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Scratch and sniff detectives wanted to hunt down cannabis farms, 4.5 out of 10 based on 2 ratings
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