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Aparita Bhandari, front, with her family as a child in New Delhi, was intent in recreating her Nani’s mango pickle recipe after striking out with store-bought options in Canada.

Mangoes were one of the few reasons to look forward to the sweltering summers when I was growing up in New Delhi. The month of May meant the arrival of the fragrant fruit. It also meant the appearance of a large porcelain jar on the balcony at the house of my Nani, or maternal grandmother, its mouth covered with a muslin cloth and inside, small chunks of raw mango fermenting in the sun. Nani made the best mango pickle.

We had to be careful around the jar for the two or three weeks it sat in the blistering heat. Not even a drop of water could go near it and the prospect of accidentally knocking it over was terrifying. When it was ready, the pickle was portioned out among the family. Even a whiff of the pickle – tart pieces of mango mellowed in the pungent mustard oil, dotted with flecks of fennel and nigella seeds – was enough to make my mouth water.

After moving to Canada in 1998, I tried many commercial pickles, tempted by brand names such as Mother's Recipe. That label was a false promise. None of the store-bought pickles had the complexity of flavours of Nani's pickle. They were also much more salty, leaving a bad taste in my mouth.

One day, I noticed fresh mangoes at an Indian grocery store and thought I'd try making mango pickle myself. But when I mentioned the idea to an acquaintance who cans fruits and vegetables every summer, she raised an eyebrow: "Aren't Indian pickles made in oil? They aren't safe. You know. Botulism."

Since she'd turned up her nose at my turmeric-stained fingernails and curry-smelling clothes in the past, I figured she didn't know much about the actual process of making Indian pickles. So after making a few phone calls to Nani and scouring dozens of websites for Indian pickle recipes and best preservation practices, I made my first batch of mango pickle, the way Nani made it, with some minor adjustments.

Still, the fear of poisoning myself lingered. I noticed that my bottle of mustard oil, used to prepare many Indian pickles and other South Asian foods, carried a warning on a sticker: For external use only.

I called Keith Warriner, a professor in food microbiology in the Department of Food Science at the University of Guelph. He reminded me that fermenting and preserving fruits and vegetables has been practised by different cultures since early civilization. "So your grandmother would have learned it from her grandmother and they know how to look out for the bad things by experience," he says.

The list of "bad things" could range from gross but harmless spoilage to dangerous pathogens such as Clostridium botulinum. In the case of botulism, it's the toxin produced from the bacteria that is harmful, not the bacteria itself, says Brigitte Cadieux, a postdoctoral fellow in McGill University's Department of Food Science and Agricultural Chemistry.

"That toxin is easily deactivated by heat, which is what you do in canning. But sometimes, you can get spores, which are heat-resistant," says Cadieux, which means you need to kill them another way. "One way we deal with it is by lowering the pH. The spores will never germinate in an acidic environment. I am French-Canadian and I do canning. We have many traditional recipes where we add vinegar to the pickling process to lower the pH."

Many Indian pickles also use vinegar in their preparation process, but not mango pickled in mustard oil. So it's true that the oil creates an anaerobic environment that's perfect for Clostridium botulinum to produce toxins. This is where traditional knowledge comes in: In my Nani's recipe, mango chunks aren't submerged in oil until they are washed, dried, cut, salted and then further dried in the sun with the addition of spices such as turmeric powder and fenugreek, fennel and nigella seeds.

The salting process is important to take out moisture, where bacteria can flourish, and that, along with the acidity of the raw mango, might be enough to address some concerns, Warriner says. "Trouble is that sometimes people take traditional recipes and tinker with them," he says. "You're concerned about your salt intake, so you reduce the salt. But you need the salt to deal with the bacteria."

I shouldn't have adjusted Nani's recipe: Grandma generally knows best.

Cadieux doesn't condemn home preservation, but emphasizes that the risk of botulism is real and serious. Depending on the amount of toxin ingested, it can lead to death. "I certainly can't give the green light on the product, but it's possible that the growth of Clostridium botulinum is limited in this product by a combination of different factors," she says. "There's no way to know for sure unless measurements are made."

Home preservers can calibrate their recipes with the help of pH paper to measure acidity and a refractometer to measure salinity – the former costs less than $10 at a hardware store, while the latter can be bought online for about $30. I've picked up both tools, since it can't hurt to be more careful.

As far as mustard oil is concerned, Health Canada does consider it unacceptable for use as a food substance. That's because it "contains erucic acid at levels that would exceed the limits specified in regulations," the department explains in a written statement.

High levels of erucic acid can be harmful, especially for young children, says Warriner, who adds this also used to be a problem with rapeseed oil. But then, with some help from Canadian research, new strains of rapeseed were developed with lower levels of erucic acid: We know the far-less-bitter oil expressed from those strains as canola.

Mustard also contains a high level of isothiocyanate, which is a natural antimicrobial, Warriner says. "It's what gives mustard its burn and that pungent flavour. It's a good preservative," he says. "I can't imagine [mustard oil] would be harmful if ingested in small doses. Like they say with everything, 'Moderation is key.'"

That batch of mango pickle I made was worthy of Nani's recipe. Tart and pungent – just a smidgen of it livened up a simple meal of lentil and rice. So when I spy another batch of raw mangoes at the Indian grocery store, I am definitely going to buy a bunch.

I plan to make my oil-based pickle again, although with more reverence for science along with my love for my grandmother.

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