Milk is a cornerstone of the Western diet, a cosy symbol of comfort and nourishment.

Kids start the day with sloshing bowls of cereal, slurping the sweet puddle of milk that remains when parents’ backs are turned. At school, the warm bottles of milk endured by previous generations have been replaced by chilled cartons, and malty Milo is the scent of snack times. And before bed, it’s the soporific spell of a warm glass of milk that sends us on our way.

These days, while many Australians still count a litre of milk as a kitchen staple, others have moved beyond the cow, with a new study by the CSIRO revealing that one in six of us opt for plant-based options.

The question of ‘soy, almond or oat?’ has replaced ‘skim or full-cream?’, and that’s just a decision for your flat white.

The plant-based milks – alt-milks or ‘mylks’ as they’re known – lining supermarket shelves are made from anything from nuts (almond, cashew, hazelnuts) to seeds (quinoa, hemp), legumes (soya), fruit (coconut) and grains (rice, oat). They’re a godsend for people with a dairy allergy or lactose intolerance and a plan B for vegans and those who eschew animal products.

The scant selection of plant-based milks that led the charge a decade ago weren’t too convincing. They split, they curdled, some were loaded with sugar. Now alt-milks are so specialised there are low-fat and low-sugar versions with special barista additions engineered for heating and frothing.

This growing niche is propelled by the spread of vegan and flexitarian diets championed by millennials and gen Z, who are eager to explore alternatives to the conventional staples their parents grew up with. And food brands are answering the call to raise their mylk game.

“In many ways, the global barista community leads cultural changes in coffee and milk consumption, and were early adopters of almond and soy milk and now oat milk,” says Greg Steltenpohl, founder and CEO  of Califia Farms. Specialising in plant-based products, the company recently launched a new Oat Barista Blend, adding to the portfolio it started in 2012 with almond milk. Oat milk is on the rise elsewhere, too.

Stuart Forsyth, a London-based Aussie and co-founder of Keep Cup, heads up Minor Figures, specialising in artisan cold-brew and iced coffee and now oat milk. “We chose to produce our own oat milk because it’s the best to pair with coffee in terms of mouthfeel and flavour. That said, we’re not an oat milk company,” says Forsyth.

“We believe dairy is the status quo because of its historical application, but it’s not the gold standard in coffee,” he says.

When it comes to the question of sustainability, comparisons aren’t always clear-cut. An Oxford University study last year found that producing cow’s milk results in almost three times the greenhouse gas emissions of any alt-milk, though impact varies between countries according to climate and the transportation involved for the products. But that’s not the whole story.

Oat and soy are the least water intensive crops, but it takes around 4.5 litres of water to produce one almond and in California, the source of 80 per cent of the world’s almond crop, that’s 10 per cent of the supply in the drought-stricken state. Soybean production, meanwhile, has driven deforestation in the Amazon. The UK imports half of its soybeans from  Brazil, but in Australia soy milk is made with our domestic crop.

And how do alt-milks stack up nutritionally? Sydney-based accredited dietitians Alex Parker and Anna Debenham, who founded nutrition consulting business The Biting Truth, say not all alt-milks are created equal. “The nutritional qualities of plantbased milks vary greatly,” they say.

“If you’re choosing plant-based milks, it’s essential to ensure they’re fortified with calcium. In terms of nutrients, calcium-fortified soy is the best substitute for cow’s milk. Check the ingredient list to ensure the milk has no added sugars and avoid products with fillers or additives.”

Here again almond milk has come under fire, with some versions having as little as two per cent almond content along with sugar and emulsifier.

While plant-based lifestyles are far more mainstream than ever before, Forsyth believes veganism remains counter-culture in the current climate.

“Veganism is one of our last subversions of a society heading in the wrong direction,” he says. “This gives the movement an attitude – plant-based is punk.”

For now, he says plant-based is a protest,pending further research, but a glass of oat milk may not be so radical when our great-grandchildren are dipping their cookies in mylk.