As the mercury rises in India, the hottest question of the season is, how do you make ice cream?

The recipe for everyone’s favourite summer treat has two of the country’s biggest packaged food companies, Hindustan Unilever and Amul, battling it out in court. Ice cream-makers led by Hindustan Unilever, which sells the Kwality Wall’s brand, have accused the subsidiary of India’s biggest dairy cooperative of making it seem like milk is the only worthy ingredient.

In 2011, the Food Safety and Standards Authority of India decided that consumers should be told exactly what they’re eating on long summer days. That year, the FSSAI decreed that only products made with milk fat could be called ice cream; the rest, made with edible vegetable oil or palm oil, along with milk solids, had to be sold as “frozen desserts.”

Last month, Amul came out with an advertisement emphasising that it sells “real milk, real ice cream,” in contrast to other unnamed companies, which it said used cheaper and unhealthy vanaspati oil in their products. That sparked a row, prompting Hindustan Unilever, Vadilal, and other ice cream makers to take Amul’s parent company, the Gujarat Cooperative Milk Marketing Federation, to court, accusing it of tarnishing the image of their frozen desserts.

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“Amul has been airing a misleading television commercial since March 2017. This advertisement makes factually incorrect statements creating apprehensions among consumers of frozen desserts,” HUL said in a statement last month. In an e-mailed response to Quartz, the company declined to comment since the matter is under judicial consideration at the Bombay high court.

For the makers of frozen desserts, the stakes are really high, and time is running out.

Ice cream, you scream

As India’s peak summer selling season sets in, fast-moving consumer goods companies are gearing up for big business in cold beverages and ice creams.

India’s ice cream market is estimated to be worth over Rs 4,000 crore, and features 10,000 manufacturers that make everything from frozen mango bars to red velvet ice cream cones. Amul, one of the world’s largest milk processors, does brisk business with its kulfis and tricones, accounting for a massive 32% of the market. For the year ended March 31, the company recorded a turnover of Rs 27,085 crore.

No wonder then that the makers of frozen desserts are furious.

Typically, most ice cream makers use vegetable oil as a smoothening agent for their products, along with other milk solids. That helps reduce production costs because vegetable oil is cheaper than dairy fat. But the FSSAI’s 2011 decision suggested that products made with pure milk fat were richer and healthier than their oil-based counterparts. So, health-conscious consumers were more likely to look for what they thought was the real deal, i.e. milk-fat-based ice creams.

Amul’s advertisement, however, made things worse by bringing vanaspati into the mix.

Vanaspati is a refined oil that is considered to be unhealthy because of its high trans-fat content. But it’s also cheaper than other cooking oils, which helped make it a useful alternative in many Indian households.

Hindustan Unilever has argued that its frozen desserts do not use vanaspati oil.

“The advertisement makes incorrect claims about the usage of ‘vanaspati/vanaspati-tel‘ in frozen dessert products,” an Hindustan Unilever spokesperson told The Times of India. “We wish to clarify that Kwality Wall’s range of ‘frozen desserts’ do not contain vanaspati. In fact, Kwality Wall’s range of frozen desserts contains milk/milk solids like ice creams. The only difference is that frozen desserts use vegetable fat instead of dairy fat, which actually makes them healthier as they have lower saturated fat and do not have cholesterol.”

So far, however, Amul remains unmoved, saying it will not be intimidated by legal action and will continue to educate consumers about the benefits of its products. Amul did not respond to Quartz’s queries.

“To me, it’s not ‘frozen desserts’ that spells the difference, but the negative associations with vanaspati oil,” Kiran Khalap, co-founder and managing director of branding consultancy Chlorophyll, said. I would presume (the case) will help Amul positively.”

India’s ice cream war is heating up.

This article first appeared on Quartz.