Dairy is central to Indian cooking across the country, but the forms it takes differ sharply between north and south. The divergence tracks climate, cattle and what could be kept.
Heat determined what fresh milk could become
Before refrigeration, fresh milk in a hot climate had a window of hours. Anything that could not be used immediately had to be transformed into something stable.
Souring is the fastest transformation available, so southern dairy centers on cultured products: set curd, buttermilk and the fats derived from them.
Cooler northern winters gave more room for fresh milk preparations, which is where the long reductions and fresh cheeses that define northern sweets became practical.
Reduction is a northern investment of fuel and time
Cooking milk down for hours consumes fuel and requires someone at the stove, and it produces a concentrated product that keeps far better than the milk it came from.
That trade made sense where dairy was abundant and where the resulting solids fed a large sweet-making trade centered on shops rather than homes.
The northern sweet repertoire consequently leans on reduced milk and fresh cheese, both of which need a steady supply and a place to process it.
The south built its dairy around ghee and culture
Ghee stores at ambient temperature indefinitely, which made it the sensible endpoint for surplus milk fat in a hot climate.
Southern sweets therefore use ghee heavily as the cooking medium and flavor carrier, with legume flours, rice, coconut and jaggery providing the body that reduced milk provides further north.
Buttermilk drinks and curd-based dishes carry the fresh dairy portion of the diet, occupying the role that milk-based preparations take elsewhere.
Cattle and land shaped the supply
The northern plains supported large-scale dairying with the fodder to sustain it, giving a milk surplus that could be spent on labor-intensive processing.
In much of the south, coconut and rice were the abundant local resources, and dairy was a supporting ingredient rather than the structural one.
That is visible in the sweets: coconut and rice appear where reduced milk would in the north, doing the same textural job with a different raw material.
The two traditions have mixed but not merged
Refrigeration and transport have made every form of dairy available everywhere, and shops in both regions now sell sweets from the other.
What has not changed is which sweets a household actually makes, since the home repertoire follows the technique people learned rather than what is on sale.
For a cook in the United States that distinction is useful, because it indicates which recipes assume long stove time and which assume a jar of ghee and a bag of flour.