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All your questions about milk answered

Do you need to boil milk to make dahi, paneer or coffee? And what is the deal with lactose intolerance?

Illustration by Krish Ashok. 
Illustration by Krish Ashok. 

The literature of Vedic times is replete with references to the critical importance of what is essentially nutrient-dense liquid food produced by the mammary glands of domesticated, non-consensually impregnated ruminant mammals such as the cow, buffalo, sheep, goat and camel. The magnificent bull and cattle seals of the even earlier Indus Valley civilisation are indirect evidence of dairying and animal husbandry in the subcontinent over 5,000 years. These animals evolved around 30 million years ago when the earth went through a seasonal arid period, one that caused the expansion of grasslands and the extinction of herbivores that could not eat and digest dry grass. Ruminants, with their specialised multi-chambered stomachs, could digest this fibre-heavy source of food and turn it into milk (and meat). This also offered early agricultural societies a mechanism to use up what is otherwise useless post-harvest plant fibre produced by grain-bearing grasses like rice and wheat.

Early human societies that managed to produce milk from ruminants ended up with an evolutionary advantage as it offered a replacement for human breast milk for a growing child. Prior to the rise of dairying, most adult humans did not possess the ability to digest lactose, the primary carbohydrate present in milk. But early societies that started consuming cow or buffalo milk after weaning developed varying degrees of tolerance to lactose. A contemporary world map of lactose intolerance is also a map of where dairying was more central to nutrition historically—typically, northern latitudes.

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Even in the subcontinent, it is estimated that about 70% of adults in north India can tolerate lactose, while only 30% of south Indians can. This explains the centrality of milk and milk products to the cuisines of north India in comparison to the south. East Asians, for instance, have very low lactose tolerance, which is why when you order tea with milk in that part of the world, soy-milk (the only plant source of milk that is nutritionally complete by itself) is the default, not dairy milk.

Cow’s milk is 88% water, and the rest is fat, protein, carbohydrates and minerals. Buffalo’s milk is higher in fat content and is often preferred when making creamier milk products. Modern-day industrial dairies in India tend to collect milk from multiple individuals who own dairy animals and then homogenise and pasteurise it to produce a product with consistent nutritional content. On its own, milk straight from the animal will have mammary gland cells, enzymes and lots of bacteria, all of which add to the flavour but tend to reduce milk’s shelf life to a few hours at best.

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Let’s start with how you boil milk—and whether you need to boil pasteurised milk. If you are boiling milk to feed a toddler, you may not want to take any risks. Pasteurisation kills most, not all, bacteria; UHT (ultra high temperature) pasteurisation kills almost every living thing in the milk. If you are heating milk for coffee, then you should avoid any temperature above 62 degrees Celsius, for the casein proteins will denature and milk will lose its creamy mouthfeel. If you are preparing milk to make yogurt, you need to bring it to a vigorous boil, just short of spilling, to make sure you have completely denatured all the casein protein, so that when you introduce your friendly lactobacterial culture (aka yesterday’s dahi), it can produce a single, solid curd structure.

Making cottage cheese requires a medium level of heat and the introduction of acids like lime juice or vinegar. Acids curdle milk and separate the casein protein from the whey (the thin, watery bit) and this can then be further dehydrated using a muslin cloth and gravity to produce paneer. The use of enzymes like rennet (historically produced inside the stomachs of ruminant calves but nowadays also produced from fungi) instead of acids results in more complex-flavoured cheeses like Cheddar and Gouda.

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Full-fat, unhomogenised milk can also be whisked (or simply rested for several hours) to render out butter fat, which can then be used as is or clarified using heat into ghee. The distinctive flavour of ghee and butter are a function of the diet of the cows involved. A diet of poorer quality, dry hay results in milk that has a more neutral, cheesy flavour in comparison to the fruity notes from milk produced by cows that have had fresher pasture to graze on.

The use of milk instead of water in any kind of wheat dough lends a softer and flakier texture and the milk proteins also react with the starches in the dough at high temperatures to cause browning reactions that result in more flavour.

No place on the planet does more with milk than India. The veritable cornucopia of milk-based desserts, made by heating milk repeatedly to reduce its moisture content and then using acids to create a fluffy final product, includes the entire universe of sweets from rasmalai to gulab jamun.

As Ogden Nash put it rather profoundly: “The cow is of the bovine ilk; one end is moo, the other end milk.”

 

Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok
Illustration by Krish Ashok

Krish Ashok is the author of Masala Lab: The Science Of Indian Cooking.

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