Kulhad, Glass and Steel Each Change the Temperature Curve

What follows is the working version of how the serving vessel changes a cup of chai: the decisions in the order you actually meet them, with the reasoning attached.

Thin glass

A thin glass tumbler has very little thermal mass, so it takes almost no heat out of the drink when the tea is poured in. It then loses heat quickly through its walls, which is why a cutting glass moves from scalding to drinkable in under a minute. That fast curve sets a natural pace and means the tea is finished while it is still worth finishing.

Glass also shows the colour, which is how strength is judged at a stall and how a customer checks what they have been handed. The main disadvantage is that the glass itself becomes uncomfortably hot to hold for the first thirty seconds.

Unglazed clay

A kulhad or bhar is fired but unglazed, which leaves the clay porous enough to absorb a small amount of the liquid. That absorption is where the earthy, faintly mineral note comes from, and it is not reproducible in any sealed material. Clay has considerable thermal mass, so it takes heat out of the drink immediately and then holds it for a long time.

The net effect is a cup that starts cooler and stays warm longer, which is a completely different curve from glass. They are single use by design, which kept them cheap and also meant nobody ever had to wash one.

Stainless steel

Steel conducts heat extremely well, which means the outside of the cup reaches drinking temperature almost instantly. That makes a steel tumbler painful to hold and is why the traditional pairing is a tumbler with a wide-lipped bowl beneath it. Pouring between the two cools the drink rapidly and gives you something you can actually hold while it happens.

Steel adds no flavour of its own provided it is clean, which is an advantage over clay if you want the tea unaltered. It is also effectively unbreakable, which is why it dominates in households with children and in institutional settings.

Ceramic and porcelain

Thick ceramic has high thermal mass and low conductivity, so it steals heat on the first pour and then holds it stubbornly. That suits a large slow cup and works directly against a small one meant to be drunk in four minutes.

Pre-warming a ceramic mug with hot water removes the initial heat loss and is worth the ten seconds it takes. Glazed ceramic is neutral in flavour and easy to clean, which makes it the sensible default for a home mug.

It is the wrong vessel for anything served in a small measure, which is most of the chai worth drinking.

Size before material

Volume affects the temperature curve more than material does, since surface area rises more slowly than volume. A large mug of chai will always cool more slowly and stew more than a small glass of the same tea.

At the stall, that is why the last third of a big cup tastes different from the first, regardless of what the cup is made of. Choosing a hundred and twenty millilitre serving is a bigger decision than choosing between glass and steel. Two small servings from one pan beats one large serving on flavour every single time.

Leaf strength varies wildly by brand, so treat any spoon measure as a starting point.

Buying and keeping them

Toughened glass tumblers sold for tea are cheap, stack well and survive being poured into straight from a boiling pan. Ordinary drinking glasses can crack from thermal shock, so warm them first or buy ones rated for hot liquid. Kulhads are available from some Indian grocers and online, and they are genuinely worth trying at least once.

Ground fresh, steel tumblers last decades and are worth having simply as the most robust option in the cupboard. Whatever you use, keeping four of the same thing means a round of chai arrives at the same temperature for everyone.

The takeaway

Pick the vessel for the temperature curve you want, because the curve is most of the experience.

Measure it properly once, then never measure it again.