Brass is copper and zinc. Both are fine metals for conducting heat and both will react with acids: tomato, tamarind, citrus, vinegar. Leave a tamarind curry in unlined brass overnight and the surface tells you about it by morning.
The traditional answer is not a different metal but a lining. Tin does not react with food the way the underlying alloy can, so a lined vessel handles everything an Indian kitchen throws at it, from tomato-heavy gravies to buttermilk Kadhi.
This is why we say every one of our pieces is kalai-lined without hesitation. Selling unlined peetal as everyday cookware would be selling a problem. The lining is not an upsell or a feature; it is the minimum standard for honest cookware.
One consequence worth knowing: the lining wears. It is softer than the metal under it and it thins with decades of stirring. A vessel that needs a re-tin after some years is not defective. It is working exactly as designed, and renewal costs care, not a new pot.
Side-by-side of unlined brass rim and tin-lined interior of the same vessel.