Question

why we should not keep sour stuff in metal utensils

Answer 1

Sour stuff are acids.

They do react with metals.

Acid + metals = salt+Hydrogen.

Hope this helps !

Answer 2

WE SHOULD NOT KEEP SOUR THINGS AS CURD BECAUSE IT CONTAIN ACIDS WHICH REACT WITH METAL AND FORM POISNOUS
COMPOUNDS WHICH CAN EFFECT OUR HEALTH