Normally we make buttermilk from scratch .We do not buy tetra packs for milk (off course some do...) but I have always bought milk in polythene packs (will take a photograph and add it later) and have to boil it every morning. When it cools its kept in the fridge and that's the normal practice in most homes here in Mumbai.
Some families like their milk to come directly from the dairy and you can either go to a dairy shop which gets these cans full of milk (buffalo -- full fat milk ) or you have someone delivering it to you right at your door step.
So, this cream which is formed over the boiled milk is collected in a separate vessel with a yoghurt starter used (a starter is a spoonful of curd which is put in the vessel to start adding the cream over it ) , leave it out for about 2-3 hours and then keep it in the fridge or you get very sour buttermilk after churning.
Go on adding your cream everyday I store it depending on my need , if I feel the need for buttermilk in two days I churn this mixture in 2 days but that gives me very little butter milk so I prefer to keep mine for around a week .
. If i have extra milk at the end of the day instead of heating and using it the next day i prefer to pour it in this vessel with the yogurt.
Then on the day I want to make the buttermilk I remove it from the fridge and leave it out for about 4-5 hours before I churn the mixture, this helps me to churn and get a fresh bowl of butter and buttermilk within a matter of minutes about 10 mins.
I churn the mixer with a wooden churner with my hands you can use a blender too but i prefer this old method which makes me feel back to my roots .
The end product of this churning is a soft , melting ball of homemade white butter and a glass full of yummy and fresh buttermilk.
I use this buttermilk for
Eating rice with buttermilk (plain) its yummy with a little hot mango pickle.
Eating rice with spiced buttermilk
Making buttermilk dosa's
I normally give my maids a glass full of buttermilk to drink when i have it fresh .