Critical point of butter: its halal status
Principally, how to make butter in the past until now is similar. The difference is only in its original material. If in the past it used fresh milk, while now it uses cream (milk if separated by a cream separator will produce a rich cream and skim, a solution which contains protein). The main ingredient of butter is cream with fat content between 25-45%.
The problem of its halal status is when preparation of the butter involves fermentation. It is doubt because the growing medium of lactic acid bacteria is suspected of its halal status, and the media itself can be mixed into the butter. If the butter is made without fermentation, the halal status is not problematic, unless it is added carotene as colouring agent because carotene usually is in a carrier (coating). One of the ingredients that can be used as a carrier is gelatine (can be made from pig, cow or fish).
In conclusion, after finding out how butter is made, we must be careful with the butter product that has strong smell (made by fermentation) due to its doubtful status. Choose butter who has examined its halal status (which has halal label).