You take about a kilo of black, but not rotten, bananas, peel them and chop into short bits. cover with water and boil for about 15 minutes. the banana pieces should still be whole and not falling apart. then you strain and cool the liquid. Add the liquid (or 'gravy') to wine at any time but I added it to mine last and left in a cool place to clear. took a week. Crystal clear!!! also adds body to a slightly thin wine.