Trying to understand what’s causing this. A little context , i get morning cappuccino with oat milk every day at Blue Bottle , it’s amazing , but recently for around 4 weeks, i noticed the foam after coffee stays for like a few minutes the rainbow iridescent bubbles start forming. I switched the blend and milk from oat milk to brevet option milk, one day it didn’t do that, the next day which is today same thing. Any ideas what’s that ? I didn’t find much online , baristas seems to not know what’s causing this , Blue Bottle support gives very vague answers
by redfencer
3 Comments
My first thought is that there was soap left in the frothing pitcher or wand that caused this. Second thought is most oat milks have emulsifiers added like sunflower oil and that oil film mixed with water from the steam wand is causing it [Thin Film Interference](https://en.wikipedia.org/wiki/Thin-film_interference
it’s because it’s pride month
coffee has oil in it, that’s why people need to clean their grinders or they can get rancid