The meaning of halal as per google is

adjective: halal

1. denoting or relating to meat prepared as prescribed by Muslim law. "halal butchers" religiously acceptable according to Muslim law. "halal banking"

noun: halal 1. halal meat.

Today there was a news article saying a certain coffee is now halal certified; NT News writes:

TERRITORIANS opposed to halal certification are boycotting Paul's Iced Coffee, flooding social media with their protests.

The iconic Territory drink has been the target of online hate because it is halal certified.

How can liquid/milk be certified as halal? There is no meat in milk or coffee, then what does halal certification mean?