Actually a burp tax. Cows release 80% or more of their methane via the mouth. The gas is generated in the last three chambers of the rumen the cows multi chambered stomach. There is little to no gas created in the intestines of the cow. Unlike monogastric animals that have acidic stomachs and anaerobic intestines such as pigs or humans. By the time the digestate leaves the rumen it’s primarily acetic acid, and bacteria proteins which what the cows actually “eats” it’s symbiotic relationship with it’s rumen microfauna has converted cellulose/hemicellulose to acetic acid, some remaining glucose and pentose plus all this a wonderful bacteria that make that possible. Yes as a matter of fact I am a scientist.
You are right the editors of this story called it a “fart tax” in the headline then amended it to say “burp and fart tax”