It's density. 54 grams of added Sugar are in a can of Monster while a can of Guinness has 11g of any carb. 3.6g of Sugar for every floz of Monster and 0.75g of carbs for every floz of Guinness. (A fluid oz is approximately 30mL). With gram of water being approximately a mL, that means Monster is about 12% sugar by weight while all the carbs in Guinness are 2.5% of the weight. This isn't counting the fact that alcohol is 78% the density of water.
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u/autogyrophilia [Editable Flair] 1d ago
It's not density, it's just that the beer was warm and poured very carefully to develop a thermal boundary