ELI5/How do water infusions such as cold brew go bad.

Question

ELI5/How do water infusions such as cold brew go bad.

In: Chemistry

Answer 1

Oxidation is a big one. Cold brew is water with a whole bunch of different little molecules floating around in it. A lot of those molecules react with oxygen over time to create a new molecule – one which tastes and smells different from the original one. This is why coffee grounds tend to be vacuum sealed.

Oxidation, like most chemical reactions, happens faster at higher temperatures, so hot coffee develops a stale taste faster than cold brew, but the reaction still happens even at fridge temperatures.

Additionally, cold brew coffee is water with a little bit of nutrients in it, which is exactly what bacteria and fungus need to grow. Leave it out long enough and a film of mold will appear on the top.