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Comment by cout | Hacker News Reader

As I understand, the serving temperature of coffee does have an effect on perceived acidity (which is NOT the same as pH), though I don't understand the science behind it. Here is one paper that claims it is due to release of volatiles at higher temperatures: https://www.sciencedirect.com/science/article/abs/pii/S03088...

If that's correct, then warming the coffee again to that temperature would again speed up the release of volatile compounds, though what effect that might have on flavor is anyone's guess.

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I could buy it, that it might have some perceived effect that’s measurable. I have tasted many a warmed up cold brew, and it tastes like coffee to me. The ones that are actually cold brewed are milder, and the hot brewed fakes are noticeably sharper, and I feel it later in my throat… The thing for me is that the actual acidity of coffee has started causing some inflammation. The reason I’m seeking cold brew is my doctor recommended it. I’m less worried about the perception of acidity and more worried about issues caused by too low pH.

Cold brew isn’t about pH, it’s about bitters. The oils aren’t (just) acidic, they’re bitter, and that’s what you don’t get when you make real cold brew instead of failing it.

Acetic acid is sour. Alkaloids are bitter.

As a complete layman, when I tried tossing cold brew into the microwave it ended up tasting pretty gross. Like, jarringly so.

I won't pretend to know the science behind it, or perhaps I warmed it differently than what the parent poster does, but I definitely sympathize with the barista's hesitation in his story.

Yeah, there are still a lot of dissolved coffee solids in cold brew that get further extracted if heated. There are also a lot of volatile compounds that break down when heated. The idea that you can just reheat coffee, even cold brew and have it taste the same is just ridiculous.

Also, in my experience heating the coffee in microwave increase perceived acidity even more. Which kind of make sense with this explaination as there could be pockets of superheated water when it is microwaved.

Could you try giving it a good stir right before putting it in the microwave?

Just curious, why do you think that would help?

Not the poster you're asking but they might have imagined the stirring being vigorous enough to keep the liquid moving during the entire heating period.

Ah, just posted that I detect a change in flavor after I heat cold brew (but didn't know a mechanism behind it)!

Isn’t that a pretty generic and well known (and not coffee-specific) effect, that flavor is pretty temperature dependent?

Warm Coke is disgusting; freezing cold Diet Coke is the nectar of gods.

room temp soda is my favorite. there's so much more flavor when it's not cold.

however HOT cola (which can happen if you leave it in a car) is physically painful because something weird happens to the bubbles

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