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Comment by lowmemcpu | Hacker News Reader

> Habitual coffee consumption ranges from about 1 to more than 5 cups per day, which indicates that the daily dose is defined by something other than genetic reasons.

One curious question I've always struggled with is, what is a "true" cup of coffee? I've often seen people say a "coffee" cup is 6 oz, but then I'm confused by this:

1 US cup = 8 oz

1 Imperial (British) = 10 oz

1 Australian cup = 8.45 oz

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Brewed coffee varies so much in potency, I'm not even sure how much the quantity of the liquid even matters. A shot of coffee that has been cold brewed with finely ground beans for 48 hours is dramatically more potent than a giant cup of coffee brewed quickly with less-fine grounds and hot water.

From the Wikipedia article:

Caffeine is moderately soluble in water at room temperature (2 g/100 mL), but very soluble in boiling water (66 g/100 mL).

Caffeine is 33 times more soluble in hot water!

What matters more, then, is the concentration of coffee grounds to water, and how much of that water is left in the grounds.

> Caffeine is 33 times more soluble in hot water!

On the other hand, you "boil" your coffee for 2 minutes, not 2880 minutes (48h). But I'm no chemist, so you might still be right, despite the different orders of magnitude. Also, we're not factoring in the water/steam pressure.

Anybody volunteers for extracting coffee with an espresso machine for 48h?

This doesn't have to be academic. You can do an experiment at home. Brew a big cup of coffee with a drip machine and drink it. Note how you feel. Then, make a batch of cold brew and let it sit for 48 hours. Drink half as much of that as you did the hot brewed coffee, but pease do so slowly as some people become very uncomfortable with that amount of caffeine.

Yes, cold brewed coffee can have much more caffeine than you'd expect given the smoothness of the taste. Back when my brother managed a coffee shop, the first time I popped into his work and asked his recommendation, he didn't warn me of the caffeine content. I was well habituated to caffeine, but quickly drinking 12 or 16 oz. of cold-brewed coffee left me feeling a bit dizzy, to the point I hung around the shop for a bit to make sure I was fine to drive.

> Brew a big cup of coffee with a drip machine and drink it. Note how you feel. Then, make a batch of cold brew and let it sit for 48 hours.

Nah, too many variables.

What I'm getting at is: if you brew identical batches with identical methods, where the only variable is the temperature, which will have more caffeine in solution?

I'm willing to bet at about the 48hr mark it probably doesn't matter a whole lot, so I probably agree-ish with ya'll.

When I brew a pot of coffee, I fill it with water just past the line that represents 2x the number of cups I want.

If I expect to drink 2 cups of coffee, then I fill it just past the "4" line. If I'm making a pot for multiple people and want 4 cups, then I fill it just past the "8" line.

I think this is pretty normal. To the point where we don't even consciously think about it. In practice, a "cup of coffee" represents two cups as measured by the manufacturers. The manufacturers say that 6 oz is a cup, but a standard American coffee cup is 12 oz.

I don't know why we don't simply make those match up.

> I don't know why we don't simply make those match up.

There are already so many units called the "cup".

If we do anything along those lines, perhaps we instead define a new unit, the 'mug', that is equal to exactly two US coffee cups (12 US ounces, 1.5 US cups, 1.44 UK cups, 2.4 lungos, 0.75 Starbuckses) of coffee.

Related: https://xkcd.com/927/

“coffee cup” is a semi-standard unit just like the ones you listed are. And yes, it’s about 6 fluid ounces, and no, nobody in the real world means “i drank 6 fluid ounces of coffee” when they say “i had a cup of coffee”.

Overloading is fun!

Instead of measuring coffee you could measure caffeine content, but a lot of effects may be in non-caffeine ingredients. Still, it's a first step.

That's what led me down this path. Searching the internet for "how much caffeine is in a cup of coffee" leads to the question of "what is a cup?", "how did you brew it?", "what kind of grounds did you use?".

the real world is very nonlinear.

“total dissolved solids” is a more comprehensive measure of coffee strength for the entourage effects reason.

Well, there does exist this standard by the Specialty Coffee Association specifically intended as a reference for testing: https://sca.coffee/research/coffee-standards

It suggests that the 'cupping vessel' be "between 7 and 9 fluid ounces (207 ml to 266 ml), with a top diameter of between 3 and 3.5 inches (76 - 89 mm)"

Many commercial coffee makers use 5 ounces when calculating the number of cups they serve. Scroll down to the comparison chart and look at the carafe sizes:

https://www.bedbathandbeyond.com/store/product/ninja-reg-10-...

Measuring weight of the dry ground coffee describes the actual consumption better. The standard espresso quantity is 7 g of ground coffee per cup (25 ml).

I've been confused by this for a while as well. The answer seems to be there's not such thing as a "true" cup of coffee. It pretty much just means whatever the respondent considers a cup.

(In contrast to studies on alcohol consumption, where researchers have standardized units. And even on surveys will make sure to clarify with respondents so they get responses in normalized units.)

There's an ISO standard for how to brew tea for laboratory comparison:

https://en.wikipedia.org/wiki/ISO_3103

Also here are all the ISO standards for coffee:

https://www.iso.org/committee/47950/x/catalogue/p/1/u/0/w/0/...

They don't yet have any brewing standards but a lot of what they seem to do is by nose with green or roasted ground coffee.

And for that matter, how does the brewing method of coffee play into the health benefits? If I brew really strong coffee, do I get concentrated antioxidants and plant goodness? If I brew weak coffee and drink a lot of it over a longer period does that help my body's uptake of it?

Not that knowing these answers will really change my coffee drinking habits, as this seems like a ridiculous micro optimization, but it would be nice to know a bit more about the mechanism here.

Not to mention that processing and roasting also changes the bean and the resulting coffee brewed from it.

What’s even more confusing, I think, is that even if someone defines one cup as a specific volume, approximately how much of a specific kind of coffee grounds or a specific instant coffee have to go into it? There can also be huge variations in the proportion of water used for black coffee, for example.

I’m looking for some way to get the caffeine content of specific coffee types and brands, even if those are approximate.

I think the cup count is useful from the habit standpoint, but the study should probably also include style of coffee or caffeine content.

If I drink brewed coffee I’m on a steady flow for the day, sometimes making a second pot in the afternoon. I bought an espresso machine about a year ago, and one Americano in the morning pretty much sets me up for the whole day.

For me, I use 20g of coffee, ground to a 20 on a Baratza Virtuoso, with a 275mL of water in a French press, brewed with boiling water for 4 minutes.

If you change any of these variables- grind size, water temperature/volume, amount of coffee, etc, you drastically change the caffeine content.

The instructions I follow for my pourover requires 350 grams of water. Much more than 8oz. It drives me crazy, but it also tastes good! Though If I only poured until reaching the 8oz mark it's also quite nice. That said, there is a question of "full-extraction".

Usually the ratio is 1:16 for full extraction without bitterness @200f with grain size slightly larger than refined sugar. That’s to maximize taste, without regard for nutrients. The bitter compounds probably make no difference.

Glad I learned to drink coffee the italian way : one expresso cup (20/40ml). Strong, fruited, less caffeine. Loving it every morning.

In Europe, paper cups are usually 250ml (8.8oz) [1]. I presume German authors of this paper would have a similar volume in mind.

[1]: https://www.tingstad.com/se-en/foodservice/disposable-cups/p... as an example

It's already confusing enough before using another ambiguous unit.

1 us fl oz = 0.96076 * uk fl oz

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