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Comment by Kirby64 | Hacker News Reader

The scientific definition of a 'cup' of coffee is important. Usually this is defined as 4 ounces of brewed coffee, which means a normal mug of coffee (which can fit something like 10 oz) would be 2.5 cups!

So, for most people's definition of a 'cup' of coffee, they really only mean 2.5 'mugs' of coffee.

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And surely the amount of water is inconsequential, why can't we just use grams of actual coffee? Then we don't have to worry about how many espressos are in a 10oz mug. (Nevermind what that person's considering a standard dose for the espresso!)

Measuring extraction ratio on coffee is difficult and wildly varies based on preparation method. The standard “cup” assumes 4oz of coffee, using 5oz of brew water (so, 1oz stays in the coffee grounds as waste). I believe there’s also a standard amount of coffee grounds used as well, though.

Different brew methods extract differing amounts from the coffee, so the amount of water is indeed consequential. Same grams of coffee in to a pour-over vs espresso would result in different amounts of extracted coffee material consumed.

True. I'm inclined to think it would be closer than 'do whatever you want in order to end up with an Xoz drink' though!

Prep method matters so much though. For comparison, a standard double shot of espresso is typically 18g of coffee. This would yield approximately 110mg of caffeine.

By comparison, the same 18g brewed using a pour over method should yield an 8oz cup of coffee with … likely around 170mg of caffeine.

Check out this James Hoffmann video specifically on this topic: https://youtube.com/watch?v=etnMr8oUSDo

I remember reading somewhere that the amount of caffeine in the cup is also proportional to the brewing time, therefore an espresso may not actually contain that much caffeine in the end (for the same initial amount of ground coffee, of course)

When I was in Organic Chemistry in College we demonstrated this experimentally. A cup of drip coffee had more caffeine than a shot of espresso. We were college kids so I'm not sure how consistent our how methodology was but the result was pretty consistent across all of us.

This survey is using self-assessed cups - without providing a cup size or any guidance. Specifically, a survey asks users "How many cups of coffee do you drink a day?" with no other context.

So, "cups" for this study is whatever the respondent considers a cup. For most people, that's going to be at least 8 ounces and probably 8-12 oz.

From the full text (https://ore.exeter.ac.uk/repository/bitstream/handle/10871/1...), here's how the intake is described:

> Habitual coffee intake was self-reported as cups per day, as part of the touchscreen questionnaire at baseline with the question “How many cups of coffee do you drink a day?” (38). Participants were asked to include decaffeinated (decaf) coffee intake in their response. Decaffeinated consumers were identified from response to the question “What type of coffee do you usually drink?”. Coffee consumption was grouped in seven categories, including non- drinkers, decaffeinated coffee drinkers, and caffeinated coffee drinkers consuming <1 cup/day, 1-2 cups/day, 3-4 cups/day, 5-6 cups/day and >6 cups/day. “Coffee drinkers” in the text refer to participants who report intake of caffeinated coffee. For sensitivity analyses we constructed separate indicators restricting the data to decaffeinated coffee drinkers and according to tea consumption, using intake categories as above"

True but I think the coffee machine definition of 4-5oz per coffee “cup” usually also assumes a stronger European strength of coffee which is quite concentrated. Most Americans seem to make coffee larger but more watered down, so it could be back to a 10oz mug is 1 or 1.5 cup equivalents.

Americans drink very watered coffee though compared to most of the rest of the world. For us that came from abroad, it is basically tea.

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