Under what theory is coffee and water weight related?

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bobroseman
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#1: Post by bobroseman »

Under what theory is the weight of ground coffee related to the weight of water passing through it? I admit to being out of touch with brewing theory for the past ten years and my last chemistry course was completed in middle of the last century. Even though I don't understand I willingly embrace the theory that one should weigh the espresso rather than measure the volume as I have done for the last decade (alas for all of the goodness I have wasted). I have even invested in a scale.

Yet....yet... I can't wrap my head around the theory. Why is the weight of water relevant? And if it is shouldn't I fill my Technivorm with a pound of water next time I want a cup?
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[creative nickname]
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#2: Post by [creative nickname] »

With water, volume and weight are linearly correlated. So a liter of water is always a kilogram. With espresso, this is no longer the case, because crema amplifies volume in an unpredictable way relative to the mass of water used. But the mass of water going in is what effects the extraction level of the coffee, so that's why you care more about the weight than the resulting volume.
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Sideshow
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#3: Post by Sideshow »

And it's the weight (mass really) of the resulting beverage that's the key, not necessarily the weight of the water passing through, although they will obviously be very closely related.

bobroseman (original poster)
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#4: Post by bobroseman (original poster) »

Then is double the coffee weight arbitrary based on taste? The weight of one fluid ounce of water is about 28.4 g. Brewed coffee has some solids and crema in it so a two fluid oz double won't be 56.8 grams. But why 36 grams for 18 grams of coffee? Why not 45 grams? Why not a different weight at different temperatures or as the coffee ages?

Walk me through how you guys pull a shot first thing in the morning. How does the pro barista dial in every hour?
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pj.walczak
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#5: Post by pj.walczak »

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Pawel

bobroseman (original poster)
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#6: Post by bobroseman (original poster) replying to pj.walczak »

Very good exposition of what I suspected. I am off to try 3:1.

Thanks
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Sideshow
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#7: Post by Sideshow »

bobroseman wrote:Then is double the coffee weight arbitrary based on taste? . . . But why 36 grams for 18 grams of coffee? Why not 45 grams? Why not a different weight at different temperatures or as the coffee?
In a sense it's arbitrary, but the same way that anything based on taste is arbitrary (why is a tablespoon a tablespoon and not a few small weight or volume units bigger or smaller). The community settled on the definitions of basic categories of shots because these categories tend to be meaningful to the people who pull shots. Ristretto ratio is 1:1; normale ratio is 1:2; lungo ratio is 1:3; and Americano is 1:>3. These are just general guides to frame your approach. Greater ratios have different characteristics than smaller ratios. Ultimately do what pleases you most based on your experimentations.

My shots tend to range from 1:1.5 to 1:2 depending on my preparation and the coffee. It also sometimes depends on if I'm making a milk drink or drinking espresso only.

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Marcelnl
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#8: Post by Marcelnl »

I tend to end up with a 1:1 to 1:1.5 ratio just based on my taste preference, I aim for the taste I like in a new coffee and then check the ratio not the other way around. Over time I learned that the lower ratios are more to my liking, when pulling shots for friends I go slightly longer as most find what I like too strong.

For me the ratio is a way to communicate the sort of end result in an easier way then trying to describe the taste profile.
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samuellaw178
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#9: Post by samuellaw178 »

The old recommendation around the forum was to cut the flow when it blonds. Most often than not, that happen to be around 1:2 brew ratio (for me and my setup). It's only recently people are moving onto more 'scientific' and more accurate measurements (it's for the good I agree) by sticking to a gravimetric brew ratio. But some of the subtleties got lost in the movement. This is especially true when we are pulling lighter harder-to-extract coffee yet still sticking to the same brew ratio. I agree with above the better way is to pull the coffee and taste, then check the brew ratio for replication.

I tried coarsening my grind slightly and increasing the brew ratio this morning (and did the grinding into a separate container thing recommended in the comment section)..still preferred the 1:2.x ratio than 1:3 (which I had verified before). I get slightly higher calculated extraction yield with 1:3 ratio (21.6% EY vs 20.5%, might be within measurement error) but tastewise the 1:2-2.2 was preferred and that's what I'm sticking to. But my setup (water,coffee,machine,grinder,preference) is different and so does everyone else's.

Keep in mind Rao isn't recommending a specific fixed ratio (no one ever did but somehow the 1:2 ratio just caught on). The blog post was to urge people to experiment as more often than not, the coffee (presumably lighter roasted coffee prevalent in his circle, context is equally importnat) are underextracted by sticking to a fixed recipe.

bobroseman (original poster)
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#10: Post by bobroseman (original poster) »

Thanks for the info. Makes sense now.
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