I use a cheap Mr Coffee to heat my water for my AP if I'm making multi cups during the morning. Plenty of water at the aprox. temp they say is right for brewing. Extra hot water is great for rinsing the AP when finished. Quick, simple, drinkable and I don't need to make a full pot at work. I'm tired of buying coffee for everyone or throwing 1/2 of it away. Most at my work wouldn't know good coffee if they drowned in it anyway...
Posted Sat Apr 14, 2012, 9:05am Subject: Re: Aeropress is nice but...
jpender Said:
You just multiplied by the density instead of divided. I made the exact same mistake (twice in a row) the other day.
According to Illy, "typical" espresso is 1.02 g/ml with 53 mg/ml solids. That implies a coffee solids density of 1.6 g/ml (or 0.62 ml/g). I'm not sure if that includes the lipids.
What I thought to do was add coffee grounds to water topped up to a precise volume. Then the weight would give me the density of the solids. But when I tried this with cold water there were all of these little tiny bubbles in the mixture that were very persistent. It looked like a flask of Guinness. With all that extra gas and the buoyed up grounds and foam what I initially came up with was 0.8 g/ml. Then after stirring and waiting half an hour it was 1.0 g/ml. Another half an hour and it settled at around 1.3 g/ml.
I tried it again using hot water. After the water cooled there was no gas and very little crud on top. I topped up the flask and got about 1.4 g/ml (0.74 ± .05 ml/g).
But I was wondering how different are the densities of the soluble and insoluble fractions? And might there be a significant volume contraction when the coffee dissolves? Those tiny gas bubbles sure displaced a lot of water.
I was kind of hoping it was something you'd explored.
Just was playing around with some Tanzania this morning.
A quick check on my "typical" pour with some small bloom total brew mass is a few mm below the top of the cylinder (clear aeropress) which has a typical cold water fill volume of 280g is around 260g (coffee+brew water, measured right before cap fitting, reverting and pressing).
One cup I did a 1 minute cool water pre-soak with 23g of water and 23g of coffee. Then, I poured to start the extraction, topping right to the rim with about 1mm of bloom over the top. 90% of the grounds were submerged in 30 seconds, then I topped off a couple of mm that subsided as the bloom went away. At the end, the total brew mass was 281.2g. Afterward, I did a 2nd check of the volume at my normal inverted setting and got 279.5g of cold water.
Afterward, I checked the approximate volume of the puck left behind - around 25mm tall X 57mm diameter moderately compressed, weighing about 52g. Interestingly, the height of the puck increased as it evaporated over the next half hour (and as I enjoyed a darn near cup of perfection!).
So Illy says that espresso total density is higher than water? At what temperature?
Water is max density at 39°F, lower than that temp to ice, it goes lower (in g/ml). Higher than that temperature and the density goes lower (in g/ml). 1.03 is the specific VOLUME (ml/g).
Your approximation is fine, though, for calculating volume - I always default to density in my head, and just divide where necessary.
My calcs for the cupping example are all by mass measurement - the only volumetric measurement that is meaningful is when the cup is filled to the brim (in my case 180ml).
10g of coffee, +160g of water is 170g of coffee brew mass. When the bloom subsides and after breaking the crust, this 170g of brew mass occupies something less than 180ml (because it is no longer at the rim).
After a half hour undisturbed, there is no floating grounds, nothing on the top except some oil, no foam. The temperature is now down to about room temperature (in my case about 25°C or so). It also now weighs only 160g. It takes 30ml of cold water to top the cupping mixture up to the brim (180ml) so by subtraction the total volume occupied by the cooled brew mass is 150ml.
At the beginning, 170g of brew mass divided by 180g of volume = 0.94 density. A chunk of this is bloom, obviously, since I'm measuring "volume" by how much I can fill a cup. The grounds are floating (much of them anyways), because they haven't absorbed any water. The water at this point is only 0.96-0.97 g/ml.
After 5 minutes, stirring (with a very small metal stirrer - actually my thermocouple - so I don't pull out much liquid) it weighs about 168g but now occupies less volume (estimate about 165-170ml). New density: 168g/170ml(ish) is right around 0.99 to 1.00.
At the end, 160g of brew mass, occupies 150ml of volume = 1.06 g/cc. Some of this is due to water evaporation. Some of this is due to cooling of the liquid (water is about 3-4% less dense at near-boiling).
I did go ahead and filter a sister brew that duplicated the masses within a tenth or two gram, then dehydrated them. That's in another spreadsheet on disc - I'll have to dig them out (decommissioning an old desktop, transferring files to new computer, etc.), but I recall being surprised that the extraction wasn't way over the top overextracted.
I also was playing around with my new 500X0.01g AW scale - 10ml of cool water weighs (according to my scale) 9.97g. 10ml of cool coffee, filtered, weighs about 9.79g. <shrug> Right now that means that brewed coffee at 1.17% strength is close enough to water density for me, for now. I'll repeat this when I get some new 60ml syringes.
jpender Said:
I'll bet you have a fat notebook filled with interesting observations about coffee.
More like plural... ROFLOL! And prolly hundreds of megs of spreadsheets and electronic notes, too. ;^D
Your original formula is a bit off to me, it implies that coffee grounds are MUCH denser than water (you use 0.75ml/g implication that the specific density is 1.5g/ml).
I figure the interstitial water in the grounds gets the specific density more like 0.9g/ml on initial pour, and hot water at 0.965g/ml.
(240g÷0.965g/ml) + (45g÷0.9g/ml) = (248ml) + (50 ml) = 298ml estimate (close to the max extended length of the Aeropress in my double cup recipe with suppressed bloom), or approximately 0.95 - 0.96 g/ml for the entire brew mass. As the brew settles down, you can see the volume decrease even over the course of a few minutes.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
My calcs for the cupping example are all by mass measurement - the only volumetric measurement that is meaningful is when the cup is filled to the brim (in my case 180ml).
I was just pointing out that you'd have a reading error due to the diameter of the cup (1 mm height equals 3-5 ml?) when trying to decide exactly when it is "full", especially with bloom and floating grounds. This would make density measurements challenging.
Netphilosopher Said:
I also was playing around with my new 500X0.01g AW scale
Did you get the LB-501? I've been shopping for another scale and would love to hear what you think of yours.
Netphilosopher Said:
- 10ml of cool water weighs (according to my scale) 9.97g. 10ml of cool coffee, filtered, weighs about 9.79g. <shrug> Right now that means that brewed coffee at 1.17% strength is close enough to water density for me, for now. I'll repeat this when I get some new 60ml syringes.
jpender Senior Member Joined: 11 Jul 2011 Posts: 394 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Sat Apr 14, 2012, 3:49pm Subject: Re: Aeropress is nice but...
Netphilosopher Said:
Your original formula is a bit off to me, it implies that coffee grounds are MUCH denser than water (you use 0.75ml/g implication that the specific density is 1.5g/ml).
There were 34.5 g of grounds in 749.5 ml of water for a total volume of 775 ml. No air, no foam. How would you interpret that?
Netphilosopher Said:
I figure the interstitial water in the grounds gets the specific density more like 0.9g/ml on initial pour, and hot water at 0.965g/ml.
(240g÷0.965g/ml) + (45g÷0.9g/ml) = (248ml) + (50 ml) = 298ml estimate (close to the max extended length of the Aeropress in my double cup recipe with suppressed bloom), or approximately 0.95 - 0.96 g/ml for the entire brew mass. As the brew settles down, you can see the volume decrease even over the course of a few minutes.
Well... I had to try this. I used 18g of coffee and pre-infused with 18g of 50°C water, then another 213g of 96°C water to top up the Aeropress. I had the plunger set so that the max volume was 264 ml. The initial "brew mass" density was 0.9 g/ml and the calculated grounds density was 0.7 g/ml. But this included a 1 cm thick plug of foamy grounds on the surface. If just half of that plug were air the non-air volume would be about 12 ml less resulting in a calculated grounds density of about 1.5 g/ml.
After about 20 minutes I topped up the level with water, reweighed, and checked the temperature. Both the brew mass and the grounds had a density of 1.0 g/ml. There was still a fairly thick plug of foam on top.
About 25 minutes after that I topped it up again. Now the foam was almost entirely dissipated. The brew mass density was still 1.0 g/ml but the grounds density calculated to 1.6 g/ml.
This was the same progression that I observed in that large flask of cold water and coffee. In that case there was very little foam but there were tiny suspended bubbles that persisted for a long time.
Of course one might choose to include the volume of gas or foam, depending on objectives.
JP, I ended up getting the SM-501. Silver version was only $20 (weird, I had to re-find the silver version, which was inexplicably $30 cheaper than the blue or black ones Click Here (www.amazon.com) )
I was tossed up between the SC-501 (which appears to look exactly like my SC-2KG) and the SM-501. In all of my searching, I never found the LB-501, it would have been on the short list.
So far, seems decent. There's a stability function that isn't on my SM (a little "s" appears once the reading is considered stable). My 200g check weight plug popped out and I lost the inserts, so had to order some other reference weights - for now I actually use my cup to check (since I've measured it hundreds of times, lol). Only problem is it's over 500g.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
749.5ml of water, what was the mass of the water? Or did you add by volume, and if so at what temperature?
At what temperature is the 775ml taken, also at what time? It makes a difference (3-4% error in the volume of the water/coffee). Also, it may make a difference depending on when during the brewing you take the total brew volume.
I did get an email this weekend that mentioned things changes as the extraction completes - yes, the coffee (beverage/liquid) gets more dense due to cooling, but the mass leftover (as the emailer has pointed out I've proved many times) of the grounds is a lot less - about 20% less - than the beginning. It sure gives me pause.
I was trying to come up with an equation to predict brew volume so I wouldn't overflow. I use bloom suppression to eliminate the primary variable - excessive bloom - that displaces significant volume.
At the end of the brewing/extraction, though, the "mass" of the grounds is about 20% less.
At the beginning the equation that has worked for me is:
(brew water ÷ 0.965) + (coffee grounds ÷ 0.9) = estimated brew volume. This seems to predict (for me, YMMV) the stabilized brew volume at bloom dissipation and subsiding grounds during an immersion brew.
At the end of the extraction, but prior to separation the brew mass is still a solution of:
(coffee solution mass [brew water mass, minus evaporation, plus dissolved coffee solids] ÷ [similar density to water]) + (spent grounds ÷ spent grounds density) = slightly less than brew volume (based on observation).
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Well... I had to try this. I used 18g of coffee and pre-infused with 18g of 50°C water, then another 213g of 96°C water to top up the Aeropress. I had the plunger set so that the max volume was 264 ml. The initial "brew mass" density was 0.9 g/ml and the calculated grounds density was 0.7 g/ml. But this included a 1 cm thick plug of foamy grounds on the surface. If just half of that plug were air the non-air volume would be about 12 ml less resulting in a calculated grounds density of about 1.5 g/ml.
After about 20 minutes I topped up the level with water, reweighed, and checked the temperature. Both the brew mass and the grounds had a density of 1.0 g/ml. There was still a fairly thick plug of foam on top.
About 25 minutes after that I topped it up again. Now the foam was almost entirely dissipated. The brew mass density was still 1.0 g/ml but the grounds density calculated to 1.6 g/ml.
This was the same progression that I observed in that large flask of cold water and coffee. In that case there was very little foam but there were tiny suspended bubbles that persisted for a long time.
Of course one might choose to include the volume of gas or foam, depending on objectives.
I'm a bit confused: let me restate and see if this makes sense:
Topped volume set to 264ml on your AP.
You presoaked 18g of coffee with 18g of water, and then added water to the top of your 164ml, right? To do that, you added another 213g of water. Your observation at this point included 10mm (25ml) of foamy grounds (which I'll point out is MUCH less than some blooms I've measured at nearly 80% of the brew volume... this is very typical of fresh coffee with pre-soaking).
((213g+18g) ÷ 0.97) + (18g ÷ ? ) = 264 (including foamy grounds and bloom). I plugged in 0.97 for water density just because of 18g of 50°C water instead of 0.965. Grounds portion of the density is what you said, around 0.7 INCLUDING the bloom/floating grounds.
You didn't note the temp and total brew mass at 20 and 25 minutes, and the amounts you topped with (which tells you the volume change as the system cools). There's several things going on here, one of which is the ongoing extraction. At 20 minutes, it looks more like:
(231g - ? evaporation + (18*.2)) ÷ (approx 1) + (18*.8 ÷ ?) = maybe 250ml (depends on what you added to top off)?
I'll have to try a cold mixture to see if it makes sense - but there's a difference between the grounds density when starting and at the end of extraction. Bottom line is that counting the grounds density as heavier than water will cause you to exceed your brew device if you're running on the edge of capacity if you're using it to determine expected brew volume.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
... After about 20 minutes I topped up the level with water, reweighed, and checked the temperature. Both the brew mass and the grounds had a density of 1.0 g/ml. There was still a fairly thick plug of foam on top.
About 25 minutes after that I topped it up again. Now the foam was almost entirely dissipated. The brew mass density was still 1.0 g/ml but the grounds density calculated to 1.6 g/ml. ...
Sorry, jp, just thinking about this again over lunch.
You mention the brew mass density at 20 and 25 minutes being 1.0g/ml after you re-topped the system off (to 264ml) - so this implies that your added water made the total mass ~264g.
At any step of the system, the solution can be modeled as a closed form:
(solution ÷ density) + (solids ÷ density) = volume. It also has a total brew mass at any given point.
Initially, hot, it looks something like:
231g @ 0.97 + 18 @ 0.7 = 264ml, with a total brew mass of 249g. Unless I'm missing something, the brew mass density is 0.94. (this includes the foamy floating grounds).
After 20 minutes, the extraction is pretty much done. According to my VSTcr, best case scenario in the AP is about 21% extraction, but we'll round it off to 20%:
You mentioned that after you topped it off, the density is now 1.0, meaning there was some contraction and/or evaporation, but the total brew mass by inference is now 264g. However, the grounds now have only 80% of their original mass (the other 20% is now in solution):
Total brew mass = 264 Approx undissolved coffee mass = 18*.8 = 14.4g Remaining coffee mass by inference must be 249.6, so it now looks like:
Remember, this is only a valid calculation of the grounds density when it has interstitial water. I made an error in my last calculation of the puck density - and why I was surprised when I had close to 1 (when I was expecting 0.7-0.8) - once I get as much of the water out as I could, I forgot that the puck only contains a portion of the original mass of the coffee. Just like the difference between the density of dry packed sand (with interstitial air), wet packed sand (with some interstitial water), and the calculated density of sand in water if the water is known (fully submerged sand) , vs. fused silica solid or silicon dioxide (basically solid "sand" for all practical purposes).
The 25 minutes you stated you topped it off again, but the density stayed 1.0g/ml. Either you exactly replaced whatever evaporated (masswise) in the last 5 minutes, or the measurement of the mass is varying by a few grams. Either way, and even if you count the amount of original grounds or spent grounds, the density of the grounds is hovering a bit more than 1.0:
If you assume the grounds are the original mass of 18g: 246 @ 0.998 + 18 @ 1.025 = 264ml (and total mass = 264g to make the overall brew mass density = 1.0)
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
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