AnotherSadDrip Senior Member Joined: 6 Feb 2013 Posts: 3 Location: KS Expertise: I like coffee
Posted Wed Feb 6, 2013, 8:12pm Subject: Water temperature, density, and mass
I have been struggling with the issue of water density for a couple of days now. I use a #6 filter cone and filter with a ratio of 66 g/liter--usually using either 33 g or 66 g of coffee depending on how large of a batch I am making. If I am understanding correctly, water has a lower density at higher temperatures. If I pour 1000 g of water at approximately 200* F, am I actually pouring less than 1000 ml? If so, is the difference negligible, or should I pour, say, 1004 g instead?
Fair enough—taste is everything! As to your second point, I do weigh both coffee and water in grams, and it wasn't until I was reading about the SCAA's 60g/liter recommendation that I ever even thought about volume. (I keep getting hung up on this idea that the weight of 1 liter of water is going to differ at different temperatures. Honestly, I've just been a bit bothered by not being able to wrap my head around what seems like it ought to be a fairly simple math problem.) I am going to back to my old ways, as you suggest.
Well, it is a guideline rather than a rigid rule. If you were to brew at 75°C then a liter would be 975g and at 100°C that liter would be 958g for roughly 1.7% change in mass (of course it would be much less of a change from 90°C to 95°C, my usual brewing range).
Personally, I brew around 50 to 55 g/liter in my presspot at work because that ratio usually tastes good to me. I do weigh grounds and water, but when I consider other uncontrollable factors that affect taste then it puts the ratio measurement into better perspective for me. I shoot for a consistent ratio and temperature and then if it tastes strong to me I can usually adjust by adding a little room temp water at the end ;-)
Agreed about your second and third point, but the first point isn't exactly true. Measuring HOT volumes is nortoriously difficult, and will be 3% to 4% different than mass (assuming you have a volumetric measurement device that is certified accurate to higher temperatures). A pyrex measuring cup, or worse a plastic decanter, is going to be significantly wrong when used at high temperatures. They do not have adequate height to area ratio for decent accuracy. It's like trying to use a scale that only reads out to the nearest gram.
Measure out 1000g of water, it will occupy 1000-1010ml from a range of 0°C to about 45°C. Above that, it will occupy more and more volume, and at brewing temperatures (say 95°C on the upper end) will occupy about 1040ml.
AnotherSadDrip Said:
I have been struggling with the issue of water density for a couple of days now. I use a #6 filter cone and filter with a ratio of 66 g/liter--usually using either 33 g or 66 g of coffee depending on how large of a batch I am making. If I am understanding correctly, water has a lower density at higher temperatures. If I pour 1000 g of water at approximately 200* F, am I actually pouring less than 1000 ml? If so, is the difference negligible, or should I pour, say, 1004 g instead?
From what I've been able to gather, most of the measured volumes for coffee brewing are done at or slightly higher than room temperature. Maybe 20°C - 30°C, so the density issue for brew water is smaller than the actual variation that people can decant specific volumes. Mass is mass, volumes vary a lot unless you have hi-grade graduated cylinders - and even then they are only certified for working in particular temperature ranges.
I have a handful of different measuring devices, and pouring out 300ml in one pyrex may register about 290 in another, 315ml in another measuring cup. Something like a pyrex measuring cup is a simple, mass produced glass product with a printed graduation on the side. The variation between Pyrex and Anchor Hocking processes could probably fill a book by itself.
Bottom line - abandon thinking in volumes. When SCAA talks about "liters", then count these as kilograms or 1000g, and call it good. If you're using something like ExtractMojo, just switch everything over to grams and work from there. Extraction calculations, TDS% - all in mass, so suddenly switching to liters for the produced beverage and the brew water is not being consistent with measurement units.
Does it matter?
Well, at 65g/liter, or assuming 65g/1000g ~6.5% coffee brew ratio. If you instead count it as real volume and measure the brew water at 1000ml and 200°F, then it's really 65/0.963liters or ~6.75% coffee brew ratio. If you don't care about the difference between 65g/liter and 67.5g/liter, then no, it doesn't matter.
However, since you were thinking of making a 0.4% change in your brew water mass to make up for a potential variation, then it seems like it matters to you.
Here's a fun experiment:
Take your favorite measuring cup. Take some distilled water. Put the distilled water in your refrigerator (that puts it right around 4°C when fully cooled).
Then, tare your scale with your measuring cup on it. By eye, as carefully as you can, pour exactly some amount of your cold distilled water into the cup. 500ml is a good line to shoot for. 250 is even more challenging. Or even try for 100ml.
Record the actual mass of the cold water you poured in.
Do this 5-10 times. I think you'll be surprised at a couple of things:
-What you think is 500ml, 250ml or 100ml is probably not. -While you can get in the ballpark, your actual pour variation is more than you think.
Then, consider how close you can get to pouring exactly 500g according to your scale.
------------------------------------------ ----------------------------------------- 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
AnotherSadDrip Senior Member Joined: 6 Feb 2013 Posts: 3 Location: KS Expertise: I like coffee
Posted Thu Feb 7, 2013, 7:51pm Subject: Re: Water temperature, density, and mass
Thanks, guys, really helpful stuff. I had calculated approximately 4% difference in volume, which I might have been tempted to "fix", but after reading these posts, I can see why it's not worth it. Grams to grams it is, from here on out.
Symbols: = New Posts since your last visit = No New Posts since last visit = Newest post
Forum Rules: No profanity, illegal acts or personal attacks will be tolerated in these discussion boards. No commercial posting of any nature will be tolerated; only private sales by private individuals, in the "Buy and Sell" forum. No cross posting allowed - do not post your topic to more than one forum, nor repost a topic to the same forum. Who Can Read The Forum? Anyone can read posts in these discussion boards. Who Can Post New Topics? Any registered CoffeeGeek member can post new topics. Who Can Post Replies? Any registered CoffeeGeek member can post replies. Can Photos be posted? Anyone can post photos in their new topics or replies. Who can change or delete posts? Any CoffeeGeek member can edit their own posts. Only moderators can delete posts. Probationary Period: If you are a new signup for CoffeeGeek, you cannot promote, endorse, criticise or otherwise post an unsolicited endorsement for any company, product or service in your first five postings.
= No New Posts since last visit 