This post lead to a few private comments, questions, or clarifications, as well as some question on Brew Ratio. I decided to post something to define how I use brew ratio.
First of all, brew ratio is not a single dimensionless number for the classic brewing control charts. The actual recommendations are with a set amount of coffee (by weight) and a set amount of water (1/2 gallon, by volume, undefined temperature most of the time though recently there have been notes that the volume is "hot"). The SCAA brew control chart has X oz (avoirdupois) of coffee and Y fl. oz of brew water (and a corresponding metric translation, based on 1.9 liters of water, X g of coffee). The SCAE brew control chart uses X grams of coffee per liter of brew water.
Furthermore, these are prior to brewing, and some methods are prone to more evaporation than others.
When I am setting up a particular brew, I will test the system to determine the method's evaporation and typical loss. On an inverted aeropress, this is generally around 1g in 280g total, where my BCM-4C is more like ~15g of water lost to evaporation in ~500g total. A cupping may lose about 6g to evaporation during cooling (in about 180g). While unlikely, some methods may have lost coffee solution, but brewing carefully this can be controlled fairly well.
Any particular brew of coffee, if used for research/investigations, should be easily controlled to eliminate loss of coffee solution during brewing. Evaporation is much more difficult to control. I admit that much of my investigations use a brew ratio with coffee and the starting brew water - this works fine if the evaporation loss is small like on inverted AeroPress. However, in retrospect, the brew ratio is probably best established when the produced coffee and the grounds are measured.
If coffee solution loss is minimized, and the spent grounds and coffee produced are measured immediately, then the brew water is the sum of the produced coffee and the spent grounds minus the original coffee mass.
Then, there is the question of how to express brew ratio - as a percentage mass of the coffee to brew water (to keep them in whole numbers)? Or should it be grams of water to grams of coffee? Mathematically, they are inverse of each other - it is arbitrary which one is used. VST uses a "brewing formula ratio" of mass of water:mass of coffee. I've referred to brew ratio, or brew percentage as coffee : water expressed in percentage.
Before Brewing: W = mass of brew water C = mass of brew coffee (this is the starting, dry, ground coffee)
If neglecting loss: B = Coffee Brew Ratio, ratio of brew coffee mass to brew water mass = C / W, and generally expressed as a percentage. (Example: If C = 55g, W = 1000g, B = 0.055 or 5.5%)
R = Water Brew Ratio, ratio of brew water mass to brew coffee mass = W / C, generally 18.5 or less. C = 55g, W = 1000g, R = 18.18
If loss is significant (>10g for any brew method or >2.5% for small brew batches), then I usually assume that B and R will be "effective" at the end of the brew cycle (i.e. W is defined by the difference of G + Cp and C)
Based on an assumption that coffee loss is zero (only evaporation loss, or loss of brew water only):
W + C - L = G + Cp at the end of brewing. L (the loss) is grams of brew water lost in the brew process due to evaporation.
Loss, L = G + Cp - C - W
Effective Water Brew Ratio is therefore:
(W - L) / (C) or (G + Cp - C) / C
I can provide an example or two if requested - otherwise this may be of interest to those following calculations and predictions of modelling the brewing process.
------------------------------------------ ----------------------------------------- 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
calblacksmith Moderator Joined: 25 Nov 2007 Posts: 5,681 Location: Riverside, Ca, U.S.A. Expertise: I live coffee
Espresso: ECM Veneziano A1 Grinder: Many different commercial Vac Pot: 40s era Silex Drip: Milita, Bunn&Curtis... Roaster: Cast iron pan, gas burner
Posted Fri Aug 3, 2012, 4:46pm Subject: Re: Brew Ratio - A Few Notes
Interesting.
Have you found the percentage of disolvable solids to be constant across the spectrum of brew methods regardless of temp or are they lower with cold brew method vs hot methods? After all, it is the% of solids that we taste and are seeking to optimize in the cup.
We use brew ratio to reach optimal solids for each method and my guess is that cooler brewing requires a more dense ratio of c to w because I postulate that the solids are more readily disolved in hot water.
In real life, my name is Wayne P.
Feed the newbs, starve the trolls and above all enjoy what you drink!
Posted Sat Aug 4, 2012, 8:55am Subject: Re: Brew Ratio - A Few Notes
calblacksmith Said:
Interesting.
Have you found the percentage of disolvable solids to be constant across the spectrum of brew methods regardless of temp or are they lower with cold brew method vs hot methods? After all, it is the% of solids that we taste and are seeking to optimize in the cup.
We use brew ratio to reach optimal solids for each method and my guess is that cooler brewing requires a more dense ratio of c to w because I postulate that the solids are more readily disolved in hot water.
In a nutshell - temperature and time are important and interactive. Temperature will adjust the time portion of dissolution, as well as the particular molecules that are dissolved. Time is method-dependent on its effects.
It is possible to get good strength out of cold brew methods - the temperature stretches out the rate of dissolution, but also reduces the melting/emulsification of long-chain lipids (the fats that are more solid at room temperature), which also coincidentally contain some desirable and some undesirable tastes.
The %TDS is an excellent proxy for the taste of coffee, but what these dissolved solids actually contain are altered by the brew method. Even at the same brew ratio and strength, same contact time, the same coffee evaluated at the same temperature using the same method (the easiest common method would be timed immersion with a distinct filter step) - but brewed at different strike temperatures will have (in my experience) variations on flavor that non-experts can detect.
<shrug>
------------------------------------------ ----------------------------------------- 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
calblacksmith Moderator Joined: 25 Nov 2007 Posts: 5,681 Location: Riverside, Ca, U.S.A. Expertise: I live coffee
Espresso: ECM Veneziano A1 Grinder: Many different commercial Vac Pot: 40s era Silex Drip: Milita, Bunn&Curtis... Roaster: Cast iron pan, gas burner
Posted Mon Aug 6, 2012, 12:27pm Subject: Re: Brew Ratio - A Few Notes
After I typed my reply I realized that I had neglected time in the brewing process.
I have never cared for cold brewed or cold coffee such as in ice cream. It appears that the different flavors that are extracted at low temps, are not agreeable to me. I can see how the fats dissolve differently with temp. A nice brew made hot also does not taste good to me at room temp and it may again be the long chain lipids that change with temp.
I tend to favor the vac pot method of brewing followed by filtered drip and inverted Aeropress (when not discussing espresso) I can see how mouth feel plays a very important part in how I enjoy coffee, for me, I like a clean cup without fines yet I prefer the oils in a brew filtered in coffee grounds such as a Vac pot VS a paper filter but the fines in a press pot leave me cold.
I have also done some cupping and have seen how the flavor changes as the brew cools, for me, hot coffee is the only way to drink it, regardless of the ambient temp.
You have given me something to dwell on, to try to understand the differences of what I am tasting and why I do or do not enjoy it. Yet another compartment in this Pandora's box we call coffee has been opened for me!
In real life, my name is Wayne P.
Feed the newbs, starve the trolls and above all enjoy what you drink!
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