Posted Sat Oct 6, 2012, 1:02pm Subject: Yield Ratio, EBR, and Definition of Espresso
So, I've been playing around with converting the Traditional Brew Chart into a chart based on mass yield ratio.
Mass yield ratio is the ratio of Produced Coffee to Brew Coffee.
(remember that "brew coffee" is the dry ground coffee ready to be combined with brew water, and "produced coffee" is the coffee solution or beverage that is in the pot or cup after brewing).
Then, to achieve a particular yield ratio, all you need to know is what your typical absorption is, or just add the water you need to achieve a particular amount of coffee.
This really simplifies the relationship between strength, extraction and yield ratio - it's basically the only way to work when it comes to espresso, as the amount of brew water is generally unknown for espresso (as is the typical absorption for the process of making espresso).
AndyS (I believe) pioneered the thinking of using EBR (Espresso Brew Ratio) or the inverse of yield ratio - the ratio of brew coffee to produced coffee - and he expressed this ratio in percentage.
So, if you can measure the strength of the produced coffee, and you know the yield ratio or EBR, then you know the extraction.
Define: Y = Yield Ratio (Produced Coffee / Brew Coffee) EBR = Espresso Brew Ratio (Brew Coffee / Produced Coffee, expressed normally as a percentage) C = mass of Brew Coffee P = mass of Produced Coffee E = Extraction = TDS / Brew Coffee
Using 14g Brew Coffee, you yield 28g of espresso. The EBR is .50 or 50% (14g coffee / 28g produced) Y = 2.0 (28g produced / 14g brew coffee)
If you measure the strength at 10%, then the extraction is 20%. (28g * .10 = 2.8g TDS, 2.8g TDS/14g brew coffee = 0.20 = 20%)
If you measure the strength at 9%, then the extraction is 18%, and if you measure the strength at 11% then the extraction is 22%.
Simply stated: E = S / EBR = S * Y 0.10 Strength / .50 EBR = 0.20 Extraction = 20% 0.10 Strength * 2.0 Yield Ratio = 0.20 Extraction = 20%
Furthermore, this puts every percolation method extraction and strength into a chart that is defined COMPLETELY by three variables and one equation. Know two, and you know the third.
Then, I started plotting these variables, and since they are a set of three values as ratios (much like Ohm's law, V = I*R, or R = V/I or I = V/R) they will produce a plot that is linear on a log/log chart.
The neat thing is you can plot a line for 20% extraction, 18% extraction and 22% extraction, and begin to think about the physical limits of brewing coffee.
For example, what exactly does 140% EBR mean? Well, it means you will use 140% more mass of brew coffee than you will produce: 21g dose (near maximum for a triple size basket), 15g shot in the cup. If this is done properly, it will take 25 seconds to produce, and this means the process will be making less than a half gram of espresso per second. That is a really slow production rate - but since the initial 10 seconds produces about half of the final amount of any shot - the last 20 seconds must be darn near drops.
We know that the practical range for most coffee-related refractometers are about 20% strength. That is really stout stuff, there, I doubt many people are actually making miniscule yielding espresso at 20% strength. So, I figured out that the practical limits are right there, on the chart.
Furthermore, we can plot some of the interesting points on the chart - a conversion scale for EBR and yield ratio, and also the other interesting finding:
When it comes to espresso, there's "modern" espresso, and there's "traditional" espresso.
Most standard espresso (even though it is frustratingly parsed in VOLUME instead of properly defined in MASS) is based on the "single" shot - 6.5-8.0g of coffee, produces 28-35ml of espresso (which contains crema - foam that weighs practically nothing but occupies about 7-12ml of volume - IF you can read the volume well before the crema begins to break). On average, these will have a mass in the range of 18-24g - implying a traditional single shot EBR of somewhere between 20% and 40% (or a Yield Ratio of 5.0 to 2.5). A double shot just doubles the coffee, but ends up with the same EBR or Y (essentially doubling the produced coffee).
When you go to a shop with a superauto machine (yes, like Starbuck's) or if you have a Gaggia or other home superauto, they are also in this same range for espresso. However, if you head to a modern cafe with a real barista behind the counter, dosing and tamping and properly pulling the shot, you might end up with a richer, stronger espresso. In traditional terms, this was called a "ristretto", and ends up with a significantly lower yield and higher strength.
Furthermore, if you take the same 25 seconds but produce more espresso from the same amount of coffee (where the EBR is below 20%), this is called a "lungo" or long shot - more coffee at a lower strength, made with the same parameters that espresso is produced with (8-9 bar, 90-95°C, 25seconds).
It appears that today's normale is yesterday's ristretto. EBR for the traditional ristretto is above 40%, but this looks like the beginning of the range for a modern (some may call it "3rd wave") normale. Additionally, today's "lungo" is yesterday's "normale". With the rise of artisan coffee shops, there is a definite trend toward updosing and serving up stronger, richer espresso.
The lines between single and doppio are also blurred.
The traditional single was from 6.5-8g of coffee, a double from about 13-18g of coffee, and more than that up to 22g is a triple.
Today's typical artisan hand-made meticulously pulled shot might be 14g brew coffee to produce about 25-30g of espresso - maybe around 9-11% strength. In old terms this would have been a "doppio" or double ristretto, but today it would not be out of place as representative of a single shot.
BTW - it is easier to produce doubles than singles - errors in dosing are reduced (percentage wise), and it is easier to control the process. Starbuck's machines typically perform better if they are producing double shots.
So, here's a single chart that summarizes what I think I'm teasing out with regard to "defining" espresso. I identify traditional vs modern ranges, and practical limitations for properly extracted espresso are defined by:
20% strength or less 17% extraction or more
At this point, this implies a practical limit for EBR around 0.20/.17 = 1.176 or 117.6% or less. (Yield ratio of 0.85 or higher) - this means that the TOP end of modern or traditional ristretto is EBR <117%.
Above this, it is impractical to measure strength since the range limitations for most refractometers built for coffee are established at 20% (Based on my VSTcr).
I am aware that some people hate when numbers start to get put onto a traditionally "artisan" endeavor - but since I'm having such a difficult time getting a definition of "espresso", I figured I'd put this together and tack it up on the virtual dartboard for potshots.
(Click for larger image)
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