Many of you are familiar with the "Coffee Brewing Control Chart," an example of which is posted below (thank you, SCAA):

What's the significance of the chart? Well, to brew the best coffee, most experienced tasters agree that you want to extract about 18-20% of the dry matter in your original ground coffee, AND you want to dilute it down to about 1.2 - 1.4% in the resulting cup of coffee.

Accomplishing both these tasks simultaneously is not trivial. Simply using a specified water to coffee ratio (eg, 16:1 by weight) is not enough. You also have to adjust the grind, brew water temperature and steeping time to hit your personal sweet spot (ie, EXTRACTION - solubles yield) for each coffee. It's sort of like hitting a dartboard from three or four times the regulation distance: without considerable practice, the target begins to get quite small, indeed.

My experience is that the extra effort is worth it. My brewed coffee definitely improved when I started experimenting with this.

But mostly I drink espresso. So posted below is the Espresso Brewing Control Chart.

This espresso chart differs from the coffee chart in several ways:

(1) The TDS scale (y axis) is in a much higher range, since espresso is so much more concentrated than brewed coffee.

(2) The Yield scale (x axis) reflects Solids Yield, rather than Solubles Yield, since espresso contains significant amounts of undissolved particles and emulsified oils.

(3) The brewing ratio calculation is different for espresso. For espresso, it's easy and practical to define the brewing ratio as coffee dose weight / beverage weight. For coffee, it's more practical to define the brewing ratio as coffee dose weight / brew water weight. This is because with coffee, one can conveniently measure the amount of water one adds to the grounds. In espresso, one normally can't measure the brew water directly, but it's easy to measure the weight of the resulting beverage.

Because these two calculations are similar yet different, it's useful to keep them from getting confused by referring specifically to Coffee Brewing Ratio or Espresso Brewing Ratio.

So, I hear you all saying (the roar is deafening), it's a nice chart, but why should I care?

Honestly, I'm not sure you should care, yet. But testing indicates that this approach may help us to control and understand how we get certain flavors in our espresso. For instance, rather predictably, espresso extracted on the low side of solids yield (say 15-16%) tastes sour for many light-roasted coffees and "green" for many darker-roasted coffees. Espresso extracted on the high side (say 20-23%) begins to taste harsh or bitter. Note that these observations are more or less independent of the espresso concentration (ie, ristretto or lungo), they refer to the percentage of solids that are extracted from the original dose.

How does one measure solids yield? In the first part of his landmark paper, Jim Schulman talked about oven drying used espresso pucks to determine how much of the original material had been removed. It's a tedious process, but gradually easier and faster methods are being developed, and they will soon be applicable to espresso. "Soon" means hopefully at the Atlanta SCAA show!

I know there are a lot of experienced coffee people who are skeptical of this sort of numerical approach to coffee and espresso. "Screw the numbers," they snort. "I go by my taste buds."

Obviously, the numbers can't possibly replace taste buds. They can only augment them, aid in quality control, and help in the diagnosis of problems. But I do know this: I have had many mediocre coffees at shops run by these snorting, experienced skeptics. And once their "golden taste buds" walk out of the shop, employees with less developed taste buds are left in charge. The results aren't always so golden. With the proper use of objective measurements, quality control at these shops could be greatly enhanced.

Notes:

a. Yes, the TDS numbers listed on the SCAA chart are off by a factor of 10. For instance, 1.3% is actually 13,000 parts per million, not 1,300.

b. Brewing ratios can be displayed in different ways. I use the SCAA method, with the coffee dose in the numerator, and the result expressed as a percentage (eg, 6%). Terroir Coffee, for instance, does the inverse when they calculate their "Brew Formula": coffee dose is in the denominator, and the result is expressed as a ratio (eg, 16.7:1).

c. If one knows any two out of the following three variables, one can always calculate the third: Espresso Brewing Ratio, Solids Yield, TDS.

d. The Espresso-style brewing ratio can also be used for brewed coffee, where it does have some advantages. But it isn't commonly done.