Thursday, September 17, 2009

Does processing method impact coffee flavor?

It makes sense, right? Processing affects the final flavor. Many things can go wrong between cherry and dried green coffee, most of which can be tasted in the cup. We all know this step is important. Nearly every source available says that the type of processing affects the final flavor. Most green bean suppliers pay homage to this general notion by providing processing information with their product. The Coffee Research Institute claims, “The processing method used on a coffee is usually the single largest contributor to the flavor profile of a coffee.” K.C. O’Keefe’s coffee quality formula puts processing at 10 percent of the creation step and lists processing and drying at a combined total of 55 percent of the conservation step.

So, if we all know it has an impact, what is the impact? How do we describe it? The Coffee Research Institute attributes nutty, sweet flavors to dry-processed Brazilian coffees when compared to wet-processed coffees from the same region. This agrees with the general sentiment about dry and natural processed coffees. But do we know this, or do we just feel it? Is there data?

I gathered cupping scores from Sweet Maria’s Latin American and African offerings and compared the averages of the dry-, natural-, and wet-processed coffees. The graph at the top shows those averages. Surprisingly, the wet processed coffees were sweeter on average, and dry-processed coffees were no more complex than wet coffees. Does this mean that any given coffee would be sweeter if processed wet than if it were processed dry or natural? Not at all. This only demonstrates the lack of good information.

The problem is that every location is different in climate, soil, management practices, and varieties grown, so even coffees from the same region are very different before processing. So when a taster tastes the coffee and says one is sweeter than the other it’s impossible to tell whether the sweetness comes from the processing or from the climate, soil, or variety. I have not found a single academic study that compared the various methods side-by-side. If anyone has solid information, let me know.

Over the next few months I’ll be gleaning what I can from the flavor literature, looking at what the possible impacts might be based on what scientific knowledge we do have. This is probably the biggest gap in current understanding of knowledge of quality along the coffee supply chain. Processing is an essential component of coffee quality, and the coffee world needs to know the different impacts the various methods have on flavor components.

Friday, July 3, 2009

Education Impacts Quality

Excellent flavor in the cup results from maintaining numerous quality determinants throughout the coffee supply chain. Quality begins prior to planting with a farmers' choice of variety and ends in the cup at the hand of a talented barista. At both points and at all points in between there's at least one thing in common. People impact quality. Furthermore, to a great extent, a person's level of knowledge determines their ability to either preserve or degrade coffee flavor at their position in the supply chain. And of course, knowledge is directly linked to education.

Monday, May 18, 2009

Coffee Craftsman

A person who practices or is highly skilled in coffee; an artisan.

coffee-to-water ratio

What's the proper grounds-to-water
ratio for brewing excellent coffee?

The most common recommendation floating around on the internet is the two tablespoons of ground coffee per 6 fluid ounces of water. But what if you want to brew a gallon of coffee, or even a half gallon? According to "Ratio" is defined as "a proportional relationship". However, when brewing larger volumes of coffee, the proportions of grounds and water are not scalable. For example, based on the 2 per 6 rate, 42 tablespoons of ground coffee would be required to brew 1 gallon of coffee.

Here's the math:
128 fluid ounces per gallon / 6 fl ounces = 21.3 fl ounce cups per gallon * 2 Tbl = 42 tablespoons of ground coffee.

Before dissecting the 2 per 6 rate any further we need to establish the amount of ground coffee per tablespoon. Even though the units of measurement are switching between mass and volume here, if we take into account the bulk density of ground coffee of 22 lb/cu. ft. (Sivetz, 1979), then we can calculate that 1 tablespoon of dry coffee grounds = approximately 0.38 dry ounces.

To obtain the bulk density of ground coffee we can take the average between coarse ground coffee (19 lb/cu ft) and that of fine ground coffee (25 lb/cu ft) resulting in an average bulk density of ground coffee to be 22 lb/cu ft.

We also know (from google) that there are 915 tablespoons = 1 cu. ft., then the number of ounces per tablespoon is of ground coffee is:

22lb/cu ft (16 ounces) (1 cu ft)
1 cu ft (1 lb) (915 Tbl) = 0.38 ounces/Tbls

Having established the amount of ground coffee per tablespoon (0.38 ounces) we can look deeper into the 2 per 6 ratio. The 2 per 6 ratio is equivalent to using 0.76 dry ounces of ground coffee for each 6 fluid ounce cup of coffee. Or, slightly more than 1 pound of ground coffee per gallon.
Furthermore, if we assume an absorption rate of 1 quart of water per lb of coffee, then the total volume of final brewed coffee is reduced to approximately 3 quarts. So, we would have used 1 lb of coffee to brew around 3 quarts of coffee. Seem like too much? That's because it is.
What do the authorities on the subject suggest? The Specialty Coffee Association of America (SCAA) recommends the following standards for certification as an SCAA approved "brewer".

  • The "standard" ratio of coffee to water for comparative purposes is 3.75 ounces per half gallon; 55 grams per liter; or 2.25 gallons per pound.
  • If coffee weights are measured in terms of "cups" (6 fluid ounces of water), the ratio of coffee to water for comparative purposes will be 10 grams or .36 ounces per cup. This equals 45 cups per pound.
Thus, instead of 2 per 6, or 0.76 ounces per 6 fluid ounces, the SCAA recommends 0.36 ounces per 6 fluid ounce cup. In other words, a little less than half of the 2 per 6 recommendation.

There are several key factors that affect flavor extraction, or more specifically brew strength, during the brewing process. Coffee freshness, grind size (and uniformity), water temperature, and grind bed dynamics (saturation), all play a role in the resulting cup quality. So, what's the take home here? The take home is that ratios, though proportional by definition, are not always scalable. This means that with regards to brew strength, the proportion of ground coffee to water do not maintain a consistent relationship along a graduating scale.

General References:

Sivetz, M.; and Desrosier, N.W. 1979. Coffee
Technology. AVI Publ. Co., Westport,
Connecticut, USA.

SCAA website.