Matching Pairs Exam (Organic Acids)

Time: 40 Minutes
Passing Score: 75 Points

In the coffee organic acids matching pairs exam, students begin by sampling six of the acid components of coffee. The instructor presents a brief lecture about each. For the exam, students are presented eight sets of four cups of weakly brewed coffee. Two cups at each place setting contain an additional organic acid. Your goal is to select which two contain the acid AND identify the acid.

The six most common coffee organic acids used are:

  • acetic
  • citric
  • lactic
  • malic
  • phosphoric, and
  • quinic acid.

Acids may vary based on availability.  From these, four (4) are used in the exam:

  • Acetic acid is simple vinegar.
  • Citric acid is available in most vitamin shops.
  • Food grade malic acid, lactic acid, phosphoric acid are in pharmaceutical supply stores. Quinic acid, is sometimes found in pharmacies as an antimalarial drug.

Use a weak concentration of each in some mild coffee brewed at full strength, then diluted 50%. Pour the diluted coffee into four cups and then taint two of those four. Recognize later which two have the acid and you’re most of the way there.

As you seek to identify these acids and for use at your job later, remember the following:

  • Acetic acid is the compound that gives vinegar its pungent smell and sour taste. At low concentrations, it can be perceived as a mildly fruity flavor.
  • Citric acid is the dominant acid in, you might expect, citrus fruits. Look for its soury, citrusy characteristics in each sample.
  • Lactic acid is known as the milk acid, playing a role in biological processes from the souring of milk to the production of energy in human cells. I find that lactic acid is more easily detected as a texture, adding body to coffees.
  • Malic acid is the acid that contributes to the soury taste of green apples and tart taste in wines.
  • Phosphoric acid is a mineral inorganic acid used primary to add brightness to soft drinks.  Feel for a buzzing sensation on the tongue rather than a taste.
  • Quinic acid is the easiest to identify in the bunch, as it is the primary bitter compound in coffee, which is also lends its flavor to tonic water.

When taking the matching pairs exam, identifying the acid-tainted cup on each set is easy for an experienced cupper. Move quickly through the sets and follow your instincts.  The first selection is often correct.  Repetitive cupping of the acid solutions will fatigue your palate.  As with so many of these exercises, it’s always better to finish earlier than later.

For more information about the exam and setup, check out this online Q practice exam from Boot Coffee.