Verification of Development Using a Refractometer

A coffee’s extraction potential depends on roast development. Inadequate development will limit a bean’s solubility, and hence its extraction. For example, let’s say you roast two batches of a coffee to the same color and pull several espresso shots from each batch using identical inputs (temperature, time, ground weight, shot weight, and so on). If batch A consistently yields extractions near 19.0% and batch B averages 16.5%, batch A is almost certainly more developed than batch B. In such a case a refractometer offers objective verification of roast development.

The coffee refractometer has had more impact on coffee quality than any other invention in decades.

All the principles of roasting on a large machine apply to sample roasting. Many owners of small roasting businesses have commented to me that they usually prefer the coffee made from their sample roasters to that made from their production roasts. That’s not surprising, because sample roasters often have more power than small shop roasters, relative to the small batches they roast. A high ratio of gas power to batch size facilitates good development. However, most sample roasters have rudimentary controls, making consistency challenging.

Most older sample roasters offer the user only two controls: a manual knob to control the gas setting and an environmental probe. To make the most of such a machine, I recommend using the following procedure:

1. Stabilize the roasting environment at one particular temperature between 410°F-420°F (210°C-216°C), with the drum empty before charging.

3. About 30 seconds before first crack, decrease the gas by approximately 40%. If this produces a very fast roast (less than 8 minutes) or a very slow one (more than 13 minutes, which is slow for a sample roaster), try changing the pre-roast stabilization temperature.

This strategy is simplistic but often yields surprisingly good results and consistency, given that the operator doesn’t have much feedback or control while roasting.

Ideally, one should use a bean probe when sample roasting. Beware, though, that in many sample roasters it may be difficult or impossible to immerse the probe in the bean pile sufficiently to produce reliable temperature readings. If your sample roaster doesn’t already have a manometer or other precise indicator of gas setting, I recommend investing in one. When using a sample roaster with adequate controls (bean probe, air probe, manometer, and so on), one can roast exactly as one would in a production machine, though one might consider using faster profiles with a sample roaster.

Cupping is a systematic, somewhat standardized, method of evaluating coffee. Cupping requires no special equipment, is easy to replicate, and is accessible to anyone with a grinder and hot water, whether she is a coffee farmer in Ethiopia or he is a barista in New York. The process allows the cupper to brew small samples and compare them rapidly, going back and forth between cups as needed.

The following is one effective version of standard cupping procedure. You may prefer to vary some of the details, but, regardless of your exact method, please treat every sample identically.

You will need: a hot-water kettle, cupping bowls or glasses with capacity of 6-10 oz (175-300 ml), cupping spoons, one spittoon per cupper, cupping forms or notepads, a timer, a grinder, a gram scale, and a few tall cups filled with water for rinsing spoons.

2. Plan to taste as many as five or six samples, but ideally no more than that, in one session.*

3. Grind 10.0 g** of each coffee into an 8-10 oz (235-295 ml) widemouthed glass or ceramic cup. The grind should be medium-fine, similar to an appropriate manual-pourover grind; I recommend using a refractometer to determine the grind setting that produces your target extraction.

4. Sniff the fragrance of each sample. The most volatile aromatics, or those with the lowest boiling points, make up the dry aroma. Its intensity indicates the freshness of the roast and grind.

5. Once the kettle boils, remove its cover and allow the water to cool to 204°F-205°F (96°C), before pouring. (This usually takes about 45-60 seconds, or longer for larger kettles.)

8. Pour 170 g of water over the grounds such that the water’s turbulence mixes and wets all the grounds. (Alternatively, use '7 g of grounds and 120 g of water in smaller cups.)

9. Bring your nose close to the coffee’s surface and sniff. At this moment, the coffee offers the most aroma. Don’t miss it.

11. After 4 minutes have elapsed, “break the crust” of the cups in the order in which they were poured. To break the crust, dip the bowl of a cupping spoon halfway into the coffee, push aside the crust of grounds with the back of the spoon, and bring your nose close to the surface of the coffee without touching the grounds with your nose. Sniff the aromatics released as you break each crust.

12. Inhale slowly and deeply as you break each crust. Long, slow inhalations provide better aroma detection than short sniffs.33 Take notes on your impressions.

13. After breaking all the crusts, remove the grounds, foam, and oils from the surface of the cups. An efficient method is to skim the surface using two cupping spoons simultaneously.

14. At 9:00, begin tasting the coffees. Dip a cupping spoon just below the surface of the coffee, raise it to your lips, and vigorously slurp the coffee, spraying it throughout your mouth. (Many cuppers prefer to wait for the coffee to cool further before sampling. I recommend tasting the coffees at the highest temperature you can comfortably tolerate, but not before 9 minutes have elapsed. It’s advantageous to taste the coffee at a wide range of temperatures.)

15. Focus on the coffee’s aromatics, mouthfeel, flavor, and other impressions. Take notes.

16. Spit out the coffee. If you’re not sampling too many coffees in the session, consider swallowing the occasional spoonful. Swallowing promotes retronasal olfaction33 and ensures the cupper exposes his farthest-back taste buds to a sample.

17. Move on to the other coffees, slurping and spitting as needed to get sufficient impressions of all of them. There is no need to “cleanse the palate” between each slurp, but swishing some water in the mouth every few minutes may help refresh the taste buds and forestall palate fatigue.

19. Take a break for a few minutes. Slurp and spit the coffees again when they are lukewarm.

20. Allow the coffees to cool to room temperature, about 15-30 minutes, and repeat the process of slurping and spitting. You will find the coffees offer much new information after they have cooled.

I recommend cupping coffees the day after they’re roasted, if possible. Cupping should always be

done blindly, meaning the cuppers do not know what coffees they are tasting. To set up a blind cupping, label the cup bottoms before pouring the water, or have someone who will not be tasting the coffee arrange the cups. Everyone is susceptible to bias, so blind cupping is the only way to ensure a fair evaluation of coffees. Blind cupping is also the most effective way to learn and to improve one’s tasting skills.

The one unbreakable rule of cupping is that all coffee samples must be treated identically; all cups should have the same grind setting, ground coffee weight, water weight, steeping time, and so on. One who executes a cupping properly can be confident that all the perceived differences in the cups are inherent in the coffees and are not artifacts of the cupping process. Something as simple as pouring 10 g more water into one cup than another (easy to do, as you’ll find if you weigh your filled cups) may noticeably alter a sample’s extraction, flavor, and body.

One may also cup to test the effect of changing one variable, such as grind setting, variety of green coffee, roast profile, brewing temperature, and so on. As long as the only difference among the cups is the variable being tested, the cupping will be valid and offer useful information.

I recommend using a refractometer to equilibrate your cupping extraction level with your typical brewing extraction. For example, if you prepare your espresso and drip brews at 20% extraction, you should cup at 20% as well. However, I recommend cupping at lower brew strength than you likely prefer. Brew strengths of approximately 1.15%-1.35% are strong enough to give a cupper a fair impression of a coffee’s body but dilute enough to offer excellent flavor clarity. Most professionals prefer drinking stronger brews, but additional brew strength may hamper one’s ability to discern subtleties in a coffee. To me, cupping isn’t about maximizing enjoyment as much as it is about optimizing one’s ability to analyze coffees (though I hope it’s enjoyable too).

Left: Extraction measurements of a recent cupping / Right: Judge Bobinski’s score sheet

Each phase of a cupping offers a different perspective on its samples. Take full advantage of all the phases to get as much information as you can about the coffees on the table.

Smelling the dry grounds may indicate whether a sample was overroasted or if the roaster used insufficient airflow. The fragrance may also hint at the coffee’s bouquet and fruit notes, as well as some defects due to age, ferment, or underripe cherries.

The sooner you can smell coffee after the water contacts the grounds, the better. Release of aromatics is correlated with temperature, and coffee offers its peak aroma when it is hottest. I find this moment also provides the best opportunity to sense underdevelopment. If the aroma is savory or vegetal upon

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