4: Physical Changes During Roasting

Roasting causes beans to change color, lose moisture, expand, and become brittle. While all professionals label roast levels based on bean color, there is no consensus on exactly what roast level each name indicates.

Color Changes

The first stage of roasting is commonly known as the “drying phase,” although beans lose moisture at similar rates throughout most of the roasting process. During the first few minutes of roasting, degradation of chlorophyll causes beans to change color from green to yellow. As roasting progresses, the beans change from yellow to tan to light brown, primarily due to Maillard reactions. Late in a roast, as the beans approach first crack, the brown color deepens due to caramelization. In a dark roast, carbonization may turn beans black.

Classic Definitions of Roast Degree

These beans were photographed at 1-minute intervals during preparation of a French roast.

During roasting, coffee beans change from green to yellow to tan to brown, and, if roasted very dark, black. No universal system exists for naming different degrees of roast; what one roaster calls a "light roast" another roaster may label "full city.”

Light roasts offer acidic, floral, and fruity flavors, more delicate aroma, and less body than dark

roasts. Dark roasts develop smoky, pungent, bitter, and carbonized flavors. If one takes roasting to an extreme, burnt flavors dominate and body declines.

The coffee industry’s lack of an agreed-upon nomenclature for degrees of roast causes confusion among roasters and consumers alike. I don’t claim to offer the “correct” definitions for different roast levels, but I believe the following descriptors represent common and reasonable interpretations of various roast degrees and bean colors.

Cinnamon

Cinnamon* roasts are generally dropped, that is, discharged from the roaster, sometime very early in first crack. Few consumers desire the green, grassy, often “peanutty” flavors of a cinnamon roast. However, some larger companies selling beans to cost-conscious consumers favor the very low weight loss of cinnamon roasts. In the cup: Very acidic, often “green” or “peanutty,” with grassy and floral aromas and very light body.

Left: Cinnamon roast, Right: City roast

City

City roasts are those dropped during the last stages of, or just after, first crack. Such roasts produce light-bodied coffee with very high acidity. City roasts are the current fashion among more progressive, or third-wave**, roasters and have historically been the standard in Nordic countries.

In the cup: Acidic, winey, sweet (especially if developed well), and juicy, with floral and fruity aromatics, hints of caramel, and light body. Can be grassy, lemony, and tart if not developed adequately.

Full City

Roasts discharged just before second crack and the appearance of surface oils are known as full city roasts. Many consumers prefer full city roasts because they offer a pleasing balance of moderate

acidity, mellow caramels, and medium body.

In the cup: Caramelly, with ripe fruit and medium body.

Left: Full city roast, Right: Viennese roast