July 30, 2021
Roasting Coffee is a complex skill that very few people have mastered

How to roast Coffee

Be warned! These are my notes as I try to figure out how to do it. Hopefully I will revise them as I gain experience.

Here is a great video:

Various links (2021): Some more in 2022:

My notes on the Sweet Maria video

Washed coffees tend to look green and naturals are more yellow. To learn some things (not produce great coffee), someday roast a batch of coffee on the stove in a cast iron skillet. No noise from fans or motors. Everything is easily visible. You must have good light to roast coffee. You must have a timer.

First crack is mostly water vapor, second crack is mostly carbon dioxide. A lot of air roasting can go too fast and blur 1st and 2nd crack together. Look at the color of the center crease. Or better yet, don't look at it -- it can be misleading as there is usually some chaff trapped there that will deceive you. Look at the surface texture as well as color.

Dark roasting drives out oils, but this is a loss -- and the oils then oxidize.

At first, roasting is endothermic as you need to push in energy to drive out water, but at first crack things flip and become exothermic and the coffee begins to roast itself. With some coffees, especially naturals, you may not hear any cracks.

Roast Levels

There is all kind of ambiguous and non-uniform lingo. You hear about a "medium" roast, or a full city, or "french" roast. Different roasters have different interpretations about what these terms all mean. Nonetheless I will aim to give a general guide here, but the real experts will give you their interpretations if you check these links. You also hear about first and second crack and as a roaster you need to correlate these events with the above roast levels. Here is a stab at it:

If you stop the roast right at the very start of first crack, you get "Cinnamon Roast", which is drinkable but underdeveloped.

If you stop the roast in the middle of first crack, you get "City Roast". This is good if you want to be able to clearly taste origin flavors and compare different coffees.

If you stop the roast in the very end of first crack, you get "City Roast +". The beans will have no oil and you should still be able to distinctly taste origin flavors.

If you stop just before second crack, you get "Full City" ("Medium" roast) If you get a few snaps of second crack, you get "Full City +". You might get a bit of smoke and see a few tiny bits of oil on the beans. This is a popular roast level as you get a mix of origin flavor and roast flavor.

If you stop with a rolling second crack, you get "Vienna Roast". You will have plenty of smoke and the beans will have a clear sheen of oil. Little of the origin flavor is left. Indonesians beans are an exception and may maintain a clear flavor even if roasted this dark.

Beyond this we have French and Spanish roast, but I think it is a crime to roast even to a Vienna roast so I won't even talk about these. Once you get to French roast, it matters little at all what bean you began with, you are just going to have a French roast taste. I view anything in the Vienna, French and beyond territory as a "roasting accident" and reserve such beans for emergencies only.

The mistake the person new to this might make is thinking that darker roasts are better. Charbucks certainly exploits this. Darker roasts may indeed yield a darker cup with a stronger flavor, but you have to decide if burned coffee is your thing.

The caffeine content "per bean" is the same in dark and light roasts, so don't be fooled into thinking that darker roasted coffees have more caffeine. Brew methods have more to do with caffeine with cold brew having the most caffeine and espresso the least, but we are drifting off topic.

Rao's Three commandments of coffee roasting

  1. Apply adequate energy at the beginning of a roast
  2. Bean temperature progression shall always decellerate
  3. First crack shall begin at 75-80 percent of the total roast time
Another writer boils down Scott Rao's teaching as:
  1. Watch your rate of rise (bean temperature), it should steadily decellerate.
  2. It is all about development (time after first crack)
  3. Minimize use of the trowel (don't interrupt the roast)
  4. Increase airflow as the roast progresses
  5. Cupping is king - learn to analyze your results

Three phases of the roast

First there is the drying phase. Green coffee contains about 12 percent water. When coffee is first introduced into the roaster, the first thing is to simply raise the temperature of the cool coffee to the temperature of the roaster. When the temperatures match, this is referred to as the "turning point". Then drying begins and the temperatures rise in parallel. The color of the coffee changes from green to yellow as it looses water as steam. This should take about 40 percent of the roast time. Reduce the heat at the end of the drying phase to avoid rushing the next phase.

Second is "carmelization". This happens during the interval between the beans turning yellow and first crack. The Maillard reaction causes the beans to turn brown and a variety of other reactions produce the taste and aroma that we look for in roasted coffee. This stage is critical and should not be rushed.

Third is "development" and begins at first crack. First crack takes place at 370-390. Beware stalling the roast in first crack and ending up with baked coffee - which is not good. Lots of reactions occur quickly and how fast they occur is determined to a large extent by the "momentum" of the roast. The beans have enough heat to essentially roast themselves from the inside. How long this phase is allowed to continue determines the level and darkness of the roast. You only get maybe 15-30 seconds between first and second crack, so you need to pay attention.

Maillard reaction

This gets technical. An amino acid and a reducing sugar react. This is driven by the heat of roasting. It happens in toasted bread and numerous other foods as well as in coffee. It is what gives us the brown color. Compounds called melanoidins are developed. These are brown nitrogen containing polymers. The longer the time given for Maillard reactions, the more of these are formed. More of them give the coffee more viscosity and takes off the edge given by unreacted organic acids. Unreacted organic acids are what make coffee bitter. Darker roasts are less bitter by virtue of giving more time for these organic acids to react and degrade to other compounds.

Outgassing

Coffee will outgas and develop for a day or more after roasting. Carbon dioxide will be released and provision should be made to let it escape (don't seal up fresh roasted coffee). Coffee may continue to expand after roasting, this is especially true of darker roasts.

Have any comments? Questions? Drop me a line!

Tom's coffee pages / tom@mmto.org