On Roasting, I: Speaking Generally

If your mind is empty, it is always ready for anything; it is open to everything. In the beginner’s mind there are many possibilities; in the expert’s mind there are few. If you discriminate too much, you limit yourself. […] This is the real secret of the arts: always be a beginner. Be very very careful about this point

Disclaimer: All times and temperatures are relative and can greatly vary dependent on the context of the roasting method, machine & batch size you use.

There exists a steady decline in quality from the moment a coffee cherry is picked. A roaster cannot impart anything more than what is already within the seed. In other words, I believe a coffee’s potential is predetermined by the time it reaches us as roasters. A skillful coffee roaster will work to showcase what a coffee is while avoiding the defects of roasting poorly.

Properly developed coffee can be defined as an achieved evenness of the seed at the end of a roast. In other words, a coffee is properly developed once it passes the stage of under development and before it enters over development.

Note: F.C. = First Crack

Coffee Density

p = m / V (density = mass / volume)

Why is dense coffee generally good coffee? Usually it is because it comes from a healthy fruit that was on the tree for a longer time and matured slower. Therefore the cellulose pockets that form the green beans structural matrix are more tightly-packed and small. High altitude coffee and/or well-shaded coffee trees tend to slow fruit maturation because of limited light and colder climate. The opposite of dense coffee is called soft coffee, which is grown in a lower, hotter climate and thus reaches maturity more quickly

To gauge a coffee’s density, grab two pint glasses. Fill one to the brim with a coffee that you know roughly how dense it is (as a point of reference); fill the second pint glass with the coffee you are trying to determine how dense it is. Determine (e.g. in grams) the weight of each coffee and divide them by their volume (volume of a pint glass = 16 oz = 454g).

Determining how dense a coffee is will help you to estimate an appropriate charge temperature and a basic roast profile.

Note: A coffee that is more dense can generally handle a higher charge temperature. The more dense a coffee is, the slower it takes on heat. This is analogous to building a fire where the more dense, greener log burns very slowly compared to to a weathered, less dense one.

Charge Temps: Using your “First Crack” temp as a point of reference, with a batch size of about 70% of drum capacity, I tend to lump charge temps into two basic categories:

  • A higher altitude coffee, one that is more dense: use a higher charge temperature (that is, above it’s F.C. temp) with a lower flame at charge, OR
  • A lower altitude coffee, one that is less dense: use a lower charge temperature (sub F.C. temp) with a higher flame at charge.

Roast Defects

  • Tipping refers to a roast error that can be discerned by inspecting the roasted coffee, where the ends of the elongated bean appear burnt (where the coffee seed would germinate from: it’s softest spot). It can easily be perceived in the cup through burnt or smoke flavors, or a lack of sweetness
  • Scorching refers to patches of discolored burn marks on the coffee bean, due to a high-heat roast environment or other roast error. Oftentimes caused by too much conduction (the drum is too hot).
  • Baking refers to flat-lining the roast which tends to flat-line the coffee’s acidity.
  • The use of too much airflow (or) not enough airflow can do many things. For example, too much airflow can either create too much momentum in a roast or completely flat-line it (or cool the whole thing down, depending on how powerful your fan is!). Too little airflow may choke out your flame, smoke out your coffee, or create too much conduction between the beans and the roasting drum.
  • I personally consider under development and over development to be roast defects, although these terms are a bit slippery and subject to interpretation.

Thermal Equilibrium

  • Maintaining thermal equilibrium between batches is essential to consistency and is necessary in order to maintain a baseline thermal profile to observe and to begin profiling.
  • Thermal equilibrium between batches will change as a production day unfolds (e.g. heat is contained more easily within the drum between the 10th and 11th roast of the day vs. the 1st and 2nd).
    • If roasting on a manual, cast iron drum: As the drum’s ability to retain heat increases, I tend to turn the burner off completely after each roast and allow for at least a minute or so to elapse before turning it back on and slowly climbing to my next charge temp.
    • At the beginning of the day, I find that I can spend less time between each batch because the drum loses heat much quicker.
    • Towards the end of a production day, the drum has such efficient heat retention, if I charge batches too quickly one after the other, my roasting curves are condensed (that is, my turning points are higher, my roasts are quicker, and my overall development is lower).

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