Sunday night science question

As many of you know, I roast my own coffee beans in a small roaster. We recently moved from southern California to Utah, going from about sea level in elevation to 6,000 feet.

In Utah the beans roast much faster than at sea level. This is with same beans, weight of beans, roasting time, and roaster.

So, why do they roast faster?

(My father-in-law knew, but then, he’s an engineer)


  1. High altitude coffee roasting is a method of roasting coffee at an altitude of 3,000 feet or higher.
    In roasting coffee, high altitude allows for quicker roast development at a lower temperature, avoiding the two most common problems of roasting coffee: baking, and scorching. Baking coffee occurs when it is roasted too long, causing inadequate structural expansion and resulting in flavor that is flat and lacks intensity. Scorching coffee occurs when coffee beans are roasted at too high of a temperature causing lack of development and resulting in flavor that is wild and woody. In roasting coffee, heat should be applied at both the lowest temperature possible and for the shortest possible amount of time. High altitude roasting helps accomplish that objective.

      • Roasting happens when the water contained within the bean is boiled. Water boils at a lower temperature at higher altitudes. So, it starts boiling earlier than when at sea level.

        As a comparison, the same beans take 15 minutes here vs 25 minutes at sea level.

        • There are a number of related kitchen phenomena you’ll observe up here:

          Pasta takes longer to cook (because the boiling water is at a lower temperature. Boiling water baths for home canning must be up to 10 minutes longer.

          Bread requires less yeast (and quickbreads and cakes require less leavening) for the same amount of rise, because you need less pressure inside the bread since ambient air pressure is lower.

          Many things, including brownies and cakes, should be cooked at a temperature 25-50 degrees lower to avoid burning, for the same reason your beans cook faster.

    • Water boils at a lower temperature at higher altitudes. So it started boiling sooner than it would at at sea level, and kept doing so unril the end of the timing cycle. Which means the beans were heavily blackened, not dark brown like I like them.

      The darker the roast, the less you are tasting the bean and the more you are tasting the roast.

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