The caffeine in coffee stimulates the production of irritating acid in the stomach. But darker roasts of coffee, produced by roasting the coffee beans longer, contain more N-methylpyridinium (NMP) than lighter roasts, and NMP tends to suppress production of acid in the stomach. Therefore if you drink caffeinated coffee, darker roasts will irritate your stomach less than lighter roasts.
The answer to which one of the following questions most helps in evaluating the argument?
Does extending the roasting time of coffee beans increase the amount of caffeine present in the brewed coffee?
Here’s our additional factor. Dark roasts might have more NMP, which pushes toward a happier stomach, but what if they also mean more caffeine?
In classic LSAT fashion, getting here requires a few logical connections. You need to remember
Does a reduction in acid production in the stomach have an adverse effect on stomach function?
This answer choice is tempting if your idea of the conclusion is “dark roasts are better for your stomach than light roasts”. But our conclusion is narrower. It’s about stomach irritation, not stomach function. These are distinct concepts.
Would coffee drinkers who drink caffeinated coffee increase their coffee consumption if the coffee they drank contained less caffeine?
The premises don’t tell us whether light or dark roasts have more caffeine. (Tricky, perhaps, because you might have answer choice (A) in your head still.)
Without that information, though, we can’t tell which direction (C) cuts. Maybe they have the same amount of caffeine and (C) has no effect either way.
Do some coffee drinkers who switch from lighter to darker roasts of coffee increase their daily coffee consumption?
(D) is relevant to the question of whether living the dark roast lifestyle irritates your stomach less than living the light roast lifestyle. But our conclusion is about the baseline impact each roast has on your stomach, holding amounts constant.
Do lighter roasts of coffee have any important health benefits that darker roasts of coffee lack?
Like (B), this answer choice is tempting if your idea of the conclusion is “dark roasts are better in general than light roasts”. Perhaps these health benefits are an additional factor weighing in favor of light roasts!
But our conclusion is narrowly about stomach irritation, not general health.