Learn Farsi: می‌خواستم حرارت را زیاد کنم، اگرچه دانه‌ها تیره بودند. - I was going to turn up the heat, although the beans were dark.

Concessive conjunctions like اگرچه (although) can be followed by either the indicative or the subjunctive mood. You use the indicative—like بودند (they were) here—when stating a concrete, established fact. Because the speaker knows the beans were definitely dark, there is no doubt or hypothetical meaning that would require the subjunctive.

Since the sentence is in the past tense ("I was going to"), why is زیاد کنم in the present subjunctive rather than a past tense?

In Farsi, the second verb in a "wanting to" or "going to" construction is almost always in the present subjunctive, regardless of whether the main verb is past, present, or future. می‌خواستم sets the past timeframe, and زیاد کنم acts as the action being desired.

Why does می‌خواستم translate to "I was going to" rather than "I wanted to"?

Literally, می‌خواستم does mean "I wanted to". However, pairing the past continuous of خواستن (to want) with a subjunctive verb is the most natural and common way to express a past intention in Farsi, which translates smoothly to "I was going to" or "I intended to" in English.

Is دانه the specific word for a coffee bean?

If you mean a bean you eat like a vegetable (kidney bean, green bean), Farsi uses لوبیا. But دانه broadly means "seed" or "grain", and it is the exact word used for coffee beans. The context clues here—حرارت (heat) and (dark)—make it clear the speaker is roasting coffee.