Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn this reading yet, so here's a mnemonic to help you:
The most coarse thing you can think of is a rock (あら). You rubbed it on your face and it was really rough and kinda painful. You probably shouldn't be rubbing a rock on your face, actually.
I always use the coarse flour from corn, wheat, or beans in my smoothies.