Bottom four-dots-of-fire radical (
灬 = compressed
火, Kangxi #86) — the indexing radical. Pictures flames licking up under the smoking chimney above, completing the image: fire at the bottom, smoke rising through the flue, food or object darkened on the way up. Same radical groups
热,
煮,
蒸,
焦,
然 — all heat-and-cooking chars.