Q: Context: When not used fresh, the rhizomes are boiled in water for about 30 -- 45 minutes and then dried in hot ovens, after which they are ground into a deep-orange-yellow powder commonly used as a coloring and flavoring agent in many Asian cuisines, especially for curries, as well as for dyeing. Turmeric powder has a warm, bitter, pepper-like flavor and earthy, mustard-like aroma.

Question: which part of the plant turmeric is obtained?
Let's give stream of consciousness below
The relevant sentence in the passage is: When not used fresh, the rhizomes are boiled in water for about 30 -- 45 minutes and then dried in hot ovens, after which they are ground into a deep-orange-yellow powder commonly used as a coloring and flavoring agent in many Asian cuisines, especially for curries, as well as for dyeing. So the answer is the rhizomes.