turn to ashes in your mouth become bitterly disappointing or worthless.

☞ This phrase alludes to the Dead Sea fruit, a legendary fruit which looked appetizing but turned to smoke and ashes when someone tried to eat it. The fruit is described in the Travels attributed to the 14th-century writer John de Mandeville.

2004New Zealand Listener Sir Roger somehow morphs into a sort of bad teddy bear, and Prince David's freedom and joy turn to ashes in his mouth.