How does C. S. Forester use imagery in Beat to Quarters?

Imagery:

"The coffee was a black extract of burnt bread, and all that could be said in its favour was that it was sweet and hot. The burgoo was a savoury mess of unspeakable appearance compounded of mashed biscuit crumbs and minced salt beef. Hornblower ate absent-mindedly. With his left hand he tapped a biscuit on the table so that the weevils would all be induced to have left it by the time he had finished his burgoo."