Used coffee grounds

Used coffee grounds are the solid residue left behind after brewing coffee, and although usually thrown away they still contain sugars, proteins, lipids and minerals such as potassium and nitrogen. They are commonly reused in gardening as compost or mulch that slowly releases nitrogen into soil, particularly for acid-loving plants, and as a growing substrate for oyster mushrooms without needing pretreatment. Industrially they can be processed into bioethanol, biodiesel or biogas, mixed into concrete as a partial sand replacement, or used in cosmetics, body scrubs and sound-absorbing panels. Worldwide, coffee brewing generates more than fifteen million tonnes of spent grounds a year, making their reuse a significant area of ongoing research.