The spoon or other dulled steel sinkers is the norm for sinking large pieces of food. There's a corkscrew-looking device on the market that does the same as a spoon but, it's no improvement. Some wedged hard fruits can be nuked for 15-30 seconds, in a bowl of water, to expand and release enough trapped air/gas in the tissues to make them negatively buoyant (Yes, ...fruits breath).