What you’ll need:
Fill the beaker with lemonade and pop the raisins in.
Raisins are denser than the lemonade, so initially they sink to the bottom of the glass.
Soon after the lemonade releases carbon dioxide bubbles. When these bubbles stick to the rough surface of a raisin, the raisin is lifted because of the increase in buoyancy. When the raisin reaches the surface, the bubbles pop, and the carbon dioxide gas escapes into the air.
The will cause the raisin to lose buoyancy and sink back to the bottom of the beaker. This rising and sinking of the raisins continues until most of the carbon dioxide has escaped, and the lemonade goes flat.
Give it a go and see the results for yourself!