The coffee pours out of the truck into the red box at their feet, when it’s full they open a trap door on the bottom and count another box full. The guy on the right is measuring out one liter of beans for quality control. They count the number of red beans (higher quality) and number of green beans (lower quality) to determine the quality. They add them together to get a total that indicates size. The price paid is based on the size and ratio of red to green.