Because of their thick skins, any brown marks or scratches don’t necessarily affect the quality. Choose ‘heavy’ fruit and avoid any with wrinkly skin or soft spots at the stem end.
For the juiciest grapefruit, store at room temperature for up to one week. If you want to keep them for 2 to 3 weeks, then rather refrigerate.
Freshly squeezed grapefruit juice, if stored covered in a refrigerator, will retain 98% of its vitamin C for up to a week.