When juicing grapefruit, lemons, limes or oranges by hand, it can be a little tricky squeezing out all the juice, as a little elbow grease can only get you so far. So what can you do to get extra juice out of your citrus fruits? Microwave them for 15-20 seconds, or just until warm. Microwaving heats the cellulose and pectin contained in a fruit’s cavities, which weakens their hold on the actual juice. Furthermore, the natural sugars contained in fruit juice have a lowered viscosity when heated, allowing it to flow more freely.
Based on personal experience, I have been able to get up to an additional tablespoon juice out of a whole lemon after microwaving. Results, however, vary depending on the size and type of fruit you are juicing.