Gourmet food editor Melissa Roberts talks about key limes here. Key limes are much smaller than the conventional limes that you usually see at supermarkets. When they go out of season they become a little dry, their peak season being spring. They're picked off trees when they're dark-green but they're not ripe yet, they are ripe when they become pale green. As they are so small it can be tricky juicing them. A reamer can be used but it is better to use a citrus squeezer, there is a smaller one made especially for key limes. Put the key lime face down into the open citrus squeezer with its holes facing towards a bowl, now just give it a gentle squeeze and that's it. If you don't have a citrus squeezer then you can just use a fork. Stick the fork into the fruit and just squeeze it with your hands. Now you know how to juice a key lime.