This is a mere guideline. If you're not sure about this, but want to try it anyway, roast a small cantaloupe. If you're feeling a little more devil-may-care, roast a big one.
Many food professionals would have you, the home cook, believe that the culinary tricks they perform and the dishes they create in the kitchen are difficult. And it is true that some dishes are more suited to a professional kitchen than a home kitchen, but really what a chef has that most amateurs lack is exquisite, honed technical skills. From using a knife well to knowing which tools to use for any particular task, a chef is trained, either formally or from years of experience, to make complex dishes in a streamlined manner.
But the fact is that home cooks are perfectly capable of learning kitchen tricks, and it is our belief at the Joy Kitchen that home cooks are most in need of these tricks. Chefs need to know them because they have scores or hundreds of dishes to turn out every night. Home cooks need them because they have full-time jobs, kids, or any number of obligations to attend to and so cooking must usually be a hurried affair with little time for finessing finicky ingredients.
When I worked at the bakery, one of the tasks we all had to be fairly proficient at was separating eggs. We might separate sixty at a time to make pots de crème. Now that I'm mostly a home cook again, I still find myself needing to use this valuable skill. You can buy egg separators at any cookwares store, but this is a truly unnecessary tool that will simply take up drawer space and that you will only use sporadically at most. I prefer my hands.
Don't let anyone tell you that using your hands when cooking is a faux pas. Nothing is wrong with a pair of clean hands, and since it is the tool we are most familiar with, I highly encourage you to use them more often. You will feel more comfortable using them than some awkward tool, and they will be much easier to clean.
The first thing to do when separating eggs is to organize your workspace. I like to have my carton of eggs behind a row of three bowls. One bowl is for the whites, one is for the yolks, and one is to separate your eggs over in case the yolk breaks and you have to throw it out. Remember, when you are whipping egg whites there should be no trace of yolk or the whites won't stiffen properly. Having a safety net for those fragile yolks is essential. I also like to have a trash can at my side so I can throw the eggshells away immediately.
Now that you have your set-up ready, simply crack the egg gently against the countertop and break it open over your hand, cradling it loosely. Spread your fingers apart wide enough for the white to seep through them, but not wide enough for the yolk to fall through. If you notice that the yolk looks like it may be breaking open, simply close your fingers to prevent the yolk from blending into the whites. You may also find it simpler to transfer the egg carefully from one hand to the other, letting the white fall away as you keep the yolk in your hands. I have even witnessed a technique where the baker breaks multiple eggs (carefully) into one bowl and then pulls out the yolks, leaving the whites behind. This technique is best used when many eggs are being separated.
If you are preparing a recipe that calls for only egg yolks or egg whites and not both, there is no need to throw away the leftover egg components. Some ideas for leftover yolks: homemade pudding or custard, an addition to soups for a thicker texture, homemade mayonnaise, and hollandaise sauce. Some ideas for leftover whites: meringue cookies, meringue for a pie or for a pie “crust,” a healthier omlette or scrambled egg dish, and a binder for some cookies, such as amaretti (Italian almond cookies).
When a recipe calls for you to use both the egg yolks and the whites, but separately, you can count on a dessert with a light mouthfeel but a rich flavor. Incorporating beaten egg whites into a dessert will create a light texture, and using the yolks ensures that your dessert will hold together well (the protein in the yolks helps the flour, sugar, and fat to bind together) and also that your dish achieves the coveted rich taste that keeps people coming back for more.
My technique differs from the technique in the Joy of Cooking. As you can imagine, this poses a slight problem regarding which technique is the "correct" one. The primary reason I recommend using your hands is because I like being in touch (literally) with my food. I enjoy the act of using those tools most familiar to me--my hands--and am usually of the opinion that one more kitchen tool does not equal greater success in the kitchen. However, using your hands is not "technically" the most sanitary means of separating eggs. If you wash your hands well before and after handling eggs, there is no reason it should be any less sanitary than if you were to use a tool to help you. However, the sanctioned method for doing this, as written in the Joy of Cooking, is extra insurance against salmonella and should be considered as an option, especially when cooking for young children, pregnant women, the elderly, or those with weakened immune systems. This technique is quoted below.
Have 3 bowls ready. Holding an egg in one hand, tap the center of the side of the egg lightly yet sharply on a flat surface, such as the countertop, making an even break. Then hold the egg in both hands, with the break on the upper side. Hold it over the center of a small bowl and tip it so that the wider end is down. Hold the edges of the break with your thumbs, and widen the break by pulling the edges apart until the eggshell is broken in half. As you do this, some of the egg white will flow into the center bowl underneath, but the yolk and the rest of the egg white will remain in the lower half of the shell. Pour the remaining egg back and forth from one half-shell to the other, letting some more of the white flow into the bowl each time until only the yolk remains in the shell. Put the yolks in the bowl on the left and the whites in the bowl on the right.
As you perfect your egg separating skills, you will certainly find a method that you prefer, and it may or may not be one of the two mentioned above. The most important thing to keep in mind is sanitation. Make sure that your hands, work surface, and cooking tools are clean. The technique is up to you.