My wife says I have to cream butter and sugar with electric beaters in one direction only. She says this will help incorporate the air into the mix and make it creamy. I seem to be getting results moving the beater through the mix ad hoc. Is there any science to beating in one direction for the purposes of creaming butter?--Ling
Because of its complexity and the fact that cooking has evolved over thousands of years, it tends to be filled with both sound, provable science and popular folklore. For example, one similar "rule" is that you need to stir in one only direction when making a custard and that changing direction or whisking in a random pattern will cause the custard to curdle. I can say with certainty that the custard thing is false, because I never bother to stir in just one direction and my custards don't curdle.
I know of no science that would either support or disprove your wife's theory but looking over my various references, I can't find any that say creaming needs to be done by beating the ingredients in only one direction.
On the face of it, I also can't think of any good reason why it would be so. As I explained in the posting "Creaming Butter" the purpose of creaming is to incorporate air into the butter to help leaven the final product. According to Corriher, creaming is perhaps the most important step in making good cakes. Air bubbles are incorporated both from the air trapped between grains of sugar when mixing starts, and then by air blended in by the mechanical action. Neither of these would appear to depend on what direction the beaters move during blending. In fact, at the level of the beaters, regardless of how you move your hand, one blade is going clockwise while the other goes counterclockwise!
To test whether the direction of beating makes a difference, you would need to compare cakes made by creaming the butter by beating in only one direction versus cakes made when the beating is in random directions. You would need to be careful to control every other aspect of the cakes -- the ingredients would need to be accurately measured, the butter would need to be at the same temperature starting and ending, and the beating time would need to be the same duration. The cakes would then need to be cooled to the same temperature and under the same conditions.
After all of that, what I'm guessing you would learn is more likely that there are so many steps, involving so many factors, that ascribing differences in the result to the direction in which the butter is creamed is too simplistic.
The bottom line is that if your "ad hoc" beating technique produces good cakes, then you have shown that direction doesn't matter. Now, go and enjoy your cake.