Do you taste food when you cook? Yes or no? You should definitely do this: the eye can be deceived, but the taste cannot be, and if a mistake been made, you may still have time to correct it. The proportion of 3-parts oil to 1-part vinegar for vinaigrette sauce is not set in stone, but is just a guideline. The main thing is to achieve the right balance of acidity, salinity and sweetness - this question will be answered by your taste. And the best way to taste the sauce is to dip a leaf of lettuce into it, shake off the excess and chew. It's better than tasting it when the salad is ready. Beat the sauce with a blender or a whisk, and if neither one nor the other are at hand, pour it into a bottle, close the lid, and shake well.