Vinaigrette turned watery?
Last night I made a vinaigrette with walnut oil, a bit of black truffle oil, red wine vinegar, a bit of dijon mustard and S&P. On assembly the texture had a nice viscosity, but I didn't use it to dress the salad until about a half hour later. By that time the dressing had become as thin as water, no amount of whisking would return it to a thicker texture that would cling to the leaves. Obviously next time I'll make the dressing at the very last minute, but I was topping the salad with poached eggs and wanted the eggs to be the last step. Has this happened to anyone else? Why did my vinaigrette become as thin as water?
What were your proportions of oil/vinegar/mustard? While mustard is great as an emulsifier, it doesn't hold an emulsification for long, it doesn't stabilize an oil/vinegar emulsion permanently. Assuming you had the correct proportions of ingredients, it's best to make a vinaigrette shortly before dressing the salad.
I have had this happen to me before and came up with a good solution. I put all of the ingredients into an empty jam jar ahead of time and let it sit until ready to dress the salad at which time I give the jar a vigorous shake to emulsify the dressing. Taste it before tossing the salad just in case the seasoning needs correcting. Seems to work well for basic vinegarettes. One of my go-to standards has 2 parts oil, 1 part yogurt, juice of a small orange, teaspoon of dijon mustard, teaspoon of honey, 1 part white balsamic or apple cider vinegar. Salt and pepper to taste. The addition of a bit of yogurt pretty much turns out a nice consistency every time.