Emulsions: Mayonnaise and Pasta Salad

An emulsion is a mixture of substances that would not otherwise be soluble with each other.  In middle school chemistry we learned that "like dissolves like," meaning that polar substances will only dissolve with other polar substances because the intermolecular dipole-dipole partial positive and negative charges will attract one another.  Likewise, nonpolar substances have no permanent partial charges, so they do not attract polar particles but do disperse within each other quite nicely.  However, when we mix a polar substance, such as water, with a nonpolar substance, like oil, we find it impossible to integrate the two.

Incidentally, polarity arises from the differing electronegativity of elements.  Electronegativity is the tendency of an atom to pull electrons towards itself.  The smaller the atoms, and the more protons it has, the more strongly it can attract electrons becuase the positive protons in the nucleus are closer to the electrons, and there are more of them to create a n attractive force.  Following this trend, the most electronegative elements (such as Flourine, Nitrogen, and Oxygen) are located in the upper right side of the periodic table.  When these elements are bonded with a very weakly electronegative atom, the result is a tendency of the electrons to congregate by the electronegative element, creating a partial negative charge at that end of the particle and a partial positive charge at the other end.  This is a polar substance. If the atoms have similar electronegativities, no such grouping exists and the substance is nonpolar.

So how do we mix polar and nonpolar substances into an emulsions?  The answer lies in emulsifiers.  These tricky little molecules have both a polar end and a nonpolar end, so that they can dissolve both polar and nonpolar substances.  Mayonnaise, a common emulsion, is made possible by the emulsifyer mustard.  This was the emulsion we chose to attempt.

Ingredients
1 egg yolk*1/2 teaspoon fine salt1/2 teaspoon dry mustard2 pinches sugar2 teaspoons fresh squeezed lemon juice1 tablespoon white wine vinegar1 cup oil, safflower or cornDirectionsIn a glass bowl, whisk together egg yolk and dry ingredients. Combine lemon juice and vinegar in a separate bowl then thoroughly whisk half into the yolk mixture. Start whisking briskly, then start adding the oil a few drops at a time until the liquid seems to thicken and lighten a bit, (which means you've got an emulsion on your hands). Once you reach that point you can relax your arm a little (but just a little) and increase the oil flow to a constant (albeit thin) stream. Once half of the oil is in add the rest of the lemon juice mixture.
Continue whisking until all of the oil is incorporated. Leave at room temperature for 1 to 2 hours then refrigerate for up to 1 week.
* Raw Egg Warning
Read more at: http://www.foodnetwork.com/recipes/alton-brown/mayonnaise-recipe/index.html?oc=linkback

Troubleshooting common emulsions:

Troubleshooting Emulsion Sauces When an emulsion breaks, how you fix it depends on the sauce.
	Problem	Cause	Fix
MAYONNAISE	The mayonnaise fails to thicken.	The oil has been added too quickly, so it never gets dispersed.	Beat a fresh egg yolk with a tablespoon of water and/or lemon juice in a clean bowl, and slowly whisk in the broken sauce.
	The mayonnaise becomes oily on the surface.	Water has evaporated from the mixture, giving the oil droplets a chance to coalesce.	Whisk in a spoonful of water.
HOLLANDAISE	The sauce is lumpy and thin.	The egg yolk has overcooked.	Strain out the lumps and whisk the hot broken sauce into another gently heated egg yolk in a clean bowl.
	The sauce has separated while being kept warm.	The sauce has become too hot, causing the butterfat to leak.	Take it off the heat and whisk it vigorously, or briefly re-emulsify it in a blender.
VINAIGRETTE	The oil and vinegar have separated.	The simplest vinaigrettes do not contain emulsifiers like mustard, so the oil and vinegar separate unless they are being actively mixed.	Whisk the broken vinaigrette in a bowl or shake it vigorously in a closed jar and pour it over the food immediately, while it's still in motion. A separated mustard vinaigrette is fixed in the same way.
BEURRE BLANC	The sauce hasn't thickened.	The ratio of butter to liquid is too low. Either the vinegar mixture was not reduced enough before the butter was added, or not enough butter was added.	Add more butter.
	The sauce is creamy at first, but then suddenly thins.	The sauce has become too hot.	Because all of the elements to maintain an emulsion are still present, all you need to do is remove the sauce from the heat and whisk in ice chips, a few at a time, until the emulsion returns.