are oil and water so difficult to mixand how does adding an
egg yolk help?
molecules like to stick together. Thats why water drops bead
up when you spray them on a waxy surfaceand its also
why oil and water dont mix.
molecules stick together because of their chemical structure. Each
water molecule is made up of two hydrogen atoms and an oxygen atom.
(Thats why water is sometimes called H2O.)
Each hydrogen atom is made of a positively charged proton and an
negatively charged electron. Within the molecule, the hydrogen atoms
form bonds with the oxygen atom by sharing their electrons. But
the oxygen atom tends to hog the negatively charged electrons, becoming
negatively charged and leaving the hydrogen atoms positively charged.
like water, which have some areas that are positively charged and
some that are negatively charged, are called polar molecules.
Polar molecules tend to attract other polar molecules. The positively
charged area on one molecule will attract the negatively charged
area on another, pulling the molecules together.
molecules that make up fats and oils are nonpolar molecules.
In these molecules, the electrical charge is evenly distributed.
Because polar water molecules like to crowd together, they tend
to push out any nonpolar oil molecules. And the oil molecules have
an affinity for each other as well.
stirring or shaking can temporarily mix oil and water, a substance
known as an emulsifier is needed to stabilize this state
of affairs. One end of an emulsifier doesnt like water and
will become embedded in a drop of oil, while its other, water-loving
end, sticks out into the water and prevents the oil droplets from
merging together, creating an emulsion. In addition to proteins
that can act as emulsifying agents, egg yolk contains an abundance
of lecithin, a fatlike molecule known as a phospholipid.
more information about emulsions, click
the labels of many foods, you will find the ingredients lecithin
and soy lecithin. Lecithin extracted from soybeans is used as an
emulsifier in many food products.
molecules can also serve this function. Detergent cleans your greasy
dishes because each detergent molecule has one end that attracts
oil and one end that attracts water. The detergent molecules stick
to the oil and lift it off the dishes.
Why does the kind of saucepan matter?
you use an aluminum or iron saucepan, metal oxides can discolor
the lovely yellow of your sauce.
do I have to keep the heat low?
their natural state, egg proteins are long molecules that are all
curled up into a ball. When you heat them, these proteins uncurl
and form bonds with other proteins.
you are cooking the egg yolks for hollandaise sauce, you want to
heat them enough to cause the proteins to uncoilbut not so
much that they form many bonds with other proteins. The hotter you
get the proteins, the more they are likely to bond to other proteins.
Heat the yolks too much, and youll end up with scrambled eggs!
do I have to keep whisking? Why cant I just dump all the butter
in at once?
keep whisking the mixture as you add the melted butter because you
want to break it up into tiny, tiny drops. Each tiny drop ends up
surrounded by emulsifiers. But to give the
emulsifiers a helping hand, you need to keep the butter from gathering
in a big glob. You do that by constantly whisking while you add
the butter, and by adding the butter slowly.
curdled hollandaise sauce be saved?
broken emulsion isnt a complete disaster. Providing you havent
overcooked the egg yolks, it can be formed again. Simply whisk the
broken hollandaise gradually into another beaten egg yolk. Then
serve it immediately. It wont be quite as delicate, but most
guests are so impressed with homemade hollandaise, they probably
try to store this sauce, as its the ideal medium for bacterial
growth. And because oil and water expand at different rates, extremes
in temperature also cause hollandaise to separate. Refrigeration
doesn't work. The butter solidifies and separates. And reheating
causes curdling. Once youve made hollandaise sauce, serve
it as quickly as possible.”
Gardiner and Sue Wilson, The