I recommend watching Egg Files VII - Good Eats. It is an entire episode on meringue.
Important factors affecting the result:
- amount of sugar
- how the sugar is incorporated
Alton Brown explains how to make three types of meringue: french, italian, and, swiss.
Here are a tidbits of info from that episode:
- add pinch of salt to egg whites
- whip egg whites,
- add sugar slowly until dissolved
- add vanilla extract
- add cornstarch and vinegar
- bake, then turn off oven and wait 3 hours with oven door ajar
low temperature 250 degrees fahrenheit
The low temperature means the meringue dries out slowly.
The outside becomes dry (crisp) first, and since the
temperature is dropped before water inside can escape
the inside becomes soft and moist.
The acid from the vinegar helps the structure of the foam (note: new eggs
are slightly acidic, so use new eggs for meringue).
The corn starch prevents any liquids from seeping out.
These meringues becomes very gooey inside.
Note: Hot water can dissolve more sugar than cold water.
Sugar keeps water in the final product.
- whip egg whites with a litle salt and vanilla extract
- make hot sugar syrup with sugar and corn syrup
- slowly drizzle syrup into foam while mixing