I've read recently some articles about English toffee candy and the issue of butter separation was mentioned there.
I am looking for further information abut this phenomenon (what causes this separation of butter from the candy during cooking) and how can one prevent the separation besides using an emulsifier (like lecithin).
Someone has mentioned that salt has a stabilizing effect on the emulsion, is it true?
Butter separation doesn't only refer to the butter separating from the toffee (sugar), butter is make of milk fat rendered and the milk solids, when butter separates this is due to these parts separating. This is the fat that you see on the toffee, this usually comes from the components cooling at different speeds.
As with anything that you are making using melted butter, like a hollandaise sauce, adding a spoon or two of very hot water and agitating helps with the dispersion of both the fats and the heat. Stirring is an important component to ensure the heat is equally distributed throughout the mixture.
Thanks to @Aaronut for correcting the language!
Pertaining to salt acting as a "stabilizer", I have this experience to offer - I never had a significant issue dissolving the sugar into the butter (first step), until I switched from salted butter to unsalted - suddenly I had water that could not be eliminated. Some advise that adding 1/8 to 1/4 tsp salt per 4oz will rectify this, but I found this not to be true in two attempts. When I switched back to salted butter, this frustrating problem went away.
