I have a culinary physics question. A Butterscotch recipe that I make a lot requires 1 cup of white sugar, 1 cup brown sugar, 1 cup water, 1/4 cup corn syrup, and 1/3 cup butter. Heat all except the butter in a large pot, stirring until dissolved and then not stirring to 250 degrees. Add butter and cook to 280-300 degrees (hotter makes it more brittle). Pour out onto a greased tray.
Not bad - try it! However, my question is why does it want to boil over so much more easily if I use dark brown sugar vs. light brown sugar? Even with light brown sugar I have to keep an eye on it, but if I use dark brown the boiling mixture almost looks like it is “foaming” and I have to heat it VERY slowly to keep it from boiling over. At least I only need to fight with it until it’s time to put the butter in; that stops the “foaming” and I can relax until it finishes cooking.
So, what is the likely reason dark brown sugar gives me so much more difficulty keeping the boiling under control than light brown sugar?
The only difference between white sugar and brown sugar is the addition of molasses and the percentage of molasses determines whether it is light or dark brown. My guess is that the dark brown has more water (molasses being hygroscopic) and as the water boils out it is causing the foaming.
Whether you’re using real brown sugar or the brown sugar most people use, the difference is indeed in the molasses content. Both light and dark brown have a fairly high moisture content as well.
I’d recommend you use real (less refined) brown sugar, rather than white sugar that’s been re-blended with the molasses originally extracted from it. I don’t see the point to it, it isn’t as healthy (unrefined sugar still contains some vitamins and minerals; white sucrose has none), and I think natural brown sugar tastes much better.
Less refined dark brown is sold as Muscovado sugar, light brown as Demerara. Be sure you read the packaging to make sure you’re getting natural/raw/unrefined/less refined sugar (different manufacturers use different terms). Billington’s is the brand I normally buy.
I would suggest the higher molasses content makes the mixture more viscous, and thus more likely to foam (since it traps bubbles more efficiently). Adding the butter not only cools it but lowers the viscosity.
I’ve found dark brown sugar works better in glazes and generally won’t char as readily as the lighter stuff. However, I’m sure by controlling the amount and other ingredients light brown sugar could work just as well.