Two related comments came in over the weekend in regard to sugar and soda. First this observation from reader Julie:
Another thought on the baking soda: milk heated with acid will curdle every time, and caramelized sugar becomes more acidic as it darkens. I like my caramel reasonably dark, so I’ve run into problems with curdling milk on more than one occaision. I find it also helps to use plain refined white sugar, as a blonde organic sugar (with a little residual molasses left in) will contribute to curdling.
Hey Julie! I’ve never had that happen when making caramel sauce (if that’s what you’re referring to here), but it makes sense. As you point out, dark caramels are acidic, as is molasses. Add heat and dairy and curdling is at least a possibility, especially as the caramel gets darker. Fat will help inhibit that protein bunching, however, so try cream instead or add some butter first. It’s a tough job but somebody’s gotta do it! 😉
Next we have this from reader Jen:
Joe, in making peanut brittle, the sugar syrup mixture turns from being translucent to totally opaque when the baking soda is added. I always find it absolutely fascinating to watch. I presume something similar happens in this recipe? Is that also part of the Maillard reaction or something else? The texture also changes in the peanut brittle because of the baking soda, from stretchy and, caramelly, to a very loose, egg white batter type consistency. Obviously that’s partly due to the foaming action, but is there anything else going on to cause that? And does that happen in this frosting too?
Hey Jen! What’s happening is a leavening reaction. Caramel, as mentioned above, is acidic. So when you add baking soda you get CO2 bubbles. It’s those bubbles that make the peanut brittle opaque, as light rays can no longer pass straight through the caramel. They get bounced around by the bubbles, so the brittle appears creamy.
However color isn’t the main reason most brittle recipes call for soda. It’s the texture change that’s the most important. All those bubbles turn the finished brittle into a foam, which makes it far easier to bite and chew compared to a straight caramel that’s had peanuts added. The bubbles make it both lighter and more rigid, so it shatters and crunches in the mouth…and sticks to teeth a whole lot less.
To answer the other part of your question, some browning reactions may well be occurring in there, since caramel holds heat quite well. Now that you mention it, I recall seeing some very blonde peanut brittle as well as some very dark peanut brittle, it probably has to do with the point at which the candy maker adds the soda. More heat will create more browning.
Lastly, I don’t think there’ll be any leavening reaction in the caramel cake icing. But then I’ll be adding an acidic caramel to a mixture that has baking soda in it…a little something may well go on in there. It hadn’t occurred to me until now, Jen. I’ll keep an eye out! Cheers and thanks for the great questions!