Why Apple Strudel Filling Turns Black

Question

Hello!
I make a Viennese-style apple strudel (stretched on table, unsweetened dough) with a cooked apple filling before baking.
I've made it several times, and the past couple of times I've made it, the apple filling has turned black after I add the nuts! (I've used 2 different kinds of nuts each time, same result - first time toasted pecans, second time toasted walnuts).
I cook the filling in a cast iron pan. (Ingredients = sliced apples w lemon juice & zest, butter, sugar (granulated & brown), cinnamon, vanilla paste (added after cooking/turned black), whiskey/brandy), once cooled I add the nuts).
What is the reason for the filling turning black?! It is somewhat alarming \looking\ but does not seem to affect the taste at all. I don't mind it because I made it myself and know what it is coming from, but I think others whom I serve it to are very turned off by the color. Please help!

Deb Steinfeld · Accepted Answer

Carly, thanks for your question. It is probably just a coincidence that it turns black when you add the nuts. The problem is most likely the cast iron pan. When you cook anything with acid (lemon juice and zest) in a cast iron pan there is a chemical reaction and the product can turn black as well as giving an irony taste. This doesn’t always happen so sometimes it has worked OK for you, others it hasn’t.
Try it again in a stainless steel pan and see what happens. You should get better results.
Also, I have made this style apple strudel with my own stretched dough without pre-cooking the apple filling (same ingredients) and it has worked just fine. You could also give that a try. I feel that while the apples do cook, it leaves them with a nice crunch.
Hope this helps.
Deb at Milk Street

Why Apple Strudel Filling Turns Black

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