Spent 11 hours over 2 days trying to fix my royal icing, turns out it was the lemon juice
I was making decorated sugar cookies for my sister's baby shower in Sacramento last weekend and my royal icing kept drying with these ugly crater cracks on top, so I remade 4 batches and stayed up till 2am Saturday trying piping bags, different tips, and a new meringue powder brand. Finally my neighbor who used to run a bakery said to skip the lemon juice because the acid was messing with how it set, and a plain water batch dried smooth in 20 minutes. Has anyone else had royal icing crack because of one weird ingredient like that?
I read on a baking blog that acid in general messes with royal icing setting up right. The lady who wrote it said she tested batches with lemon juice, vinegar, and even a splash of orange juice, and all of them dried weird compared to just water. She said the acid slows down how the proteins in the egg whites firm up, so the top sets before the inside does and then it cracks. That matches what your neighbor told you about the bakery trick. Good to know it only took 20 minutes once you dropped the lemon.