Today I made an orange chiffon cake with buttercream frosting. I used Rose Levi Beranbaum's Classical buttercream recipe, in which 100 g of sugar and 90 g of water are cooked to a softball-stage syrup (114.5 Celsius) and then added to the yolks.
After making the cake batter, I had 50 g of just-squeezed orange juice left over. So instead of using 90 g water, I used 50 g of orange juice and 40 g of water for the syrup, hoping to have a more fruity flavor in the buttercream.
Shortly after passing 100 Celsius, the syrup started to foam, throwing very large and stable bubbles. I was very busy beating them back, using both my stirrer and blowing on them to pop them. But the foam still almost managed to climb out of the pot, it did form a heap above the upper wall level (the actual syrup only covered about 1-2 cm at the bottom of the small pot). I was also afraid that I will get an uneven heating, as the syrup forming the cell walls, with all the air inside, was probably not at the same temperature as the syrup puddle at the bottom.
The moment I took the syrup off the heat and poured into a cold cup, the foam disappeared completely.
Is that foam really a problem? Could it have ruined the syrup, or do I simply take a deeper pot and live with it?
Also, what caused the foam? Was it the orange juice, or can it happen without it too? If it happens without, what is the most likely trigger for it (I have made syrup before, and cannot remember such strong foam-building).
Regardless of whether it affects the end result, I found it difficult to work with. Is there something I can do to prevent it?