Coffee is acidic. It will curdle regular cream on occasion. The hotter it is , the more likely it will curdle. The older the cream/half 'n' half, also the more likely it will curdle. I beleive that cream that is intended for coffee (like the little cups of it in restaurants) have an additive that prevents curdling which is missing in cream that's sold in pints. Likely, that's also the difference between regular soy milk and soy creamer.