Question: why does beurre blanc split?
Answer: Normally oil and water don't mix. ... If you overheat a Beurre Blanc, the oil inside the fat globules will escape their protein/emulsifier cage and separate out. The good news is that if you allow the sauce to cool to about 110°F (43°C), and then add a small amount of water and whisk it in, the sauce will re-form.