Pho broth is a clear, deeply aromatic beef or chicken broth built through charring aromatics, long simmering of bones, and careful skimming. Unlike French stock which achieves depth through mirepoix and reduction, pho broth achieves complexity through char-roasted onion and ginger, toasted whole spices, and fish sauce. The broth must be simultaneously deeply flavoured and crystal clear — a paradox achieved only through patient skimming and gentle simmering.
Bones are blanched first (boiled 10 minutes, drained, rinsed) to remove impurities. Onion and ginger are charred directly over flame or under broiler until blackened — this provides the smoky-sweet backbone. Star anise, cinnamon, cloves, coriander seeds, and cardamom are toasted in a dry pan. Everything simmers together for 6-8 hours (beef) or 2-3 hours (chicken) at the gentlest possible simmer — barely a bubble breaking the surface. Skimming fat and scum is continuous. Fish sauce and rock sugar are added near the end for seasoning.
The char on the onion and ginger should be extensive — nearly completely blackened. This provides the signature smoky depth that distinguishes pho broth from all other beef soups. If broth is cloudy, strain through cheesecloth. For pho bo (beef): use a mix of leg bones (collagen for body), oxtail (flavour), and marrow bones (richness). The moment of assembly matters: scalding broth poured over room-temperature noodles and raw-sliced beef — the broth cooks the beef at the table.
Boiling the broth — turbulence emulsifies fat into the liquid, making it cloudy. Not blanching bones first. Not charring onion and ginger dark enough — black is correct, not just brown. Using ground spices instead of whole — they cloud the broth. Over-spicing — star anise especially can overwhelm. Not skimming frequently.