Two causes, and they taste slightly different.
Overheating
The common one. Milk tastes sweeter as it warms up to about 65 °C (149 °F), then turns. Past roughly 70 °C (158 °F) the lactose degrades and the proteins denature further, and the flavor goes flat, cooked and faintly sulfurous. People describe it as burnt, though nothing has actually burned.
The fix is to stop earlier than feels right. Hand on the side of the pitcher, stop when it becomes uncomfortable to hold. That is about 60 to 65 °C (140 to 149 °F) and it will feel cooler than you expect if you are used to overheated milk.
Plant milks turn earlier still — stop around 55 to 60 °C (131 to 140 °F).
A dirty steam wand
The one people miss. When steam stops, the pressure drop draws milk back up into the wand as it cools. That milk sits there, warm, until the next use, when it is blown into your fresh pitcher.
The taste is sour and stale rather than cooked, though people often report it as burnt.
The fix takes five seconds: purge the wand for a second and wipe it immediately after every use, while the milk is still wet. Baked-on milk is far harder to remove than fresh.
The eggy note
Whey proteins, beta-lactoglobulin in particular, carry sulfur-bearing amino acids. Above about 70 °C (158 °F) they denature and release hydrogen sulfide and related compounds, the same smell as cooked egg; above 75 °C (167 °F) the milk is clearly eggy and will no longer foam. The reaction is irreversible. Preheating the cup, not hotter milk, is how to serve a hotter drink.
Actual scorching
On machines with a heating element in direct contact with the milk — cheap frothers rather than steam wands — milk really can scorch onto the hot metal. That is a design problem, and it is why induction frothers and non-stick pitchers exist.
If it tastes burnt from the first sip and you did everything right
Check the coffee. An over-extracted, bitter shot can read as burnt through the milk, and people blame the milk because it is the last thing they touched.
What people want to know
How do I clean the inside of the wand?
Purging after each use handles most of it. Once a week, soak the tip in a milk-system cleaner and purge again — most machines let you remove the tip for a proper soak.
Does the machine matter?
Somewhat. Very powerful steam heats fast and leaves less margin for error, which is why cheaper machines with weak steam are paradoxically easier to avoid overheating on.
Last reviewed 30 October 2026