How mustard is made

The heat in mustard does not exist until water touches the ground seed and two compounds meet.

stations: 6
things upstream: 30
raw sources: 15
steps from the ground: 7

The short version

Yellow mustard seed is soaked for about two days to soften its hulls, then milled and ground again to remove hard pieces. Mixed with vinegar, water, salt and turmeric, it runs through mills that make the slurry thicker with each pass. Most big producers now use heat to speed things up. Raye's in Maine still ages it for weeks in barrels.

Soak the seed

Yellow seeds sit in water for about two days so the hulls break down. Many commercial makers skip this and buy already processed mustard powder.

Goes in
Mustard seed Water
Mill off the hulls

Milling breaks each soaked seed into tiny pieces and separates it from its hull. A further grind takes out any hard fragments that got through.
Mix the slurry

Crushed seed joins water, distilled vinegar and salt in a large container. Turmeric goes in for the yellow color.

Goes in
Vinegar Table salt
Run through the stones

At Raye's in Eastport, Maine, the slurry passes through sets of quartz millstones dating to 1900, growing smoother and thicker each time. Cold well water protects the flavor. Most commercial plants use heat instead, for speed and yield.
Age the paste

The mustard rests for a few weeks before packing, which takes away some of the bite.
Fill jars and bottles

The finished paste is filled into containers and labeled. At Raye's this still happens two jars at a time.

Goes in
Glass jar

End of the lineMustard Next it goes into mayonnaise.

Worth repeating

The oldest known evidence of humans eating mustard is a seed cake from Syria dated to between 9224 and 8753 BC.
The word mustard comes from the Latin mustum, because the Romans mixed ground seed with grape must.
Mustard can act as an emulsifier and keep Hollandaise from curdling.