⚙️ Homogenizer

A homogenizer is a machine that breaks up the fat globules in milk so the cream does not rise to the top. In essence, it is a powerful piston pump. It squeezes milk to 100–250 bar — 100–250 times normal air pressure — and forces it through a narrow gap about 0.1 mm wide. In the gap, the milk speeds up to hundreds of metres per second. The swirls at the exit tear the fat globules into tiny pieces.

The average globule size drops from about 3.5 micrometres to less than 1 micrometre. The milk must be hot for this, 55–80 °C: cold fat is partly solid and does not break up well. Many machines have two stages. The first breaks up the fat, and the second creates a little back pressure and separates globules that have clumped together. Almost all of the machine's energy turns into heat; less than 1% goes into the breaking up itself.

The homogenizer was invented by the Frenchman Auguste Gaulin. According to the Tetra Pak handbook, this happened in 1899, and the machine was shown to the public at the 1900 World's Fair in Paris. Today homogenizers stand in almost every dairy: on the lines for drinking milk, cream, yogurt and ice cream.