The cool-down, and what goes in when

The cool-down is where the emulsion sets its final structure and where everything fragile is added. It is also where people often stop paying attention.

The most consequential ten minutes

The emulsion continues to build structure as it cools, so viscosity at 60 °C tells you very little about viscosity tomorrow. A batch that looks alarmingly thin while warm is frequently correct the next morning.

Keep mixing gently throughout. An emulsion left standing while still hot and mobile will cream before the structure sets, and that separation is built in rather than developing later.

Why cooling rate matters

Too fast and fats crystallize coarsely, which shows as graininess and as an emulsion with weaker structure. Too slow and everything sits at elevated temperature for longer, degrading actives and oxidizing the oil phase.

Consistent is more important than fast or slow. It is also one of the variables that changes silently when you scale up, because a larger batch cools more slowly by its nature.

What goes in and at what temperature

Everything heat-sensitive waits. In rough order as the batch cools: thickeners and any pH adjustment as it approaches warm, then preservative, then actives, then fragrance, each at or below the temperature its supplier specifies.

Those temperatures are published for a reason. A preservative added too hot can degrade, and a product with a degraded preservative reads as preserved on the label while being unpreserved in the jar.

Getting the order wrong

Adjusting pH after the preservative is in, rather than before, means the preservative may spend its life outside its active range. Adding an active above its stability temperature destroys the thing the product is sold on.

Write the addition sequence with a temperature against each line and treat it as part of the formula, because it is. Two people following the same ingredient list in a different order make two different products.

References