**3.2 Vacuum evaporation**

Vacuum evaporation consists of withdrawing water by applying energy in the form of heat to milk in a pressurized chamber that is lower than atmospheric pressure. This process promotes evaporation at temperatures between 40 and 75°C, which minimizes the changes caused to milk constituents due to heating. Downstream tubular evaporators are the most commonly used vacuum evaporators in dairy production. These can be coupled to systems as a finisher and flash cooler that finalize the concentration phase and rapidly cool the concentrated product [9].

*Dulce de Leche—Chemistry and Processing Technology DOI: http://dx.doi.org/10.5772/intechopen.82677* 

*Open-top dulce de leche pan.* 

### **Figure 3.**

*Diagram of a vacuum evaporator. C = evaporator calandria; S = liquid vapor separator; EF = effect; HTU = heat treatment unit; CT = cooling tower; CD = condenser; VP = vacuum pump.* 

The four main components of a vacuum evaporator are the evaporator calandria, the liquid vapor separator, the condenser, and the vacuum pump. The evaporator calandria and separator set is called the evaporation effect, so a machine that features five evaporator calandrias and five liquid vapor separators is a five-effect evaporator. **Figure 3** shows a diagram of a two-effect vacuum evaporator.

The evaporator calandria consists of a heat exchanger made up of tubes and an outer casing surrounding these tubes. The product to be concentrated is passed through the tubes while the heating medium is propelled (by steam or evaporation) inside the casing. An evaporator calandria's inner tubes transfer heat energy from the heating medium to the boiling product with the sole aim of promoting the passage of water from the liquid state to the gaseous state. The liquid vapor separators are directly connected to the evaporator calandrias and separate the concentrated product from the evaporated mass produced. The condenser, along with the vacuum pump, decreases pressure throughout the equipment.
