**4. Dulce de leche manufacturing processes**

DL can be produced in four ways:

a.Manually

b.Open-top pan

c. Split addition of the mixture to the open-top pan

d.Preconcentration in vacuum evaporator and termination in open-top pan

We will address the latter three processes because they represent the bulk of DL production in Brazil. DL-processing technology consists of the evaporation of water by indirect application of heat in equipment known as evaporators, or, more commonly, pans. The manufacturing process is shown in **Figure 4**.

The mixture of milk, sucrose, and other ingredients and additives is called the syrup. The DL syrup is subjected to continuous water evaporation by means of transferring heat energy indirectly using steam (pressure range: 100–600 kPa) from boilers. The vapor used becomes vapor condensate, water at 85–90°C, and the

**Figure 4.** 

*Dulce de leche (DL) manufacturing process diagram.* 

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

quantification of this makes it possible to determine the total mass of steam used in the manufacturing process.

 The water withdrawn in the gaseous state is called evaporated water and must be removed from the equipment rapidly to avoid condensation and reincorporation into the syrup. Hence, an exhaust fan system is required to remove the evaporate.

During evaporation, constant stirring is performed by mechanical agitators at a speed of 72 and 80 rpm. This stirring is necessary to minimize deposit formation on the heat exchanger equipment walls. Processing time may vary from 30 minutes to 4 hours, depending on heat, exchange area, milk volume, and steam pressure used.

Color, flavor, and viscosity of the dulce de leche are directly related to its processing time, which ultimately determines the characteristics of the final product. DLs produced in a very short time have a pale color, a less pronounced flavor, and a low viscosity.

The most common heat exchanger used to produce dulce de leche is a pan made of an inner stainless steel wall and an outer wall that allows steam to enter and circulate between the two. The working capacity of pans varies from 25 to 1500 L of syrup (**Figure 5**).

 In most cases, the evaporation phase is started when all milk and sugar are added at the beginning of the process, though in some factories, only some of the milk and sugar are used at the beginning of the process and the rest is gradually added throughout (split addition of the mixture to the open-top pan). This second method allows a higher quantity of syrup to be processed than that which volume capacity of the pan would ordinarily allow, as shown in **Figure 6**. An additional advantage of this type of technology is related to reduction on process time as a consequence of a higher pressure in the heating medium during evaporation. The higher solid content in the syrup during evaporation process leads to boiling over reduction (**Figure 7**).

**Figure 5.**  *Open-top pan manufacturing process.* 

**Figure 6.**  *Split mixture addition to an open-top pan.* 

**Figure 7.**  *Split addition of the mixture processing in an open-top pan.* 

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

In large-scale productions, the volume of milk to be evaporated exceeds 30,000 kg of milk per day; it is common to use vacuum evaporators in the preconcentration stage of the fluid milk, with the objective of lower energy waste (preconcentration in vacuum evaporator and termination in open-top pan). As shown in **Figure 8**, DL can be obtained using vacuum evaporators combined with open-top pan.

 The vacuum evaporator considerably reduces steam consumption in the industrial manufacturing settings and increases production capacity. While an open pan uses approximately 1.1–1.3 kg of steam to evaporate 1.0 kg of milk water, an evaporator requires only 0.1–0.3 kg of steam to evaporate the same amount of water. The disadvantage of the vacuum evaporator is that it cannot be used as the sole equipment to produce dulce de leche because it does not allow the necessary physicochemical modifications in the syrup. Thus, the process calls for concentrating the milk and sugar syrup under vacuum conditions of 62–66°Brix, and then the syrup is concentrated in an open-top pan for another 20–40 minutes so that it can achieve the viscosity and color required to meet desired standards (**Figure 9**).

 Concentration in multistage evaporators is common in dairy plants that process milk powder, sweetened condensed milk, and evaporated milk. However, due to the high initial cost of equipment, these evaporators are only feasible in companies that process large volumes of milk. An evaporator is a device that works with a partial vacuum in order to lower the boiling temperature. Thus, the effects of heat on the milk protein structure and lactose caramelization are minimized. Each stage is actually an evaporator, but all stages subsequent to the first use the steam released from the precedent stage as a thermal source. In the multieffects system, the steam generated in the first stage and the partially concentrated liquid flow into the vapor separator where they are separated by centrifugal force; the pressurized product is then forced into the vaporization chamber of the next stage, while the vapor is also pushed into the evaporator calandria where it is condensed by yielding energy in the form of heat to the liquid to concentrate.

**Figure 8.** 

*DL processing with preconcentration in a vacuum evaporator and final phase in an open-top pan.* 

Falling film evaporators fitted with a top feed that use gravity to draw the liquid down before it enters centrifuge stage in heated tubes are the most common evaporators used to make dulce de leche. Plate evaporators have also been used; these concentrate the milk quickly, which saves saving time, steam, and labor during processing.

Multistage evaporator concentration occurs at low temperatures (compared to the conventional open-top process) of 70–48°C. Therefore, neither the Maillard reaction nor a substantial increase in product viscosity (fundamental characteristics in DL have a chance to develop). This makes it necessary to finish processing in a conventional open-top pan to give the dulce de leche the desired organoleptic characteristics.
