**3. Dulce de leche manufacturing technology**

 Originally hailing from Latin America, dulce de leche (DL) is one of the most widely manufactured dairy products in Brazil, where it is marketed as a paste or bar. Due to DL's low moisture content, the product can be safely stored at room temperature [8]. The primary ingredients used to manufacture DL are milk, sucrose, and an acidity reducer. Needless to say, the raw materials must be of good quality from reliable suppliers in order for the final product to have the desired characteristics. The milk used to make DL must be microbiologically safe (total bacteria count <300,000 cfu mL<sup>−</sup><sup>1</sup> in raw milk), remain stable during thermal processing, and preferably exhibit a high solid content (>11.4 g.100 g<sup>−</sup><sup>1</sup> of dry matter) [1].

Total processing time can vary from 40 minutes to 4 hours. Processing time depends on the type of equipment used and the amount of steam injected. Processing time plays an important role in a product's viscosity, color, and flavor and ultimately determines the characteristics of the final product [7].

 Processing end time for dulce de leche can be verified in two different ways: by determining the soluble solids content (above 66°Brix) or by observing how a small droplet of DL behaves when submerged in water. Once the desired solid content/ consistency is reached, the final product should be cooled to 75–80°C and then packaged while still warm in cans or glass containers that have been filled to the top to eliminate any air and prevent contamination. In general, the yield is 2.5 L/kg of DL. The product is then stored at room temperature for a period ranging from 160 to 180 days [8].

DL can either be handmade in batches or continuously produced in pans and vacuum evaporators or evaporators attached to pans. The pan used is generally a dual-ply container with a stainless steel interior and an outer wall, which lets steam pass between the two layers while also conducting heat [7].

### **3.1 Open top pan**

The technology used to manufacture dulce de leche is determined by the equipment used. Often, quality improvement is limited not by cost or lack of skills, but by the very equipment that is used to make the product.

 It is possible to make DL in 30 minutes or up to 6 hours using the same volume of milk. This shows how important equipment choice can be, since time factor can directly impact the competitiveness of a specific dairy plant.

 In the traditional manufacturing process (most common in Brazil), the milk and sugar mixture (syrup) is concentrated directly in double-walled stainless steel pans, through which steam flows. After the syrup has been prepared, gradual heating is applied to the liquid, which is continuously stirred. This stirring prevents the liquid in direct contact with the walls from scorching. Stirring also reduces foam formation, which allows water to evaporate more quickly from the syrup. Once the syrup reaches the desired consistency, the cooling process begins until the dulce de leche temperature has dropped to 75°C. The cooling step helps avoid high temperatures within the DL mass, which would otherwise affect the color and texture uniformity (**Figure 2**).

Primary components of an open-top dulce de leche pan:

