Evaporated milk, also known as unsweetened condensed milk or dehydrated milk, is a form of concentrated milk with a larger shelf life than regular milk.
Unsweetened condensed milk has about 60% of the water removed from it. After the water is removed, the liquid that remains is cooled, sterilized at high heat (around 240° F), and then canned. The heating process gives evaporated milk a darker color and a slightly sweeter, caramel-like taste. Evaporated milk also has a higher concentration of nutrients and energy. This means that one cup of evaporated milk will have more nutrients and provide more energy than one cup of fresh milk. Vitamin D is also usually added to boost the nutritional value of evaporated milk.
The unsweetened condensed milk can be made from whole milk, skim milk or recombined milk with the skim milk powder, anhydrous milk fat (AMF) and water.
Following steps are followed to manufacture Unsweetened Condensed Milk.
- Reception of milk and testing: The raw milk is transported from the dairy farm to the plant in refrigerated tank trucks. The milk is tested for odor, taste, bacteria, sediment, and the composition of milk protein and milk fat at the plant.
- Standardization: In this fat and solids not fat (SNF) has been adjusted to a predetermined level. The composition of evaporated low-fat milk is 7.5%–9.0% fat and 18%–22% non-fat milk solids.
- Preheating/Pasteurization: To improve the concentrated product’s heat stability and impart optimum viscosity to the finished product, the fluid milk is preheated before it is condensed.
- Evaporator: Water is evaporated, employing indirect heating. Product and heating medium (steam) are kept separate from one another utilizing a special steel sheet, to minimize the thermal impact on the products from the heat applied, evaporation takes place in a vacuum at pressures of 160 – 320 hPa, equivalent to water boiling temperatures of 55°C – 70 °C. In milk Industry, generally, three types of evaporators are used- Falling film evaporators, Rising Film Evaporators, Circulation / vertical Evaporators, Horizontal Tubes Evaporator, explained below.
- Multiple-effect Evaporator: A multiple-effect evaporator, is an apparatus for efficiently using the heat from steam to evaporate water. In a multiple-effect evaporator, water is boiled in a sequence of vessels. If two evaporators are connected in series, the second effect can operate at a higher vacuum (and therefore at a lower temperature) than the first. Thus the vapour evolved from the product in the first effect can be used as the heating medium for the next effect, which operates at a lower boiling temperature due to the higher vacuum.
- Falling film evaporators: A falling film evaporator (FFE) is a specific type of vertically oriented shell and tube (S&T) heat exchanger used to separate two or more substances with different boiling point temperatures. The liquid to be concentrated is supplied to the top of the heating tubes and distributed in such a way as to flow down the inside of the tube walls as a thin film. The liquid film starts to boil due to the external heating of the heating tubes and is partially evaporated as a result. The downward flow, caused initially by gravity, is enhanced by the parallel, downward flow of the vapor formed. Residual film liquid and vapor is separated in the lower part of the calandria and in the downstream centrifugal droplet separator.
Difference between Rising Film Evaporator
- Homogenization: Homogenization is a mechanical treatment of the fat globules in milk brought about by-passing milk under high pressure through a tiny orifice, which results in a decrease in the average diameter and an increase in number and surface area, of the fat globules. It is done to create a stable emulsion where the fat globules do not rise to form a cream layer.
- Cooling: After homogenization, the pre-treated milk is cooled to about 14 °C to send for further processing.
- Canning: Canning machines for condensed milk automatically fill and seal the cans before sterilization.
- Sterilization: Done in two ways i.e.
(a) Continuous Autoclave – In the continuous autoclave, the cans pass through on a conveyor belt at a precisely controlled speed.
(b) Batch Autoclave – In this the cans are first stacked in special crates, which are then stacked inside the autoclave.
- Storage: Once it is autoclaved, it is cooled to about 5°C and stored.
The process, as mentioned above was for retort processed unsweetened condensed milk. If the milk is to be condensed by UHT Processing, the above whole process remains same except point 7 and 8, which will be replaced by point 11 and 10 described below.
- UHT Treatment: The milk is pumped to the UHT plant/heat exchanger, where it is heated to 122°C –140 °C for a period ranging from 4 seconds to 2 minutes. Generally, a plate heat exchanger is preferred, and if UHT Treatment is used in the processing, than the preheating phase done in this case will below.
- Aseptic Filling: Aseptic processing and packaging is the filling of commercially-sterilized products into pre-sterilized containers.
Flow chart of Unsweetened Condensed milk:
When you see condensed milk can say that it is sweetened or not, be assured that it is sweetened. The most pronounced difference between condensed and evaporated milk is the absence of sugar or sweetener in the latter. Condensed milk will almost always be sweetened. Once the water is gotten rid of, the manufacturers use sugar to sweeten it. In case of unsweetened condensed milk, there is no addition of sugar in evaporated milk, and thus it is not sweeter to taste.