Milk and Milk Products Technology

EVAPORATED MILK

Flow diagram andmanufacture

Filtration/clarification

• Thisis done in order to remove the visible foreign matter at a temperature of 35-40ºC, and then cooled.

Standardization

Standardization of the raw milk is carried outin 3 stages,

• For desired fat/SNF ratio, (usually 1:2.44, donein raw milk)
• Desired ratio of added sugar to the total milksolids (done prior to condensing)
• To adjust the concentration of the finished product to the required total solids content (after finishing the batch, i.e.,prior to homogenization).

Forewarming/Pre-heating

• Which is done for making the finished product free from microorganisms and enzymes,to ensure uninterrupted boiling in pan and to control age thickening in the finished product. The time temperature combination varies over 82-93ºC for 5-15 minutes or 115 –118ºC for no hold. Tubular heat-exchangers are commonly used.

Evaporation

• Evaporation means the concentration of milk orliquid products: the water has to reach a boiling point: and the steam musthave a pressure equivalent to ambient pressure. Vapour (steam) is removed by the pressure difference. No sugar is addedhere and normally a continuous operation takes place. It is customary to slightly over-condense themilk to facilitate standardization later.

Homogenization

• After evaporation and before cooling, theevaporated milk is thoroughly homogenized to obtain a uniform fat emulsion andreduce separation of fat to a minimum during storage. The temperature is usually 49 ºC as the product is removed from the last part of the evaporator. Two-stage homogenization is generallyrecommended, 2000 psi in the first stage and 500-psi in the second stage. After which the samples are cooled to 7 ºCand stored.

Pilot sterilization test

• Purpose to determine the amount of chemical stabilizers (trisodium citrate or disodiumphosphate) to be added to any given batch of evaporated milk for the mostsatisfactory heat stability.
• An approximate 10 percent solution of stabilizer is prepared for use, so that0.1ml of the solution is equivalent to the addition of 1 g of dry salt forevery 16 kg of evaporated milk.
• Theamount of stabilizers to be added to any batch is determined by trial. The sample cans containing measured amount of stabilizer solution and a fixed quantity of evaporated milk are sterilized at117 ºC for 15 minutes and then cooled rapidly to 24 ºC. As soon as they have been cooled the cans are opened, examined for smoothness and colour and testedfor viscosity. According to Mojonnierand Troy, aviscosity of 150ºR on the Mojonnier-Doolittle viscosimeter represents thecorrect viscosity of evaporated milk as it comes out of the sterilizer.
• Ifthe viscosity tests for pilot sterilized can show that no stability correctionis necessary, the batch is ready to be filled into the cans. However if the tests show otherwise,stability corrections becomes necessary.
• Basedon the pilot sterilization test, the calculated quantity of stabilizer should be added to the evaporated milk in the form of a solution using just enoughwater to dissolve it.

Packaging

• The cans are now mechanically filled withvolumetric fillers, the types of one used for this purpose are the sanitarycan, the can with a solder seal, and the vent hole can. The temperature of evaporated milk whenfilling the cans should be neither high nor low, but around 5 ºC; a higher temperature cause foaming; while a lower temperature increases the tendency towards ‘flipping’. This refers to the sudden snapping of can ends from their slightly concave contour to a convex outward bulge, which is usually accompanied by an audible sound. The cans should be filled as nearly full aspossible.

Sterilization

• Immediately after sealing and beforesterilization, each can is tested by means of a dependable leak checker /detector, where the cans pass submerged in a hot-water bath. In case of leaky cans, air bubbles rise tothe top: these cans are removed for repair. The filled and sealed cans, which have passed the test for leaks, arenow ready for sterilization. The purpose of sterilization is to destroy all germ life and enzymes present, thereby preserving the product permanently. During sterilization, the temperature is raised to 116-118 ºC and held at this temperature for 15 minutes. If the cans cannot be sterilized within an hour or two, they should be then held under refrigeration.

Batch method

• This consists of a water steam boiler-like, horizontal steam drum, with hollow interior having a revolving frame, in which the cans are loaded. The sterilizer rotates at 6-12 rpm, withuniform distribution of heat.

Continuous

• Here the cans are progressively heated to a few degrees below the boiling point, andfinally enter the sterilizing area proper. Later cooling process starts withthe cans gradually moving through progressively less hot-water chambers andfinally through cold water.

Cooling

• Immediatelyafter holding time is over, the evaporated milk is cooled within 15 minutes to 27-32ºC. Rapid and uniform cooling is important. Bulging of the cans can be avoided by usingcold water and in continuous system, cooler operates at 10 psi.

Shaking

• Thisis done to break mechanically, any curd, which might have formed during theprocess of sterilization to a homogenous smooth consistency.

Storage

• Thoughevaporated milk can be stored at room temperatures, a storage temperature of5-16 ºC is generally used, which helps to keep the product acceptable even upto 2 years. Inversion of cans once in3-6 months during storage will help to minimize fat separation.