About Homogenization

we are in the 46th class in Dairyand Food Process and Products Technology right, we had finished with standardization, butto have a little more. So, I am just showing it, I am not going throughit because now we will go to Milk Homogenization. And that is simply by mass balance, so bydoing mass balance you can also do this. And using the Pearson square which we havealready said earlier this is a more elaborative example of doing that Pearson square. How the Pearson square is being used thisis here been shown and some examples we have dealt with, and these examples you can alsowork out and do that right using the Pearson’s square technique also. Now, we come to homogenization, so this homogenizationis very very important step in milk because as we have said earlier also that milk docontain fat in different sizes right. So, ranging from say decimal micron to around25-30 microns this sizes are there and fat do have a common tendency to agglomerate.So, after agglomeration they became bigger sizes and from that they do come out to thesurface right this is by going we have said by Stokes law you can find out at what ratethis fat will get separated given a diameter right.So, to avoid that for a longer period to keep the milk for a longer period at no separationof fat. The next step pasteurization pasteurization you have killed all the pathogenic organisms.So, after that you need to homogenize, so homogenization is for the for the settlement;for the fixation of the fat content right. So, that fat content will not reduce becauseof separation to do that you need to do say homogenization.Now, homogenization is a physical process of breaking down the fat right, milk fat globulesinto tiny droplets small, small that will dictate at what may be 1 micron, may be 2micron, may be 3 micron. That size you will decide and to that allthe bigger sizes will be brought down of course, smaller sizes you cannot you cannot elevate,but the bigger ones will be brought down to the smaller ones to discourage cream separation;tiny droplets of fat do not rise in a milk column since reducing their sizes also increasestheir density in the milk. Because more the size bigger the size was there less homogenization of high pressure homogenization have been presentedover the years for and oil in water dispersion like milk where most of the droplets are lessthan 1 micron in diameter, two theories have survived. Together they give a good explanationof the influence of different parameters on the homogenizing affect.The theory of globule disruption by turbulent eddies that is micro whirls is based on thefact that a lot of small eddies, are created in a liquid travelling at a high velocityhigher velocity give the smaller radius. If any eddy hits an oil droplet of its own sizethe droplet will break up this theory predicts how the homogenizing effect varies with thehomogenizing pressure this relation has been shown in many investigation, the other oneis like this that the cavitation theory. Because more the size bigger the size was there less was thenumber now less is the size bigger will be their numbers. So, more fat dense will bethere in the particular or in a density in a particular one or uniformly it will be.A milk fat a milk homogenization is working at between 100 to 170 bars that splits allthe fat globules into very tiny droplets that increases the level of integration of thefat in the milk. As a result the milk fat remains on uniform or other milk firm, milkfat remains uniformly distributed in the milk right. Now, there is a heating section because milkhomogenization subsequently is seen that homogenization is also a function of temperature, the higherthe temperature better is the homogenization right. But there is also an optimum it isnot that it will go on increasing like this steadily right, it will not go on increasinglike this steadily that is also there that it will go like this it will be like this.So, there will be some optimum or maximum were the temperature is good.So, that is why it is that about 60 to 72 degree centigrade is effective to kill theClostridium botulinum spores. The steam exchanges the heat with the milk across the plate heatexchanger in a counter current motion at the same time at the end of this section. Thereis a temperature sensor which controls the flow diversion valve in a milk that does notattend the liquid temperature is diverted back to the heating section until it attainsthe required temperatures right. Once you got the temperature then holdingsection there is a after heating milk flows into the holding tubes, whose lengths havebeen have been calibrated with the milk flow rate to ensure that the milk takes at least16 seconds in the tubes, this holding time is 16 seconds in the tubes. All the milk mustremain in the required pasteurization temperatures at the end of the tubes. In case of breach,a sensor will trigger the floor diversion valve to take back the milk to the heatingsection to bring the milk to the required temperature.

This is microwave heating this will come afterwardsohmic heating we will come afterwards. So, high pressure processing will pass electricfield by non-conventional thermal, non thermal right, so while homogenization we do. That homogenization what it does pasteurizemilk around 100 to 125 atmosphere is allowed to pass through a homogenizing valve right.This homogenizing valve it does the homogenization right, as given in the next figure will showthe figure is like this let us go back to that figure which will be easier to understand. So, this is the fat globule, so there is ashear action that is happening like this and because of that the fat globule is gettingsay it is enlarged view like this they are getting segmented right and ultimately thisis becoming the intermediate become wavy and constrict right. So, this is the action ofthe force this becomes wavy and constrict and this disintegrate into the individualdroplets from this bigger droplet to the smaller ones they are getting by the shear action.So, this is splitting of globules by homogenization this mechanism follows right.So, now we go back to that, so that is what is happening in the in the homogenizationvalve that if the rate of shear is large globules are elongated, ripples are formed on theirsurface and finally, break into smaller sizes as we have shown in the next figure right,as milk flows out radially along the face say b b that is not we have not shown hereright. So, on the face of the valve the velocity reduces due to the increase in the cross sectionalarea right. Velocity is highest at point say ‘a’ dependingon the milk velocity at that point this will result in cavitation formation of cavitationand pressure of milk will increase as it moves radially outward from the centre of the valvethat is from the point ‘a’ to the point ‘b’. So, that if we can we can see ifwe can see this show radially here radially so; that means, it is going like this right.