Wednesday, November 4, 2009

Rational behind pasteurization. Why it was a good idea 50 years ago and why it should be stopped

I believe that people try to make the best decisions they can with the information they have. From my previous post(s) you have picked up that I am think that milk should not be pasteurized. This is because it turns a health food into a death food. Well not quite death food, but no where near as nutritious as unpasteurized milk. I will post another day about why unpasteurized milk is more nutritious. However today I will discuss the history and information that drove the need for pasteurization. Like I opened with I believe that people made the best decision over 50 years ago to pasteurize milk. Once you know the reasons the decision was made we can then revisit the topic and determine if pasteurization is still necessary.

Bacteria/viral contamination of milk comes from two places. Firstly milk produced by the cow when she makes milk. If a cow has a virus it can find its way into the milk. This is nearly always due to a break down between the blood and milk barrier. I would be very surprised if the virus can migrate from the blood into the cell, and from the cell into the milk. It is for this reason that the WHO recommends that mothers with AIDS/HIV breast feed there infants. However if mum has mastitis, looks to wean baby, or has any other inflammation of the breast they need to immediately stop feeding baby. This is because these conditions cause break down in the milk blood barrier and allow the HIV virus into the milk. Due to this process cows milk could contain nasty viruses that the cow had. Have a look at the following graph, click it to make it bigger. It is about how long and how high the temperature needs to be to kill the common viruses found in milk. Take note the common viruses are tuberculosis (TB), diphtheria and typhoid.  These are very nasty viruses and we would associate these with the 3rd world / emerging nations. There is also the streptococci, which is a bacteria that gives you sore throats.

Given that there was no antibiotics and not cure for these things, if I was raising kids 100 years ago I would be championing for pasteurization as I would hate them to die from one of these infections.

 Well has anything changed over the last 100 years? Yes! Since early 20th century (eg before WWII) major advances in cow health have occurred. Firstly diphtheria and typhoid infections have disappeared, TB is massively reduced. Bacteriology can quickly determine types of infections and disease. Antibiotics and other interventions are now common place. Cows have much reduced bacterial infection rates thus reducing chance of any disease, if the cow has any, making it across into the milk.  

The second other source of contamination is from outside the cow, entering into the milk via the milking process or on its way to the consumer.An example is shown below. This shows a dairy that was infected with typhoid which caused a typhoid outbreak in  a city. This occurred due to the women who canned the milk worked a nurse, thus transferring the virus to the milk. Once this had stopped a typhoid stopped. So this was not some academic exercise, but a real problem.     

Another issue was the hygiene of the cows. Different pints (600ml) of milk were obtained from commercially available milk. They were then strained. Examples of the dirt and fecal matter are shown below. You can see that the amount of filth that was removed was up to 0.5 of a gram. This is up to 0.1% of the weight of the milk was the weight of the dirt, poo and god snows only what else!

How did this crud get into the milk. This fell of the cows udder, into the bucket, while being milked. Cows were often kept in atrocious conditions. The two photos below illustrate this. Although they are in black and white it shows how dirty the areas were. The outdoor pen where the cows would be kept and feed in is run down, muddy, rubbish and curd everywhere. The cows in this place would have been filthy as they often would have there udders on the ground. Firstly from laid down to chew their cud and rest. Secondly when it got muddy there feet would sink into the mud thus lowering the udder allowing it to scrap along the dirt. A photo of the inside of a area such is this is shown. See the cobwebs, dirt, the complete lack of cleanliness is continued inside the barn.  

If my milk came from such a place as this I would want it pasteurized! However such places have been outlawed. Since these photos were taken about a century ago hygiene standards on farms have massively increased. Thus contamination in raw milk has massively decreased.  

Thus pasteurization was solution to a hygiene problem. They took a two pronged approach. One was to pasteurized and the other was to clean up the farms. Now the farms are healthier (and if they shipped raw milk the farms would have to be an even higher standard) we on longer need to pasteurize the milk and destroy a lot of its nutritional value.

Graphics from Boyd Preventive medicine 6th ed. Saunders (c) 1920 - 1942. Used by kind permission of Boyd family.

No comments:

Post a Comment