Putting the squeeze on raw milk

Many of you will know that I have written several articles on the dangers of consuming raw milk.  In my opinion, any perceived benefits are greatly outweighed by the real risks.

However, if you will permit me to mix metaphors, you can now have your cake and eat it.

An Australian company, Made by Cow, is offering raw milk processed by "cold pressure".  There are few details available, but it appears that the company is using an established process (High Pressure Processing, HPP) to make the milk as safe as pasteurised milk.  The process has been approved by the New South Wales Food Authority, and the product can be sold in stores.

The concept of killing bacteria by applying high pressure has been known for many years, (Hite studied the effects of pressure on bacteria in 1899), but practical machines to process food have been difficult to build and the processes have all been slow.  

Pressures of up to 6800 Bar (about 100,000 psi) held for several minutes are required to kill bacteria. Of course, there are many possible combinations of pressure, temperature and time, and whether the pressure is applied in a single treatment or is cycled several times.  However, the degree of inactivation appears to depend on the duration of the high pressure, and not the number of cycles.

The primary site of damage to the bacterial cell appears to be the cell membrane.  If this membrane is damaged, its permeability may be greatly changed, resulting in failure of respiration and transport functions, and hence death of the cell.  Spores are very much more resistant, so milk processed by pressure alone is unlikely to be sterile.  There are some changes in foods resulting from HPP - some enzymes may be inactivated, while others have their activity enhanced.  Other effects seen in foods are the gelling of some non-enzyme proteins and enhanced browning reactions at high pressure.  One assumes that the Made by Cow patented process has overcome these undesirable changes in the milk.

The major problem with current HPP is that the machines are batch processes, so throughput is low and the products are likely to be expensive.  However, if you are adamant that thermal pasteurisation damages the nutritional and functional properties of the milk, HPP milk may be the way to go.