Re: What purpose does phosphoric acid serve in cola beverages?

Phosphoric acid is used to lower the pH of the cola to approximately 3.0. 
The 'magic number' for FDA regulation in the food and beverage industries 
is a pH of 4.6 (4.7 for tomato products because of compositional changes 
from plant breeding).  Foods with pH less than 4.6 are categorized as 
high-acid foods and do not run the risk of contamination by harmful 
bacteria like Clostridium botulinum (although they can be susceptible to 
yeast and mold growth).  Low-acid products (above pH 4.6) require a 
commercial sterilization process to destroy bacteria and bacterial spores 
in order to be considered safe.  Ultimately, the final composition of the 
food or beverage greatly impacts the microbiological safety of the product.

Some beverages do use other acids approved for consumption to lower the pH 
(like citric or lactic), but phosphoric is one of the strongest acids 
approved for consumption and is typically less expensive to use because of 
the smaller quantity required to achieve the same pH.

I hope this info helps!  Please let me know if I can explain this 
classification difference further.  Balancing ingredient cost and equipment 
investment is a complicated problem that food and beverage manufacturers 
struggle with when developing new products.

Kieran