Question: Yesterday I made bread based on a recipe I found on the flour bag. It contained both rye and wheat flour but also three tablespoons of vinegar. I've never seen it used in bread before, why is it there?

Answer: 
When I asked this question - [Is there anything I can add to homemade bread to preserve it?](https://cooking.stackexchange.com/questions/7804/is-there-anything-i-can-add-to-homemade-bread-to-preserve-it) - Arafangion said that one commercial bread company now uses vinegar as a preservative. This is his answer to my question: 

> 
> "One commercial bread company has
>  switched preservatives... They use
>  vinegar (I suspect ordinary white
>  vinegar).
> 
> 
> Maybe you could give a little bit of
>  vinegar a go and see how that works?
>  You can still smell it if you sniff
>  and sandwiches do have a faint vinegar
>  flavour, but it seems to work well
>  enough for the company and it
>  apparently hasn't sabotaged the
>  product line...
> 
> 
> Then again, it /is/ commercial
>  bread..."
> 
> 
>
It might also, in addition to something like bicarbonate soda act as a raising agent for some types of bread - the reaction of the vinegar with the bicarb causing gas release causing rising.

This is only a guess however