Q:

How much citric acid is safe to use? 

I am using citric acid as a preservative for peanut sauce.  The 1tsp per quart is not strong enough.  Is it safe to use a higher concentration?  My peanut sauce is currently at a pH of 4.5, I need <4.3.  I don't want to water down the sauce any more than it already is.  I will be hot pack bottling, maybe. 

A:

According to (US) Code of Federal Regulations on Citric acid:

(c)  In  accordance  with  § 184.1(b)(1),  the  ingredient  is  used  in  food  with  no  limitations  other  than  current  good  manufacturing practice. ( d) Prior sanctions for this ingredient different  from  the  uses  established  in  this  section  do  not  exist  or  have  been  waived.  

Basically, you can eat the stuff by the spoon-full if you can stand the sour. 
If you're adding a lot compared to how much you think you should have to add, you might consider Phosphoric acid instead.  You get a little more bang per mole pH-wise with that, and it too, within limits, is generally regarded as safe (GRAS). 