Not sure, but have you tried heating the bottles before filling them & sealing them? Then when they cool off if anything they should have a vacuum seal, like when you can things in mason jars. No clue if it would work, but it sounds good to me :)

Let us know if you get your problem solved.

J

there has to be some microbial reaction in order for the gas to be given off. you have a food safety problem. try a different testing lab.

pack the sauce hot then chill it. thats how we get the safety lids to suck down on the lids of jars.

You cannot really "vacuum seal" the 5oz bottles with plastic lids, atleast not in the traditional sense of vacuum sealing canning jars, etc. You can heat your product up and when jarred at the proper temp the lid will "seal" somewhat.
What temp are you heating your final product to before bottling up, possibly your product is not being heated high enough and then fermentation is starting back up in side the bottles. You need to be pouring it atleast 185 degrees I believe in order to kill/stop any possible buggies that could produce fermentation. This can cause leakage and possible explosive hot sauce..:)
Does your lab test the ph of your sauces? This is the test you need to deteremine whether you are safe to sell it or not. If you are getting leakage (possibly due to fermentation) then there is most certainly something growing in your product, bacteria, yeast etc.

kendra

try pressure sensitive lids. also, you may be filling your jars too full. cut back on the amount of product in your bottles and see if that works. i know with some of my salsas and sauces, the expansion rate is greater than that of my other products.