Originally Posted by kitchenelf
Let me also say that "homemade" anything with an oil base and fresh garlic in it is a HUGE risk for botulism growth. You need to advise the customer of this in a way that won't offend them. There's lots of stuff on the internet. It's a disaster waiting to happen!!
Kitchenelf is right. Whilst there may be a problem with the whole cooking process used by your customer, (and you don`t know what that was!) the chances are that the fault lies with an individual ingredient. IIRC, botulism may result from canning/bottling or, as it is an earth borne organism from using an ingredient which grows in soil such as garlic.
There have been many threads about how to infuse oil with garlic on this board and other food boards, and the consensus is don`t do it as, IIRC, garlic requires heat treatment to detroy any potential, earth borne pathogen.
Now, you have a problem here! Your palatte was able to detect that something was wrong and the general consensus from posters is that there is something wrong with the batch of goodies your customer gave you. "Fizzing" is wrong, even if it doesn`t make someone ill. BUT could you live with yourself if you did not tell your customer about your concerns about their product and someone became ill and had to be hospitalised?
No, I thought not. You need to contact your customer and tell them about the problem and potential problem with their product. At the very least, the "fizzing" will continue to the point where the jars erupt and redecorate their pantry and at worst someone will become ill. Phone them up, invite them for a coffee and tell them the truth, asap.
In the meantime, if you have an opportunity, you might like to check out web sites for your country which give information and advice about home food preservation and recipes. Pull off some information which you can pass on to your customer - an attempt to soften the blow but also to help them! I am loathe to recommend any as here in the UK bottling and canning are seen in the UK as two discrete and very different methods of preservation.
Hope this helps,