Off-Flavor development on Butter Toffee Almonds

I'm looking for some insight into an issue i'm dealing with at a Ready-to-Eat snack food company.

My company manufactures various candied nuts and one item seems to struggle to maintain it's quality over time. We heat ingredients in a copper panner, dump and cool the mixture on a table, bulk pack and re-pack into retail size containers shortly after. We have put the product through our stability program various times and have had "good" product into the 8-10 month range, but at times the product develops off-flavors and almost a rancid taste after only 3-4 months of being packaged. This item is offered through our "free from" program so the addition of any preservatives isn't an option. We've looked at seasonal changes in climate and almonds coming in and have had no luck, we've played with the ratios on the ingredients and have had no luck. Each batch of product follows a documented procedure and no variance in process has been noted.

I have a company that grows almonds and another one that chocolate coats them.

There have been issues with stability in how and at what temp they are stored, how and at what temperature they are transported and of course how and at what temperature they are stored at in the manufacturing facility prior to use - have you tracked back all the way to the grower as of yet and also checked to see if packaging that you are using could be causing the issue. We had a problem with a plastic container that fumed off and it imparted a plastic taste into almonds.

Does the off-flavor occur only in the combination of almonds/butter or with other fats too?

Rgds

moskito