Well, you said that you apply heat on the product and the jars are sterilized, so this means that the possibility of mould contamination from the jars and the product is minimized.
As Ryan pointed out, there is a high possibility that the mould is cause by the air quality of the area where the product is produced and/or packed. This means that there are particles of mould in the air, thus it is transferred into your product. You can conduct an
If the air turns out clear, you can then try higher cooking temperature.Go to the full post