If you are right, and the smell is coming from an amine, then you may need to clean a lot more than you have. Even if you think you've done a thorough cleaning, amines have very low odour thresholds. I can't find specific numbers for putrescine and cadaverine; however, another amine generated in decaying animal protein, trimethylamine, has an odour threshold of 0.00021 ppm.
We can do a back of the envelope calculation here. Volatile organic amines need to be at a concentration of 1 ppm in order for the vapor pressure to be high enough to generate an odour. Your odour is "strong" so let's choose a concentration of 10 ppm. The goal is to use our cleaning product to get the concentration of amines from their current level (10 ppm) to the desired level (0.00021 ppm) so that we don't smell it any longer. I read on many bottles of commercial cleaning products "kills 99.99% of the germs!" so let's go with that number as the cleaning efficiency. If I get rid of 99.99% of the amine in one wash, that's:
That means we need two good cleanings to get the amines to a level where they cannot be detected by our noses. Note that this is a simplified problem and assumes that the fats don't interfere with the cleaning efficiency and that you are able to clean every surface exposed to the grease with 99.99% efficiency. These are typically the limiting factors in cleaning.
These types of odours are a serious issue for swine and poultry farmers and one of their approaches to eliminating odours is through proper air flow. Get some fans going to dilute the smell, as this will make life a bit more manageable and will also help in ultimately eliminating the odour.