Spoilage
Also known as Moldy sausages, Rotten sausages, Slimy sausage, Sticky sausage
The microbial and chemical deterioration that makes a cured product unpleasant or unfit, distinct from the pathogens that make it dangerous.
Spoilage is the failure state of a cure, the point where a product becomes unpleasant or inedible. It is worth separating clearly from a safety hazard: spoilage organisms make a product unappetising, while pathogens can make a person ill, and the two do not always travel together. A cure can be spoiled but not dangerous, and, more worryingly, it can be dangerous without looking spoiled at all.
The usual culprits are spoilage bacteria such as Pseudomonas and Brochothrix thermosphacta, wild lactic acid bacteria, and unwanted yeasts and moulds, which show themselves as surface slime, stickiness, gas, off odours, souring beyond what was intended, or a fuzzy grey-green mould that is nothing like the noble white bloom. Chemical spoilage runs alongside, chiefly the rancidity that comes from fat oxidation. The same hurdles that hold back pathogens also hold back spoilage: enough salt, a low enough water activity, a clean and steady microclimate, an established surface flora and sound packaging.
Because spoilage is usually the first thing the curesmith can see, smell or feel, it works as an early warning that a hurdle has slipped. It should never be read the other way around, since the absence of any obvious spoilage is not proof that a product is safe.