The thin line between rot and fermentation

 There's a somewhat hair-raising article on CNA with the title:

Adventures in DIY fermentation: From onion-chilli paste to grasshopper garum

 and it ends on this note which keeps me away from home experiments: 

This fermenting business needs an intrepid spirit and a sense of humour. As the Noma team put it: “There is a thin line between rot and fermentation.”

Consider this recipe for example:

“In the typical southern Tunisian home,” she wrote, “the cook will slice around seventy pounds of fresh onions, toss them with salt and turmeric, pack them in earthen jugs, and leave them for three months to become soft and wet.”

Wolfert’s version of hrous was simplified and shortened for convenience. But the long Tunisian path proved irresistible to me. When I finally popped open the lid on the onion jar, stashed in a cupboard, the ripe pong was admittedly something best kept away from anyone you might be hoping to feed. But the finished paste was sensational.

But the most horrifying idea is this:

There is nothing more highly prized at Noma than the grasshopper garum. This long, sophisticated, chocolatey potion is so versatile and so good they had to stop it popping up in too many of their dishes.

Noma suggests using live grasshoppers as well as wax worm larvae, little cream-coloured wrigglers that definitely look better as moths. Sourcing initially looked simple but, in the required quantities, it turned out to be a Google-defying mission (one example from my search history: “Are pet shop grasshoppers safe for human consumption?”).

I didn’t relish seeing the little critters jumping around in my food processor either. My squeamish compromise was cricket flour, a high-protein powder, which I am told makes a mean chocolate brownie and is catching on fast among insect eaters. 

I won’t go into the details of my encounter with 300 grams of wax worms, but let me just say that, when working in bulk, the sawdust is hard to separate from the larvae.

 So, the basic point is - if fermented foods are going to smell bad anyway, how does one tell if it's a "don't eat this, it'll make you sick" sort of bad smell, instead of "it's fine, it's meant to smell like that" kind of bad odour.

 Reader Tim, who seems unduly interested in fermentation, but I assume has not gone so far as putting live grasshoppers in his blender,  may care to explain...