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Same principle, reducing water activity (aw), is how Nutella keeps fresh for so long without refrigeration: its water activity is even lower than honey. Most ba
by Jun8 1y ago
Same principle, reducing water activity (aw), is how Nutella keeps fresh for so long without refrigeration: its water activity is even lower than honey. Most bacteria need an aw of around 0.85 to thrive, Nutella’s aw is around 0.4, honey’s around 0.5-0.6. Peanut butter is 0.7, so it stays fresh for relatively long, too.
Here’s the definition of water activity from FDA:https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/inspection-technical-guides/water-activity-aw-foods https://www.fda.gov/inspections-compliance-enforcement-and-c...
- bob1029 1y agoManaging moisture levels is probably the #1 way to control microbial activity. You see the exact same idea in HVAC - if you can keep the relative humidity below 50%, mold growth becomes nearly impossible. In laundry care, the dryer does all of the sanitizing action. Etc.
- computerphage 1y agoWhy is it relative humidity that matters here instead of absolute humidity?
- bob1029 1y agoRelative humidity is an easier unit to work with because it auto scales with temperature.
- OJFord 1y agoI think GP knows that and it's exactly their point: why do you need slightly less water to stop mould growth as the temperature slightly drops? (If anything, one might expect the opposite anecdotally - it's e.g. hot and humid bathrooms that are particularly prone.)
- stinos 1y agoIn the end drying grass to create hay is also the same principle: dry enough (say < 15% water) and it doesn't do much at all, being pretty dead. Higher and you get all kinds of life having its go at it.
- bratwurst3000 1y agoi grow weed( legal here) and its the same. last two weeks moisture and temp down because of fungi. and when harvesting the goal is getting the humidity of the buds down to 12% fast. the difference is so obviuos. sometimes in the summer heat and humidity are out of controll and thats when buds rotten :/
- cjrp 1y ago> Higher and you get all kinds of life having its go at it. Yep, and you end up with silage if it's stored anaerobically.
- grues-dinner 1y agoThis is something that I think about sometimes. Life on Earth has had billions of years and expanded to fill so many niches, but they're nearly all damp niches. Nothing has ever really managed to really thrive in deserts. Sure, there are a few cacti, succulents, a bit of scrub, a few palms and rodents and a few birds that eke out an existence. But really it's mostly barren, compared to temperate or tropical climates where nature takes over land entirely within years. Yes, the soil in deserts is poor, but that's a consequence: it was poor everywhere before plants conditioned it. It's just that evolution has never in a billion years hit on a way to capitalise on all that sunlight and those day/night temperature gradients without enough water to float all the microbiology in. Probably just as well (invoke some kind of anthropic principle here if you like) or we'd have, say, fungus there can quickly eat dry things and storing food or building anything with longevity would be much harder.
- ViscountPenguin 1y agoCacti aswell, mostly thrive because of desert floods. They've evolved to quickly suck up as much water as they can, then they use a special acidic form of photosynthesis to make it last as long as possible. Different desert plants use similar ideas, the Aussie outback for example blooms for about a month after a given flood, reproduces, then dies out near completely except around the occasional waterhole.
- highfrequency 1y agoMore counterintuitively: why hasn't any major bacteria evolved to feast on lipids like oils? Much denser source of energy than desert dirt.