Why must fermenting meat be kept cold, but not vegetables?

Question

This is a somewhat unique question, so I'll start by stating my assumptions that I understand to be "widely known" among food preservation enthusiasts. If any of these are not accurate, please let me know!

Assumptions:

1. Improperly handled food kept at low oxygen (e.g. submerged in liquid) carries a risk of causing deadly botulism.
2. The bacteria that create botulism toxin require certain conditions: low oxygen, low acidity, low salt, low sugar, sufficient protein content, correct temperature range.
3. Lacto-fermenting vegetables in a salt brine carries little to no risk of botulism, and no case of botulism has ever been reported from lacto-fermenting vegetables.
4. Lacto-fermenting meats and dairy products must be done in a cold environment like a refrigerator to prevent the risk of botulism.
5. Lacto-fermenting protein-rich vegetables (e.g peas, beans) can be safely done at room temperature.

So my question is: what's so special about meat and dairy that it carries a high risk of botulism? Botulism can occur from improperly canned beans, yet fermenting beans at room temperature is okay. Why is it not okay to lacto-ferment meat at room temperature? What's different about meat vs. high-protein vegetables?

And a follow up question: could there be any substitute safety measures other than refrigeration to make room temperature meat fermentation safe? E.g. Extra salt, acid, finely shredding the meat (to ensure brine penetration), etc.?

Edit:

My main motive for this question is determining whether room temperature preservation of cooked meet is possible using a salt brine + other vegetables / ingredients in a process similar to lacto-fermentation; I'm not concerned with the technicality of whether the bacteria feed off the meat or if the meat truly "ferments"; I'm only concerned with preservation. Example: if adding freshly cooked (i.e. mostly sterile) meat to a jar of fermenting vegetables (at any stage of fermentation) effectively prevents spoilage of the meat, I would consider that an answer to my question. If not, the reason why not would also be a good answer.

Answer 1

It is a good thing that you wrote up your assumptions, this helps greatly with explanations. To look at each:

• Assumptions 1,2 and 3 are true.
• Assumption 4 is false. You can't lacto ferment meat. There is only the edge case of cured sausages, and their fermentation process is very far from the lactofermentation of vegetables. Lacto fermenting dairy is done at high temperatures - from about 20ish celsius for Kefir, to up to 45 for some strains of yogurt culture.
• I can't comment on Assumption 5, since I have never looked into lacto-fermentation of legumes.

Looking at these assumptions, it looks as if you are equating the absence of botulism bacteria with food safety. This is certainly not the case! There are dozens of different kinds of bacteria which can cause food poisoning, most of which are more difficult to guard against than botulism bacteria.

Whenever you leave some food sitting out, you create a new microenvironment which gets colonized by its own ecosystem of microorganisms. Which type of organism will grow and displace all others is dependent on the conditions you offer it, just like in your assumption 2. It just so happens that, if you leave out vegetables at room temperature with the right amount of salt, it is the benign lactobacilii which proliferate best and occupy all the ecological niches in your fermentation jar. By the way, your fermentation can go wrong and create the wrong microorganisms, but they will not be c.b., that is usually seen under much stricter anaerobic conditions, such as in canned food and sometimes under oil.

But meat is not a vegetable; it is a different source of food, on which lactobacilii cannot thrive. Instead, you get other types of bacteria on meat, usually ones which cause food poisoning. To prevent that, you have to preserve meat by making it inedible for any kind of bacteria, before they have overtaken it. This creates different curing methods for it, which require very tight control and multiple bacteria-controlling methods at once (e.g. cold temperature plus the right amount of salt) to get a safe cured meat.

If you were to just leave your meat out in the conditions for a vegetable lacto-fermentation, you would get neither a lacto-fermentation, nor botulism, but just a crock full of spoiled meat, ready to give you some kind of non-botulinic food poisoning.

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Update To the point in your edit: It is absolutely not safe to just add meat to properly fermenting vegetables. Actually food safety is much more cautious than that, and any kind of self-experimented recipe is not safe by definition, but this is one of the rare cases which are not just unsafe, but decidedly dangerous. Probably not because of botulism, but the other types of food poisoning are no joke either.

Answer 2

Edit for your edit:

Fermenting the meats for long-term preservation in a moist, ambient temperature lactic acid bacteria (LAB) environment as you described would theoretically be safe in terms of pathogen growth as long as:

1. the pH both before and after adding the meats is maintained at safe levels,
2. the lactic acid properly penetrates the pieces for acidification, and
3. an isolated culture of LAB with known performance, not wild strains on vegetables, is used.

The difficulty in predicting and measuring the first two makes this highly difficult in a commercial environment before even considering a home environment. Without a thermal lethality / cook step to stop fermentation, you'd also have uncontrolled bacterial digestion leading to issues with texture and off-tastes. This is why typical meat fermentation for shelf stability today is almost exclusively done for dry-cured sausages.

What you may want to try for room temperature storage would be pickling the meats with a controlled amount of vinegar or other acid, like for pickled eggs. You could add lacto-fermented vegetables, after pasteurising them to stop fermentation, for the milder acidity and flavour - though you would need a method to measure the pH for safety.

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Lacto-fermentation was a major means of preserving meats prior to the widespread use of refrigeration, and almost every cultural cuisine has a fermented meat or seafood product. Our modern understanding of food safety and food-borne pathogens incorporates refrigeration to further reduce the risk from fermented meats and seafood.

The concern for temperature control in these kinds of fermentations are due to Staphylococcus aureus bacteria, found naturally on the skin of 1/5 to 1/4 of the human population, contaminating and multiplying enough in the foods to produce heat-stable toxins before before the lactic acid bacteria acidifies the food to a pH of 5.3 where S. aureus is inhibited. Both the US and Canada have meat fermentation temperature guidelines, aimed toward commercial operations, limiting the total time meat can be at temperatures above 15C prior to achieving a pH of 5.3 (Canada) / 4.6 (US) or lower.

Clostridium botulinum is typically inhibited with the use of added nitrate/nitrite in curing salt.

Following on from @rumtscho's statement that meats can't be lacto-fermented - meats generally do not contain enough glucose for lactic acid bacteria (LAB) to produce lactic acid, and recipes usually require added sugar for this to occur. They do produce various enzymes that break down lipids and proteins into products that give added flavours to the food as fermentation by-products. These products are still considered 'fermented meats' by most American and European food safety authorities.

Some resources for further technical information:

• Handbook of Fermented Meat and Poultry on Google Scholar
• Application of lactic acid bacteria for the biopreservation of meat products: A systematic review - https://doi.org/10.1016/j.meatsci.2021.108661
• Canadian Food Inspection Agency: Preventive control recommendations for manufacturing fermented and dried meat products
• US FDA: FDA Food Code 2017 - page 692 for smoked and cured meats, including fermented meats

Edit: there's a Korean patent for kimchi-ripened/fermented raw meat: https://patents.google.com/patent/KR20080042640A/en

Regional variations of kimchi might include raw fresh oysters or squid, in some areas meats, though this isn't common commercially - dried seafood or seafood sauces are more common. The patent describes fermenting pork belly, beef sirloin, or chuck rolls as part of the kimchi lacto-fermentation process.