Soups or stews souring?

[radtek]

I recently started reading and trying recipes from J. Child's collaboration "Mastering the Art of French Cooking, vol. 1".

 

She mentions not to cool soups or stews while covered as this will lead them to "sour". I have not observed this phenomenon.

 

But it raises serious concerns and questions in my own mind as it conflicts with my established practice. I've followed JC's instructions as closely as possible and have been exhilarated with the results. So I'm inclined to trust her and have adopted this practice for the time being.

 

Any ideas about what she's talking about?

[Shalmanese]

Julia Child lived in a time when cooking knowledge was largely passed down through folklore and tradition and she's probably just repeating lore that was commonly accepted in French kitchens at the time. I wouldn't put too much credence by it. Along with commonly repeated but wrong beliefs like searing seals in the juices and you should never wash mushrooms, there were also some truly wacky beliefs like menstruating women couldn't whip egg whites. I think this falls into the same category.

[paulraphael]

True enough, but it's still considered unsafe practice to cool soup or stock covered. You lose the mechanism of evaporative heat loss, so the soup will spend much, much too much time at temperatures that promote rapid bacterial growth.

 

It's important to cool the soup uncovered, and if it's a large enough volume that it will take more than a few hours to get it from 130F down to 40F, you need to play an active role in the process.

 

This may mean transfering to a few smaller, shallower containers, stirring in a water bath, or an ice water bath, or with an ice paddle. At home I'm rarely dealing with more than 8 quarts or so, so I try to get it down to 50F within a couple of hours, and then I'm pretty comfortable putting in the fridge.

 

Winter is easiest. If it's really wintery out, I'll put the whole pot out in the snow and wind. This is one of the few times a covered pot is ok. Old man winter packs way more convective cooling power than a fridge.

[Martin Fisher]

I agree that cooling covered stocks and soups is bad practice.

Souring is possible, at least theoretically, since there are spore forming lactic acid producing bacteria that could survive the heat and then thrive when conditions are right.

 

More possible risks associated with slowly cooling or holding stocks and soups at low temperatures.......

 

Bending the Rules on Bacteria By HAROLD McGEE

Edited March 19, 2014 by DiggingDogFarm (log)

[radtek]

Hmm. I often do not have large volumes to cool. When I do have an excess of two quarts- a water bath in the sink (covered) happens. Helps speed things up especially in the warmer months. I've always been concerned with air-born bacteria falling into a cooled environment while still in the danger-zone, so have religiously kept saucepans covered.

 

It'll be a process change for me then. No more covering a pan and wandering off while it cools.

 

I'm assuming the threshold would be 165F on this. Lower than that one should warm and serve or chill uncovered and refrigerate. 

[paulraphael]

What do you mean by the threshold being 165F?

[radtek]

What do you mean by the threshold being 165F?

This is where the dangerzone for potential bacterial growth appears and the serving zone ends. I'd assume one could cover the pan/pot to keep contents hot yet set it aside for serving as the rest of prep comes together. If it cools too much (into 165 range) it would need reheating. But, one could start the actual cooling process uncovered then for unused portions.

 

I'm not much in favor of Ruhlman's practice stated in the article. Yes perhaps in days of no refrigeration, but we have other options now...

[gfweb]

Ruhlman is stubbornly on the wrong side of this issue. Getting away with something isn't the same as good practice.

[paulraphael]

This is where the dangerzone for potential bacterial growth appears and the serving zone ends. I'd assume one could cover the pan/pot to keep contents hot yet set it aside for serving as the rest of prep comes together. If it cools too much (into 165 range) it would need reheating. But, one could start the actual cooling process uncovered then for unused portions.

 

I'm not much in favor of Ruhlman's practice stated in the article. Yes perhaps in days of no refrigeration, but we have other options now...

 

Officially, the danger zone is from 40F to 140F. These are the guidelines used by the FDA and most local health departments.

 

Realistically, there aren't any foodborn pathogens that reproduce above 131F, and all the common ones stop about 5 degrees cooler than that. You can actually pasteurize food at 131F ... which means more time at this temperature actually makes it safer.

 

I believe 165F is a temperature at which most active pathogens are killed within a few seconds. I would be careful with this number, though, because the exceptions are important. In certain kinds of food, like sweet and high-fat dairy products (ice cream bases) it takes a few minutes at this temperature. And bacterial spores will not even flinch. To kill some of the more common spores you need a rolling boil for 15 minutes or so.

 

Spores are one reason cooling on the stove can be trouble. When conditions are tough for certain bacteria, like botulinum, they make spores. These can survive most environments, and then incubate when conditions are better (anaerobic storage, or the gut of someone who's immune-compromised).