Off smell in beef/chicken stock (suggestions please?)

Joined Apr 28, 2019
I'm preparing a very simple stock from a traditional Northern Italian cookbook, and running into an issue:

beef brisket
beef knuckle bone
chicken: 1 thigh, 1 leg (bone in)
whole onion

The recipe calls for simmering all ingredients together for 7 hours. I'm using a very slow simmer - circulation below the surface, with few to no bubbles breaking the surface.

Tasting as I go, everything is going great for the first several hours - flavor is developing, and tastes great. Then within the last hour or so, a funky sour smell develops that is very prominent when I take a whiff. I've done this three times, checking my ingredients very carefully for freshness each time, and each time the same result. I've done both with skimming and without (the recipe calls for not skimming, but I'm so used to it).

It's also a flavor, but more subtle as a flavor than as an odor.

Of all my ingredients, the funky smell/flavor is closest to the celery, but only vaguely. If you smelled/tasted it with no further information, I don't think you'd associate it with celery.

Can anyone advise me? One idea: I know most vegetable stocks call for only about 45 mins simmering. Is it possible for the vegetables to go too long and develop this off smell?

Any other ideas for what is going on?

Thanks in advance to anyone who can help :)
Joined Jan 9, 2019
I'd be blanching/skimming the meat (separately), rinsing, then doing the slow simmer, covered.
Otherwise you're probably just making a nice 7 hour bacteria culture.

{edit} Can also sear the meat for a nicer brown stock, but again a pre-blanch might be in order.
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Joined Mar 1, 2017
First, you don't need to simmer your stock for that long. 2 to 4 hours max is all you need to achieve max benefit from your ingredients. Otherwise, you're just making jelly, which is fine if that is what you're going after. But, the meat and veggies have given up all of their flavor after 2 to 4 hours.

Transglutaminase Transglutaminase is right, IMO. Blanche your meat for 2 to 4 minutes in boiling water first. Rinse and drain. That removes most of the meat's impurities. Fill the pot with cold water, add your meat and veggies and simmer. Don't forget your pepper corns, boquet garni and clove or two of garlic for some character.

Good luck. :)
Joined Aug 15, 2003
Where did your meat come from?

And yes, IMO, vegetables should be added in the final hour or two of making stock in order to preserve the aroma.

One possibility is that your heat is not evenly distributed and the top part of the stock is cool enough to breed bacteria. This is unlikely but if your temp is too low it could happen. Maybe turn your heat up a bit or make sure you stir the stock (gently) every hour or so.
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