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The dreaded BBQ stall......

DiggingDogFarm_65362

Someone is trying to convince me, and others, that the dreaded BBQ stall in NOT caused by evaporative cooling, but by "temperature and water activity equilibrium" or "water activity oscillation". Whatever that means!!!

Thoughts?

Thanks!

~Martin

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Jack_Ostrowski_46259

I found this link...not sure if it helps answer the question but they have one good data.

http://amazingribs.com/tips_and_technique/the_stall.html

seijoed

That is the most referenced paper on it I've seen, but yes it is evaporative cooling.

http://modernistcuisine.com/2012/08/barbecue-stall/

DiggingDogFarm_65362

I found this link...not sure if it helps answer the question but they have one good data.

http://amazingribs.com/tips_and_technique/the_stall.html

I'm well aware of that link and many others, but this guy is trying to tell me it's all hogwash.

~Martin

DiggingDogFarm_65362

These are some of the relevant links I have relating to evaporation cooling.

http://modernistcuisine.com/2012/08/barbecue-stall/

http://www.genuineideas.com/ArticlesIndex/stallbbq.html

http://forums.egullet.org/topic/134998-the-temperature-stall/

http://www.alkar.com/technical_reports/cooking_truth.html

http://www.huffingtonpost.com/craig-goldwyn/physicist-cracks-bbq-mystery_b_987719.html

I haven't found "temperature and water activity equilibrium" or "water activity oscillation" in relation to the stall mentioned anywhere, other than what the guy mentioned above is spewing. LOL

~Martin

seijoed

Hit him really hard til he stops?

DiggingDogFarm_65362

LOL! Good idea!

Trouble is, he's at least a couple thousand miles away.

~Martin

seijoed

Water activity equilibrium sounds like a medical condition.

Chris_Young_80640

I ran all of the experiments and wrote up the results as explained in Modernist Cuisine. I have discussed this with Meat Head and I know that he and Greg Blonder also confirmed my experimental results. So, if someone has empirical evidence that we're wrong, we'd love to see it.

Arm chair theorizing does not trump experimental evidence, so I would say show me the data that supports the alternative theory.

DiggingDogFarm_65362

I'm trying to get some specific references out of him.

So far, no luck!

That says a lot! LOL

~Martin

DiggingDogFarm_65362

Quoting him....

"The swamp cooler theory breaks down under the laws of thermodynamics as the "cooling" should indicated heat loss. Which if true would result in the consistent lowering of the meat temperature. Which is not observed.

Therefore the only way to have a temperature maintain stead is for the meat to also be accepting energy at the rate of loss.

Which is the definition of an oscillator in hysteresis.

Unless someone is interested in explains perpetual energy function of the meat in the stall then the laws of thermo dynamics say the meat has to be accepting energy and losing energy at the exact same rate. The very definition of a tuned oscillator."

swamp cooler theory=evaporative cooling

Here's a link if anyone wants to read the full exchange:

http://www.smokingmeatforums.com/t/137879/pork-shoulder-took-36-hours-to-smoke-why#post_951315

~Martin

seijoed

That was a confusing and long thread....

DiggingDogFarm_65362

Yes, it sure is!!!

~Martin

Dennis_Cloutier_38122

Quoting him....

Therefore the only way to have a temperature maintain stead is for the meat to also be accepting energy at the rate of loss.

Which is the definition of an oscillator in hysteresis.

~Martin

Actually, that is the definition of a body in thermal equilibrium with its surroundings. In other words, when the meat hits the temperature where the energy loss to evaporation equals the energy gain from its surroundings, then it sits there until the meat dries out enough that evaporation is reduced. Then the temperature starts to go up again.

Mike_Minh_Truong_54120

Both seems plausible.

Im curious how chris's experiment was set up and performed.

Does anyone know the actual amount of heat energy and time (delta t) required to change liquid water into gas? I wish I still have my thermo book with me. We can do a side by side comparison of the stall time with a piece of meat containing approximately the same liquid water content.

Also, a piece of meat is far from what engineers use to derive results. They typically use a uniform shape which is assumed to be thermodynamic throughout.

Dennis_Cloutier_38122

Both seems plausible.

Im curious how chris's experiment was set up and performed.

Does anyone know the actual amount of heat energy and time (delta t) required to change liquid water into gas? I wish I still have my thermo book with me. We can do a side by side comparison of the stall time with a piece of meat containing approximately the same liquid water content.

Also, a piece of meat is far from what engineers use to derive results. They typically use a uniform shape which is assumed to be thermodynamic throughout.

Heat of evaporation is roughly 2260 kJ/kg. Specific heat of water is about 4.2 kJ/kgC. So in other words the amount of energy required to evaporate 1 kg of water would be enough to heat 10 kg of water by about 50 degrees C. I don't know what the specific heat capacity of meat is, but I'm guessing its not too far off water. Evaporation sucks up a lot of energy.

More importantly, does this mean we should foil our pork butt when it hits the stall, or is foil evil? I've never tried it, but I'm thinking I will next time I do a butt.

Mike_Minh_Truong_54120

@Dennis

First off, pork butt is an excellent cut, especially combined with homemade fermented anchovy sauce and water spinach on the side.

Secondly, it would also require an actual cut of meat to weigh before and after the cooking process to approximate the water loss (water content).

Third, what is foiling your pork supposed to achieve? Water loss is inevitable no matter how low your temperature is.

Tim_Sutherland_52834

@Mike, foiling or The Texas Crutch is explained on Amazing Ribs.

Chris_Young_80640

@Dennis

First off, pork butt is an excellent cut, especially combined with homemade fermented anchovy sauce and water spinach on the side.

Secondly, it would also require an actual cut of meat to weigh before and after the cooking process to approximate the water loss (water content).

Third, what is foiling your pork supposed to achieve? Water loss is inevitable no matter how low your temperature is.

Mike: While it's true that water loss will occur as proteins denature, coagulate, and contract. Putting foil around the meat acts as a skin that halts evaporation. Essentially, inside the skin the relative humidity goes to 100%, which means that wet-bulb temperature = dry-bulb temperature.

Normally, you have water evaporating from the surface and the surface temperature of the food (thus, the effective cooking temperature since the inside of the food will always be less than or equal to the surface temperature) will be between the wet-bulb and dry-bulb temperature.

The funny thing about the water-activity argument is that water-activity is not actually a physical property, but rather it's a derived unit based on vapor pressure. And vapor pressure gets you right back to the idea of wet-bulb, dry-bulb, and evaporative cooling.