Wet bulb temperature and the stall.


 

Dustin Dorsey

TVWBB Hall of Fame
Something that Donna Fong said in either the Q&A on in response to a question in this got me thinking about this. She mentioned wet bulb temperature. For instance in Texas BBQ (or really in any commercial setting) they are cooking a lot of meat on the pit, and therefore the wet bulb temperature will increase because of all the humidity produced from all that meat. Here is a pretty decent article explaining what this means and how it applies to the stall.

http://www.scienceofcooking.com/why_is_humidity_important_in_cooking.htm

The gist of it is that humid air conducts heat better. That stall occurs due in part to evaporative cooling but also because wet meat cooks at the wet bulb temperature and one the surface dries(also forming that delicious crust some of us crave), the meat is more effected by the dry bulb temperature. On a dry North Texas day I've been experiencing some absolutely wicked stalls lasting sometimes 6 hours. Wrapping overcomes this so well because in the enclosed environment you have essentially 100% humidity and the wet bulb temp = dry bulb temp. What Donna mentioned is the reason many Texas BBQ place don't have to wrap is they are cooking enough meat that the wet bulb temp is higher than if a regular joe like myself is cooking one brisket on my WSM.

I guess my question is, especially in a dry environment, should we revisit the water pan? I, like most folks on this forum, and even Harry Soo and Donna Fong just wrap the pan in foil. There idea is that they are going to wrap once they've got the crust they want (which makes total sense.) My temperature control doesn't suffer at all. Some, such as Enrico, use a separate pan and only apply moisture during a portion of the cook and wrap with butcher paper. These are just some thoughts I've had. I like the idea of not wrapping but when I don't wrap at all, in all honestly sometimes the crust is TOO much. I can barely cut through it to slice the brisket.
 
Hey Dustin. Thanks for the link. You have some interesting questions about this topic. I live in the dry desert of AZ, so i can relate. For me, the water pan was just too much hassle. After the second time spilling water into the coals, not including the cleanup hassles, I stopped using water for good. I have taken to the occasional spritzing with water or apple juice, then wrapping--depending on the meat. Funny thing is that I never seem to need to wrap pork butts, but I always wrap ribs and briskett.
 
Dustin, thanks for posting that link. I've seen it before but lost track of it. What's very interesting (and nerdy to the max) is the link to the egullet forum of chefs and food scientists.

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

There's a good discussion of the conversion of collagen and fat rendering, and while they may contribute to a stall-like condition, they aren't at all part of what we see as a stall. Scroll down to where the poster "nathanm" describes the result of slicing a raw brisket in half, putting one half in a sous vide bag and then cooking the two in the same oven. The proof is pretty definitive that the wet-bulb theory is the right one.

Net-net is that if you cook with no water in the pan, you should probably cook at a higher temperature and wrap at the stall. If you cook with water, you can go either way.

Your observation appears correct, that when a barbecue restaurant loads a smoker up with a lot of meat, it cooks at wet-bulb temp because of all the humidity being released by all those pounds of meat. Now I know why Aaron Franklin recommends a water pan in a stick burner when you're cooking one brisket, but you don't see a water pan in one of his custom cookers when it's got 40 briskets cooking.

This is an interesting topic that I don't completely understand as it pertains to barbecue, but makes a great deal of sense from the thermodynamics standpoint.

Jeff
 
I started out in mechanical engineering. I washed out of that before I got to the thermodynamics and heat transfer classes. I switched majors to a 4 year electronics engineering technology program before I graduated from Texas A&M. The thermodynamics stuff is definitely over my head. I dunno if I'll go back to using the water pan. It definitely causes a lot more fuel consumption but if you are getting better cooking, then maybe its worth it. My problem is I have nowhere to dump the water. I made that mistake once and my dogs went nuts rolling around in it. You can let it boil out but cleaning the pan is a mess.
 
Why not use a "wick" type of humidification? Not owning a WSM and having the humidity we have here in Michigan, my brother,doesn't seem to have much trouble but who knows?
 
As far as fuel consumption goes, i ran two cookers last summer side by side on a pork butt cook, and the one with a Piedmont Pan full of water used less fuel, and less water than the stock 2009+ style pan did.
 
I started out in mechanical engineering. I washed out of that before I got to the thermodynamics and heat transfer classes. I switched majors to a 4 year electronics engineering technology program before I graduated from Texas A&M. The thermodynamics stuff is definitely over my head. I dunno if I'll go back to using the water pan. It definitely causes a lot more fuel consumption but if you are getting better cooking, then maybe its worth it. My problem is I have nowhere to dump the water. I made that mistake once and my dogs went nuts rolling around in it. You can let it boil out but cleaning the pan is a mess.

Haha, I started in ME as well. I ended up with an English degree (long story) but have found the engineering foundation to be most useful throughout the years. The no water/wrap approach works well for some people. Not me. I have tried it a number of times and have always messed it up one way or the other. Water makes for a no-surprises cook for me. I have a newer 2-gallon water pan and I usually just fill it with hot water at the outset and let it go. I evaporates down to a quart or so and the end of most cooks. I have a fairly large fire pit out back and burn tree trimmings and such fairly often. I just dump the small remaining bit of water and all the ash in the pit and forget about it. I even stopped wrapping the pan in foil. I just hose out the major grease and move on.

I did a pork butt a few weeks ago and it hung in the stall at 151 for about 4 hours. I came very close to wrapping, but resisted the temptation. Turned out fine in the end.
 
My theory on "the stall": Latent heat. Latent heat is the absorption of heat that changes the state of a substance but not the temperature. The substance, collagen. Similar to boiling water, it doesn't take a pan of water long to reach 212 deg., but it takes a long time to change it all to steam, still at 212 deg. The change of state of collagen is apparently 165 - 170 deg. afterwich the meat can increase in temperature.
 
The collagen phase change theory has been pretty thoroughly debunked as the cause of the stall. Dustin's first post in this thread covers it pretty well. A lot of it is evaporative cooling. I know that sounds implausible but it's fundamentally the same phase change principle, just of liquid water within the meat turning to vapor when it works its way to the surface. The web bulb/dry bulb stuff is a bit over my head aside from the basic principle that water is a better conductor of heat than is air.
 
The best wet bulb/dry bulb temperature analogy I've heard is to consider how hot you feel in 90° heat at 90% humidity versus how hot you feel in 90° heat at 20% humidity. The evaporative cooling effect is significant.

Jeff
 
The collagen phase change theory has been pretty thoroughly debunked as the cause of the stall. Dustin's first post in this thread covers it pretty well. A lot of it is evaporative cooling. I know that sounds implausible but it's fundamentally the same phase change principle, just of liquid water within the meat turning to vapor when it works its way to the surface. The web bulb/dry bulb stuff is a bit over my head aside from the basic principle that water is a better conductor of heat than is air.

In all honestly it's over my head as well, and I'm not sure how to apply that information. I thought using a water pan might make some difference, but it practice it doesn't seem to.
 
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