Okay, no one answered and I'm sure you're done with your brisket by now. How did it turn out?
I'm not a mini owner but do have a
WSM and I smoke on my
Weber Kettles so take what I say with a grain of salt.
About the only time I see an internal meat temp drop like you mentioned is when I haven't positioned the meat probe correctly. Happened to me this morning. I just took a small 6.5 lb brisket flat off the smoker after a relatively hot and fast cook (275F-295F chamber temp for 6 hours). Initially this morning the internal temp went from 48F to 130F in an hour with a chamber temp running 275F. My instincts said "no way", it was climbing too fast. I had initially put the probe in the meat sideways from the thickest end of the cut. When I pulled it out and put it back in at an angle from the top of the brisket, careful to hit the middle of the meat, the internal temp dropped to 90F. That reading was correct. Obviously the end of the first probe ended up too close to the outside of the meat.
I'm guessing the chamber temp dropped when clouds blocked the sun. I get that kind of drop on my
Weber Kettles when the clouds or backyard trees block the sun. Run it a little hotter than 220, say 235-250 and you won't have to worry about the shade or ten degrees.
You don't say how big your brisket was. For a small 4-6 lb brisket flat 158F in two hours seems a little fast for 220F chamber temp, but it could happen. I usually see that temp in two hours on 3 lb cuts of meat. But to have an internal temp of only 138F after 5 hours, assuming the 220 remained constant, that seems a little low unless you have a 10+ lb brisket in there, then that's probably closer to accurate for 220F. Still doesn't explain the drop though.
Anyway, fill us in on the final product and what you did. We can always learn something.
