I did this exact same thing yesterday. My mash tun is a 5 gallon cooler and while the math says it is good for 12lbs of grain I don't normally like to put that many lbs in there. I had a recipe that was for 14lbs of grain. I mashed 10lbs in the MLT and 4 in the pot on the stove. After draining off the first runnings of the MLT I dumped the mash from the pot into the MLT. There was more water in the pot than I prolly needed but that was my intention. I then mixed everything well and let it sit for 10 minutes. Drained again. I do batch sparging and batch sparged twice. I know this may seem like it is over sparging but I didn't get as much sparge water in the MLT as I normally would. When it was all said and done I hit 84% efficiency and had a nice looking wort. Of course it has yet to bubble from the airlock 24 hours later but I am not too worried about that. I wouldn't recommend doing this all the time but it worked this once. Frankly next time I will just add some DME to get me where I need to be.
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