Stuck sparge question

I brewed my first 20 gallon batch on a brand new system yesterday and experienced a stuck sparge (fly sparge). There was no non barley grain used. I milled the grain on the same mill at the LHBS I always use. I'm pretty sure I opened the valve too much and created a suction that compacted the grain bed, I was pressed for time and did the entire sparge in 45 minutes. I had to resort to stirring the grain bed and even put a pizza pan on top of it and pressed out as much as I could. There was still a significant amount of wort left in the tun when I dumped it. 

My question is this: If I shoot for a 45-60 minute sparge on my 5 gallon system, do I need to multiply that time by 4 for the 20 gallon system? I'm using a 26 gallon stainless tun with a false bottom. I had 52.5 lbs of grain and about 12 gallons of water and 10 gallons of sparge water,  all at about 165*F. 

captjpr3 said:

My question is this: If I shoot for a 45-60 minute sparge on my 5 gallon system, do I need to multiply that time by 4 for the 20 gallon system? I'm using a 26 gallon stainless tun with a false bottom. I had 52.5 lbs of grain and about 12 gallons of water and 10 gallons of sparge water,  all at about 165*F.

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It depends on the geometry of your mashtun and how it's designed to lauter.

A mash should have some air in it. You shouldn't beat it up like it owes you money. Stirring should be even and gentle. Fro fly sparging, I recommend you start the sparge water before the top of the grain bed is exposed. This tends to help the mash "float" a little better.

In general, the taller the mashtun, the slower you should sparge. It takes longer to get all the sugar out of the center of the mash than the sides.  With these, a sparge of 60 to 90 minutes is typical.

In some cases, the ratio of height to width is so off that equal or better efficiency is gained by batch sparging.

Thanks for the insights.

The tun is a More Beer! 26 gallon pot, approximately 1:1 Height to width ratio.

Because of the crappy lighting I couldn't really see how much water I had on top of the grain bed at the time of sparging. When it was all said and done, it appeared that I had had about 4 inches of water on top during the sparge. On the next batch I plan to have better lights and make sure I keep the water about an inch above the grain. Do you think the excessive water on top of the grain bed could have caused the bed to compact?

Another issue I had was that the tun is not insulated. I had to light the burner several times and re heat the mash while stirring to maintain my target mash temp of 155. In actuality, the temp varied from 148 to 160 several times during the mash.

It might not be a bad idea to use some rice hulls while you work the kinks out.

captjpr3 said:

The tun is a More Beer! 26 gallon pot, approximately 1:1 Height to width ratio.

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That's ok for fly sparging.

Because of the crappy lighting I couldn't really see how much water I had on top

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Was it moonlight or something? Y'now that "Man Cave" is just a figure of speech, right? ;D

Do you think the excessive water on top of the grain bed could have caused the bed to compact?

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No. If anything, it was flow rate out exceeding flow rate in and not enough air in the mash.

Another issue I had was that the tun is not insulated. I had to light the burner several times and re heat the mash while stirring to maintain my target mash temp of 155. In actuality, the temp varied from 148 to 160 several times during the mash.

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I assume you stirred? That seems like a clue that I might be right about stirring too much.

In my setup, I have a mash mixer that I typically leave running for the entire mash cycle. It very gently moves the grain around and increases mash efficiency, but it also pushes out the air and CO2 of the mash (air coming from the water pushing it out of dry grain and CO2 as a byproduct of enzyme activity).

In an effort to increase yield, I tightened my mill and added grain to recipes. I then began to notice much slower runoff, usually starting about 30 minutes into the sparge. I began shutting off the mixer about 15 minutes into the mash and the slow sparge problem went away. To further speed things up and insure against sparge issues, I'm adding about 2.5% rice hulls to every batch. Those two things took a 1500 pound grist from 140 minutes of sparge to just 70.