Losing Efficiency with 5 gallon batches

Greetings fellow brewers..........

So its been boggling me all week, and I need an answer. Typically my friends and I brew 10 gallon batches, infact since going all grain that is all we have done. We are always right around 80% efficiency. Last week we did two "small" batches of 5 gallons. We followed the same steps, same as we always do......but we missed our OG's by alot! I am talking almost .020 points....after adding some sugar to the boil we were able to cover that spread a little but what gives???

Talking to some people at our homebrew meeting someone else said they had that issue and they were thinking it had to be something with thermal mass. The fact the mash tun was only half full versus full. Our setup is a 10 gallon converted cooler and 24lbs of grain gets us just below the top, perfect size. However, the 5 gallon batch was only half (obviously).

Anyone have any ideas, or know why??? If indeed it is this thermal mass theory, can someone explain this?? Perhaps how to counteract it???

Thanks!!

what sparging method are you using?

the smaller batch will lose more heat, so did you add any boiling water to correct that, and what SG were your final sparge runnings....

We use fly sparging.......have a pvc manifold that sprinkles the sparge water over the top........

We did not add any boiling water to correct that......the SG of the final sparge runnings were 1.020ish.......shooting for 1.056 preboil and we were at around 1.042.......had to add sugar to get it up......

Thats an interesting thought that the temp got to low....but I can't imagine that was it b/c we just tasted it transfering to secondary and it wasnt a thin beer (low mash temp).......

baffeled...

lostboysbrew said:

We use fly sparging.......have a pvc manifold that sprinkles the sparge water over the top........

We did not add any boiling water to correct that......the SG of the final sparge runnings were 1.020ish.......shooting for 1.056 preboil and we were at around 1.042.......had to add sugar to get it up......

Thats an interesting thought that the temp got to low....but I can't imagine that was it b/c we just tasted it transfering to secondary and it wasnt a thin beer (low mash temp).......

baffeled...

Click to expand...

Bed depth will effect your fly sparge. Could be you got some channeling and only rinsed a portion of the grain bed. Could also be that you have some dead space in your cooler and the ratio of dead space is higher with a smaller mash.

Is this a rectangular cooler? Those low, wide rectangles are harder to fly sparge with smaller batches. Cause the bed depth becomes an issue.

Yes it is a rectangular cooler..........didnt have any channeling as i was keeping a close eye on that.....stirring up the top of the mash without disturbing the grain bed.......

what does having deadspace in the mash tun affect???

I wouldn't fly sparge a 5 gallon batch in a large rectangular cooler, grain bed too thin. Deadspace is a pocket under the manifold where the highest gravity wort just sits and never leaves.

I'm thinking you only really rinsed the portion of the grain bed nearest to the drain. This could be something that you can't see without dye in the sparge water. This is why the tall round coolers with a false bottom are better suited to fly sparge.

Bobby_M said:

I wouldn't fly sparge a 5 gallon batch in a large rectangular cooler, grain bed too thin. Deadspace is a pocket under the manifold where the highest gravity wort just sits and never leaves.

Click to expand...

I have seen my effeciency drop pretty drastically with my last 3 batches as well. I do have a lot of dead space and this seems to make sense. How can this be corrected? Would I need a different setup or add a copper tube to siphon out the wort? I use a 10 gallon pot with a false bottom that sits pretty high and just open it up while sparging.

geer537 said:

I have seen my effeciency drop pretty drastically with my last 3 batches as well. I do have a lot of dead space and this seems to make sense. How can this be corrected? Would I need a different setup or add a copper tube to siphon out the wort? I use a 10 gallon pot with a false bottom that sits pretty high and just open it up while sparging.

Click to expand...

You open what up when sparging? If your fly sparging you need to go slow to get the most rinsing action.

If it has a spigot, you can run a tube from the spigot down to the bottom of the pot, it will make a siphon and pull of most all of the liquid.

I am fly sparging and I'll fashion one of my spare tubes to hook up to the spigot. Thanks!

I'll back out of the conversation now so as not to high jack someone else's question.

maida7 said:

I'm thinking you only really rinsed the portion of the grain bed nearest to the drain. This could be something that you can't see without dye in the sparge water. This is why the tall round coolers with a false bottom are better suited to fly sparge.

Click to expand...

Havent had anymore problem fly sparging before.....we have a manifold that sprinkles water evenly over the entire cooler so the water was spread out over the grain bed. And like i said, 10 gallon batches we have no issues.....

Bobby_M said:

I wouldn't fly sparge a 5 gallon batch in a large rectangular cooler, grain bed too thin. Deadspace is a pocket under the manifold where the highest gravity wort just sits and never leaves.

Click to expand...

Our manifold sits on the bottom, there isn't a whole lot of dead space in there. However, is there a way to counter act this???

lostboysbrew said:

Havent had anymore problem fly sparging before.....we have a manifold that sprinkles water evenly over the entire cooler so the water was spread out over the grain bed. And like i said, 10 gallon batches we have no issues.....

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yeah, whatever, don't believe me. The grain bed is thinner with the 5 gallon batch. No matter how you sprinkle the water it's gonna have some channeling and the flow will prefer to run closer to the drain.

Go read Palmer's book How to Brew. He has some great diagrams of how a fly sparge works.

maida7 said:

yeah, whatever, don't believe me. The grain bed is thinner with the 5 gallon batch. No matter how you sprinkle the water it's gonna have some channeling and the flow will prefer to run closer to the drain.

Go read Palmer's book How to Brew. He has some great diagrams of how a fly sparge works.

Click to expand...

I wasn't doubting you, I was purely explaining that I didnt think there was any channeling.......dont think the attitude was necessary. Have read Palmers book........was just looking for some discussion as to why our SG was so off........thanks for your help