1st Time Fly Sparge

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Mar 23, 2017
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Well, got my 1st fly sparge under the belt last night.
Curious thing is that my pre-boil volume ended up about a quart more than predicted by BeerSmith.
I used the same 0.9600 fl.oz per oz of grain figure that worked so well for batch sparging.
Only thought I have is that somehow, the fly sparge compacted the grain bed more, squeezing out more wort, lowering the grain absorption rate.

The curve ball (has to be at least one) is that this was a large grain bill for me.
16.25 lbs of grain for a 5.5 gallon batch. I'm usually at 10-12 lbs.
Maybe the heavier grain bill squeezed itself?
My efficiencies were down, but I'm blaming the high OG (1.081) before I scrap or change the fly sparge thing.

Some system set up specs:
  • I matched the lauter rate to the pump with the ball valve on the MLT during vorlauf
  • I bought a small pump that I throttled down to 1 quart per minute
  • I measured and heated the sparge water exactly, then let the pump feed the MLT when the wort drained to about an inch over the grain bed
  • Let the MLT run dry
  • MLT has zero dead space (SS Brewtech InfuSsion 10 gallon)
  • Sparge water added to MLT with the SS Brewtech recirculation manifold resting on grain bed

Any thoughts on why my absorption rate is down?
I'm trying to figure out what your sparge process actually was. Letting the bed go dry doesn't fit a typical fly sparge. Wanna step through it again?

  1. underlet the strike water at 1.5qt/lb ratio
  2. stir
  3. mash (single infusion)
  4. stir
  5. start gravity drain into the BK (think grant)
  6. turn on pump to suck from BK back to MLT
  7. when BK if free of bits and wort is running clear, match gravity drain rate to pump rate (1qt/min)
  8. turn pump off
  9. switch pump inlet to HLT (HLT contains measured, heated sparge water. essentially what would have constituted my single batch sparge)
  10. when wort is about an inch above grain bed, turn pump on
  11. when HLT runs dry, turn pump off
  12. allow MLT to run dry (like a batch sparge)
Thanks, that's quite clear now.

It's an interesting technique - you're using a prescribed sparge volume presumably to hit a pre-boil volume, quite similar to batch sparging, while a classic fly-sparge maintains a cover of sparge liquor atop the grain bed all the way to the end of pre-boil volume collection.

The hydraulic effects of the continuous application of sparge liquor allegedly results in a definitive SG gradient slowly sinking through the bed that increases the density of the runnings that end up in the boil leaving weak runnings behind (eg: 1.006 or so). Obviously there's a lot that has to go right for this to benefit the user - a channeled bed can be a huge efficiency hit, for example, allowing sparge liquor to bypass most of the grain and go straight to boil kettle.

I'm not sure where your technique would be wrt efficiency but I'm inclined to believe it would be closer to a single batch sparge than a full-on fly sparge. That said, ending the sparge with a mlt full of grain and weak wort can be a huge pita, never mind having treated and heated all that sparge liquor that gets dumped. Adjusting the grain bill by a pound or so and taking the less onerous path would seem more rationale ;)

efficiency discussions aside, I’m in search of an explanation for the change in absorption rate.

maybe just a fluke.
efficiency discussions aside, I’m in search of an explanation for the change in absorption rate.

maybe just a fluke.

You mentioned you did a big grist.

I do no sparge, but I don't think that changes much from what you experienced.

When I'm doing big grists I change my grain absorption from 1.2 which is normal for 1.050-ish beer, to 0.78 for a 1.100 ish beer, and I vary the GA in between the 1.050 beer and 1.100 beers to reflect the amount of grain used.

Also if you sparge fast you'll get a lower preboil volume, if you sparge very slow you'll get more, given that you use a fixed amount of sparge water.
I did slow down my runoff rate for this batch. I let it run faster when I batch sparge or no sparge.

Now that actually meter my runoff rate, I will keep that consistent and see what that does to my smaller beers.
I may have to adjust my GA based on this new rate.

I'll keep an eye on what the grist size does to me as well.

Can't dial it in with a single batch.
The best part of learning to brew is all the beer!
That was the best part of learning to BBQ too!!
I'm presuming you were trying to get something like 6.5 or 7 gallons into the kettle. One quart represents 3.6% to 3.8% of the total volume. Theres a bunch of things that would account for that level of variance in a small home brew system. Are you really worried about it?
7.5 gallons pre-boil was the target, so 3.3%.

Am I really worried about it? No.
I am curious to know why this batch deviated from the predicted pre-boil volume.
I’ve never had a deviation from pre-boil volume before.
I really enjoy the predictability/repeatability.
Either, the large grain bed was to blame or it was a fluke.
Just got through a sparge with 11lbs of grain and got my usual grain absorption rate.
Interesting fly sparge method. My understanding is that most use this method of fly sparge.
1) vorlauf to get clear running wort.
2) start draining the mash tun at a rate that will take about 3/4 to 1 hour.
3) match the rate of drain with sparge water to keep an inch or two above the grain bed.
4) stop the sparge when you reach your preboil amount.
Some will stop when the sparge reaches a certain gravity or pH. I don't fly sparge so I don't know these limits.

I think that the grain absorption could also be affected by the types of grain to a certain extent. Some will trap more water than others.
with 7.5 gallon pre-boil volume:
3/4 hour = 0.7qt/min
1 hour = 0.5qt/min

I took a cue from Palmer (How to Brew) on the 1qt/min.
with 7.5 gallon pre-boil volume:
1qt/min = 1/2 hour

I got 87% mash efficiency on this last batch. I'm happy with that.
I'll probably slow it down for larger grists (like my first sparge brew, where I got 76%).