Mash parameters effecting attenuation

[Bilsch]

After switching to the LoDO method a few months ago I have noticed a reduction in attenuation compared to my previous brewing experience. My redesigned mashing system is a fairly standard unit based off some of the less complicated designs from other members here. It is simply an 8.5 gal kettle with two ports, a false bottom and a chugger pump for circulation. I use manual direct fire gas heating that is very controllable in intensity. The general mash program I’ve been using is: dough in by underletting with 65c water, adjust to 62c and hold for 1 hour. Then heat @~1c/min to 71 and hold for an additional hour. I have and use 3 separate thermometers including a calibrated thermopen.

Research and consultation with a couple members have pointed to the following as possibilities:

-A combination of hot spots or heat gradients in the kettle due to too little circulation or too high heat input. If this is the problem then it will be difficult to improve without pulling too much volume though the grain bed and thus compacting it and restricting the flow. This then just aggravates the situation.

-Slow strike underlet transfer rate at too high a temperature, attempting to account for loss of heat to grain and end up with an ideal initial mash temperature of not below 62c. Thus the bottom of the grain bed is seeing higher temps during underlet transfer favoring alpha amylase. Usually my initial transfer is complete in under 8 minutes but some high diastatic grains can fully convert in 20 minutes in the alpha temperature range. I might have to rethink keeping the initial mash temp at or above 62c.

-Thin mash due to full volume mash diluting and or stressing beta amylase. Seems the jury is still out on how much of an effect thin mashes have on enzyme performance. To test this theory I would have to devise a way of doing a smaller volume mash in the beta range then continue to transfer the full water volume in during the alpha temp range. Then the issue becomes how to hold two volumes of water and protect them both from oxygen ingress.

-pH of mash. All of my LoDO mashes have been falling in between 5.38 to 5.55 and while there is contrary information as to the proper pH for beta-amylase I believe that this pH range should not be putting undue stress on beta.

-Turbulence from the pump or pressure drop due to valve restriction or recirculation through lines damaging enzymes. I’m not sure if this is a thing that could effect enzyme performance but is another new parameter that has been introduced in the change to LoDO.

-And lastly there is a possibility that the metabisulfite addition or the reduced oxygen situation in the mash it creates could be hindering beta performance. No idea here however I am certain about is that in my previous HiDO life, attenuation was never an issue, now it is and so all possibilities must be considered.

Slowly working this problem by only altering one parameter at a time is taking a while to track down the attenuation issue. I thought I’d toss this out there to see if others have had any similar experiences they would like to share.

[Owenbräu]

Have you confirmed it is not a cold fermentation issue by doing a FFT on your wort? With the cold fermentation and lagering, I'm seeing pressure build in the spunden vessel for a couple weeks, which tells me the yeast are taking their sweet time with the last few points of gravity. The FFT should tell you if it is a time issue, stalled fermentation or fermentability issue. You should still be able to pull a sample, throw it on the stir plate and test the EVG. If it has lagered clear, then you may need to pitch some some krausen from a new batch (5-10% of total volume of your FFT).

That said, centrifugal pumps are hard on yeast, but I've not seen anything on shear stress and enzymes. You might try to dial in your mash pH between 5.2-5.4 to optimize the range for beta. I may need to look into this more, but my assumption was always that the liquor:grain affected fermentability because of the higher buffering capacity raising the pH by adding more water. Thinner mashes generally require more time simply because of the physics of enzymes being less likely to come into contact with their substrate due to dilution.

[caedus]

what attenuation are you getting?

[Bilsch]

Yes.. sorry I did forget a lot of supporting information. I did perform a FFT on about half the batches with bread yeast as outlined by the Kaiser. The tests were close to what the yeast reached, +or- 1.005 or so. Final gravities ranged from a high of 1.028 on my first batch to the lowest of 1.015 after lowering the temperature of the strike water several times, which is what I had initially suspected to be the culprit. But from subsequent batch testing it turns out to not the whole story. Last batch using Best pils malt, with an initial rest of 60 min @ 61c, then 30 min @65, then 30 min @ 71 I could not break through 1.015 terminal gravity. Something definitely strange is going on.

[caedus]

I thought HochKurz was 30 min @ 61C, then 60min @ 70C?

[Weizenberg]

Hochkurz is generally a modern version of the double decoction mash introduced in the 1960's. Generally there are no fixed times, but generally used ranges.

I've only heard people in the US referring to an infusion mash as Hochkurz (still makes me twitch), but the principle are the same.

For infusions the usual range would be 20-40 minutes at 60-65C for the maltose conversion.

This requires a reasonably even heat distribution and correctly calibrated thermometers, otherwise you may need to adjust this even further.

Hope this helps

[Brew4Fun]

[Bilsch]

I believe my attenuation issue is finally resolved and all evidence points to the crush being the culprit. The first clue was not being able to get close to the 1°c a minute temperature ramp profile without over heating the lower part of the mash. Obviously circulation was an issue, especially during in the first 20 minutes or so of the mash. Too little flow through the grain bed was hampering heat exchange from the bottom where it’s heated then through the pump back into the top of the mash.

To check what was happening I removed the mash cap and gently probed with a long spoon only to find the grain bed very stiff and compressed onto the false bottom by the suction of the pump. My system is equipped with a ball valve restricting flow that is never more than about 50% open. So it seemed most probable insufficient flow through the grain bed had to be the problem vs too great a volume delivered from the pump. More than likely the situation was aggravated by the fines of the over crush further clogging the column blocking free liquid passage. The improving flow over time was perhaps attributable to the finer material gelatinizing, converting and going into solution thus opening up more flow channels through the column. Because the excess powdery starch limited the flow early on, that then reduced the contact time, surface area and thus efficiency of the maltose rest. Later the improving flow combined with the increasing temperatures of the mash profile gave alpha amylase a better shot and doing more of the conversion resulting in poorer attenuation.

Maintaining a closed system as much as possible from oxygen made finding this problem more difficult with not wanting to ever remove the mash cap and go mucking around in the grain. Poor crush seems like a pretty rookie mistake but since my mill is set to a conservative .036” gap it really didn’t stand out initially as a suspect since historically finer grist results in better attenuation. Anyway I have since increased the gap to .048” and that seemed to solve the problem with surprisingly little or no loss of efficiency in the latest batch.

I’m using the MM3 and would love to hear what others are using as their mill gaps.

[Bryan R]

I use a captain crush 3 roller, and I am as tight as the eccentric rollers allow me to go....020 or less. Another tidbit is to only restrict the output of the pump, so leave all valves all the way open, and only throttle in on the out side of the pump( say on the wort return entrance). These mag drive pumps hate their in side throttled.

Cheers!

[Taswegian]

I was getting compressed grain bed with 0.035" setting, but then changed to underletting the mash water and conditioning the grain. I now crush with 0.025" setting and don't have any issues. Those two things made a big improvement to flow through the grainbed.