My first BIAB experience... a couple quirks?

[DVCNick]

So I was doing a Belgian Wit style recipe with 50% flaked adjuncts. Rather than pay for one time use rice hulls I figured I'd give my bag a shot.... It's just been sitting in the package ever since I got it a while ago.

The only change to my equipment setup was replacing the false bottom in my mashtun with the bag instead. Figured I'd still use the cooler mashtun for two reasons; 1) heat retention 2) even though I do have the volume or a full volume mash with this 5gal recipe, I've always had better efficiency with more sparge steps. So even for "small beer" 5 gallon batches where I have the space, I still break it into two drain steps with one batch sparge step. I also did not change my mill gap from the normal .035.

So off I went. Missed mash temp a couple degrees low at 148 instead of 150. Did a 90 minute mash and noticed maybe one degree of heat loss at the end. With the bag I figured there was no reason not to and let the drain to the kettle proceed as fast as it could with the mashtun ball valve completely open (I slow this down with the false bottom to prevent stuck sparge).

I also set the mashtun deadspace variable to zero and tilted the cooler to get virtually every last bit of residual liquid from the bottom, which I can't do with the false bottom.

I figured this might result in increased efficiency vs my normal process, but it didn't appear to. For normal size 5 gallon batches I plan at 75% and usually hit 75-77 for mostly-barley recipes. For this one I missed preboil gravity one point lower than planned and came it at ~73% efficiency. Does this sound like something to do with my BIAB process, or is it something to do with the 50% flaked grain bill? Could it be a result of draining at full speed? My calculated grain absorption number was about the same as always. Thanks.

 

[Bobby_M]

You should have left the false bottom in place. When you drop a bag into a cooler that just has a single point drain somewhere, the bag rests against it and every drop of liquid now has to pass through a 1/2 square inch. You can also add any kind of makeshift spacer under the bag and near the drain to keep the bag off the bottom and away from the drain, even slightly. A steamer tray, a handfull of rice hulls, a chore boy scrubby pad, glass marbles, a couple loose pieces of CPVC tubing or copper tubing, just about anything food grade and inert would work.

However, the biggest problem I think you had was conversion. Adding a small portion of boiling water at about the 60 minute mark would have boosted efficiency a touch, as would another 30 minutes of conversion time. 148F for 90 minutes is usually enough for a higher enzyme mash but your diastatic power was about 50% lower in this case.

Draining speed has zero effect on efficiency when you batch sparge.

 

[DVCNick]

To address the first issue, I just manually pulled the bag slightly away from the drain port and it drained at high speed.

As far as the diastatic power, I don't have a very high level of understanding of exactly how that works so hopefully you've identified that issue for me! Thanks. It was 5 lb of 2 row and 5 lb of flaked oats and wheat. I certainly don't mind adjusting the process a little bit as indicated for this type of grain bill in the future.... so would I have been looking at even lower efficiency if I had a typical false bottom and had to leave some liquid behind?

 

[Bobby_M]

Real simple overview. Diastatic power is the measure of total enzymes available in the mash for starch to sugar conversion. If you use 100% 2-row (or any light base malt), let's just say there was enough DP in the mash to fully convert in 70 minutes at 148 because 2 row has a DP of about 110 degrees Lintner. If you now use half as much 2 row and equal parts unmalted or non-diastatic malt such as flaked wheat or oats, you still have the same amount of starch to convert but you have an average mash DP of 55 degrees Lintner. Now that mash may take 140 minutes at 148F to fully convert. The times are temperature and grind dependent but that's how it works.