Batch sparge BIAB efficiency

Well I dug around the forum but couldn't find the answer to the question I had regarding calculating efficiency when batch sparging with BIAB. First, here is a quick rundown of my process. I plan to ash in my 7.5 gallon kettle and then transfer the wort to a bucket. Heat my sparge water in the same kettle, rinse grains. Then return the wort to the kettle and bring to a boil.

Now for the question. Do I want to take my gravity reading and volume of just the wort (pre-sparge), or the gravity and volume of the wort after I combine it with the sparge water?

Thanks!

Thanks for this question! I had been searching for a relatively same question. I use beer smith but I can't seem to figure out how to calculate efficiency or how much to sparge using Beer Smith. I actually want to do a different technique of using a extra kettle to sparge my grains in a bucket, while keeping the wort in the 7.5 gallon kettle. Seemed more efficient to me and a lot less work.

you can take gravity readings whenever you feel necessary to monitor your progress. If you want lots of information, I would take a gravity reading of just the first collection (in your case going into the bucket) as a sort of "first runnings" number, then I would take a pre-boil gravity reading of everything once re-combined in the kettle, then take a post boil gravity reading as it is entering the fermenter and pre-pitching.
Gravity is based simply on net sugars extracted, thus really efficiency could be calculated from either the pre or post boil gravities as long as you accurately know the volume of wort from which the gravity reading was taken.

Do you plan to apply heat to the mash in the kettle? If not, you might as well mash in the bucket so that you can heat your sparge water in the kettle prior to the mash being finished. That way you just lift the grain bag out of the bucket and dunk it in the boil kettle to sparge, then add the bucket wort back in. Of course, in both cases heat retention is an issue.

The key to any efficiency calculation is accurate volume measurement. Decide how you'll measure volumes in the kettle and then you can measure that volume and sugar density at any time as long as both are measured at the same time.

Taking into consideration that the efficiency usually drops as one increases batch size, I can offer this:

I do 2.5 gallon test batches quite often using BIAB. Procedure is to mash at 1.5 qt/lb for 60 min (eg: 1.5 gallons for 4 lb grist) in one pot, heat remaining volume of water (sparge) to mashout temp in a second pot. After the mash is complete, I pull grain bag from mash pot, squeeze the hell out of it, then drop bag it into second pot with sparge volume and do a 10 minute mashout (stirring like crazy). After mashout I pull and squeeze the bag, dump the first running into the second pot, and away we go. With this method I consistently achieve 90-93% brewhouse efficiency. YMMV

Bobby_M said:

Do you plan to apply heat to the mash in the kettle? If not, you might as well mash in the bucket so that you can heat your sparge water in the kettle prior to the mash being finished. That way you just lift the grain bag out of the bucket and dunk it in the boil kettle to sparge, then add the bucket wort back in. Of course, in both cases heat retention is an issue.

The key to any efficiency calculation is accurate volume measurement. Decide how you'll measure volumes in the kettle and then you can measure that volume and sugar density at any time as long as both are measured at the same time.

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I'm not planning on having to apply heat to the kettle during the mash. I've done partial mashes in it before and it seemed to retain the heat quite well. Good point that I could just mash in the bucket, my only thought is that there is more room in the kettle to let the grains spread out. Perhaps this would get me a slightly better efficiency than if I mashed in the bucket.

I do have a way of accurately measuring the volume in both the bucket and my kettle, so no worries there. I'm thinking it might be a better idea to take my gravity/volume readings based on the first runings to avoid the possibility of the water not mixing well pre-boil, therefore throwing off the gravity reading.