Just trying to get some ideas about what influences BIAB efficiency.
Would I get a better efficiency if I: a) did the BIAB with the full amount of strike water all at once, or b) used say 80% of the water for the initial mash and then sparged with the remaining 20%? My guess is the second option has higher efficiency but Id like to hear if that is actually true or not.
If I squeezed/pressed the bag, would I get similar efficiency regardless of which method I used in the previous question?
There are two types of efficiency you need to worry about:
Conversion Efficiency: This is the amount of starch converted to sugar in your mash divided by the theoretical maximum amount of sugar obtainable from the grain. The "theoretical" maximum is actually determined by a special type of laboratory mash.
Lauter Efficiency: The amount of sugar that ends up in your boil kettle divided by the total amount of sugar that you created by conversion in the mash.
The overall mash efficiency is the conversion efficiency times the lauter efficiency.
Most efficiency problems with BIAB turn out to be conversion efficiency problems. Conversion efficiency is a function of crush (grain particle size), time, temp, pH, and agitation. Finer crushes convert faster than coarser crushes due to diffusion effects. So, you can compensate for a coarse crush by doing a longer mash in order to get closer to 100% conversion. If conversion is incomplete, and you do a hot water sparge, you may get additional conversion due to the extended time and additional agitation (same with a mash out.) Agitation helps speed up conversion by short circuiting some of the diffusion limited processes. If you have poor conversion efficiency, you cannot completely fix it with a sparge.
Lauter efficiency depends on the volume and SG of the wort retained by the grain after draining. The gravity points retained equals the volume of retained wort times the SG-1 of the retained wort. Lauter efficiency equals BK points / (retained points + BK points).
Both squeezing and sparging reduce the retained points. Squeezing by reducing the amount of retained wort. And sparging by reducing the SG of the retained wort. A thinner mash starts out with lower SG for the retained wort.
So, the answer to whether sparging or squeezing creates the higher efficiency is that you get the maximum efficiency by doing both. If you only do one or the other, it depends. A very aggressive squeeze will produce better efficiency than a low volume and/or poorly conducted sparge. A good sparge will give higher efficiency than a weak squeeze. And, a very extended gravity drain may produce an efficiency equal to a squeeze.
Which is better depends on the exact process. Some people would rather squeeze than sparge, others don't like squeezing, and either sparge and/or use an extended drain. Any and all combinations will work. It's a matter of personal preference. As long as your getting an efficiency acceptable to you, you don't need to change anything.
If you are unhappy with your efficiency, then you first need to determine whether your conversion efficiency or lauter efficiency, or both, are causing the problem. With BIAB you should be able to achieve 95% or better conversion efficiency, and 80% or better lauter efficiency. For help on diagnosing efficiency problems, check out my posts
here,
here, and
here.
Brew on