There is no problem squeezing the bag. Thats false crap spread by 3v brewers, but because their filter is the grain bed this is true for them. Your bag is your filter. It prevents any grain from entering your kettle. Plus in 3v you get sparging issues if you compress you grain bed too much.
I went down the avenue of sparging with BIAB but its a waste of time. Remember BIAB is meant to be simple. If you have capacity for full boil mash, stick to it. If you want the extra few gravity points, heat to mash out temps. Warmer temperatures allow more sugars to be suspended in your liquid. Warmer temp = greater solubility.
If you were right I would agree with you, sadly a fair fraction of the above is codswallop.
At present I am BIAB brewing and don't squeeze the bag for a couple of very good reasons
- A lot of the highest molecular weight proteins that are soluble condense at mashing temperatures, squeeze the bag and some of that white goo that comes out is high MW protein, it can react with hops products in the kettle, we want this to happen but the Highest MW protein will combine with polyphenols first and this can result in removal of the less small protein that we do want removed.
- Part of the extra stuff that comes out when you squeeze is flour, as is in fine grain, this does nothing good in the kettle, it will easily char on heating surfaces, causing flavour problems as well as reducing heat transfer.
- You can also increase the elution of Glucan gels into the wort.
The clearer the wort going to the kettle/boil the better.
Sparging particularly batch sparging the malt has its advantages, both in terms of getting the wort temperature up to around 80oC to maximise sugar solubility, and also increases efficiency. It isn't required and for simplicity sake can be omitted, provided you equipment is big enough for your batch size.
Just because a method suits your needs, that doesn't mean its the only way or that suggesting alternatives is a conspiracy by 3V brewers, or that there are other approaches that will serve someone else better.
Hez
You will probably get better results by batch sparging with 80oC water (salts and acid included), with a bag rather than a fully established filter bed (i.e. 3V system) most of the sparge water will travel around the outside rather than through the grist where it is needed. I would reserve about 2 X the grain weight for sparging, heat it to 80oC, fully cover the malt and let it steep for at least 15 minutes (30 would be better so try 20 - go on) before pulling the bag for the second time and adding the batch sparge to the kettle.
Mark