Did my first AG batch last Sunday using BIAB. Making the switch cost me much less than $10.

Cost of bag (pre-made, purchased from LHBS): $7
Cost of 13lbs two row: $19.50

What I would have spent on 9lbs of extract: $33

So switching from extract to all grain actually saved me $6.50 in the first batch.

The process also worked almost perfectly, with the only exception being I got my strike water a bit too hot, and even with the heat off and the lid off and holding ice packs on the sides of the pot, I was not able to get the mash temp down from 156F to my target 154F for about 30 mins. My recommendation would be to err on the side of too cool because (in my case at least) you can always add direct heat to get the temp up, but getting it down quickly is extremely difficult.

Regarding pots, I would say the bigger the better. I have a 10 gallon pot and just barely had room for 7.5 gallons of water and 14.2 lbs of grain. Which begs the question: do I really need to have all my water in the pot when I start, or can I mash with less water and then top up before the boil? I really can't think of a reason why topping up wouldn't work, but admittedly, I am new at this. Is the problem topping up with cool water? I could certainly top up with hot water since I brew on the stove and can easily heat up a two gallon pot on another burner. Leaving room in the pot during the mash and then topping up would also enable me to fine tune my temperature.

Finally, one note regarding efficiency: I was able to get 77% extraction. My LHBS recommended running the grain through the mill twice, which I gladly had them do. I do not have a control batch made with a single pass through the mill, so I can't comment on what effect the second pass had on efficiency. Unless I'm feeling nerdy and do a control batch, I will likely never know because I had no issues with bits of grain passing through my bag.

I did My first BIAB yesterday and have a couple of observations and a question:

strike water calculations have to be spot on because with that volume of water you cant recalculate "on the fly" like you can in a much thicker mash . I use an android app called "mash" that is really easy to use and actually works but I can see how you could go wrong by being a degree out.

The process is _really_ quick and simple . I was atually at a loss as to what I could do with the rest of my day.

TB: should you squeeze the bag at all? I gave my bag what I thought was a tiny squeeze but when I weighed the spent grain found the total weight was only 6kg on a 4.5kg grain bill. By my calculations that means about .33L per kilo water uptake, considerably lower than anything that I have read on this thread.
The wort seemed a little tannic post boil but that may have been partially to do with the oak chip tea that I threw in at the end of the boil.

Do you know where the 120 microns came from? Is it just based on trial and error (sometimes it's the best way!) or is it based on some calculations?

I am thinking of using the bag but putting it in a stainless steel strainer with an added mesh filter of '?' microns. This would help me removing the bag and prevent the bag from touching the bottom of the kettle.

I read that somewhere:
"In a study in a German brewery (2), hot trub particles varied in size from 30 to 80 microns."

Strike Temps - yep, aiming to err on the low side is what we tell people when we give BIAB demonstrations at Grain & Grape. One of the beauties of BIAB is that your mash tun is directly fired... adding heat is easy. Step mashing is easy too.

Topping up - no reason not to. It will reduce your efficiency a little bit though. The reason BIAB uses all the water up front is not because its necessary from a mashing perspective.... its its own reason. No need for a separate vessel to heat water in, no need to make additions. all the water at once was simply a result of trying to make the method as simple as possible and keep it to just the one pot required. If you are willing to do a little extra.... you can top up via dropping your bag into a bucket, pouring the top up water (hot or cold) onto it and giving it a stir up. viola... sparge and efficiencies up at the 80% level.

Me - i think that in a 40L pot its only necessary for bigger beers. Most guys i know with 40L pots manage the vast majority of their brews at full volume and do it that way because its easier. But do what works for you, theres no reason why not.

Strike temps - see above. Aim a little low and all the worry goes away. Me, I get my strike water to 2°C above my desired mash temp and mash in... that usually gets me either on target or a touch low.

Bag Squeezing - I do. I give the bag a firm squeeze once its stopped dripping of its own accord. Usually gets me an extra litre or so of wort and I'm not a beliver that a bit of squeezing of the mash (in a bag or a tun) results in tannic wort.

Wort lost to grain - you cant tell (simply) the way you measured. You need to measure your actual liquid levels to be sure. Your 6kg isn't the liquid absorbed plus the 4.5kg of grain. Remember, if things went as you planned them, you left the vast majority of the mass of that 4.5kg of grain behind in the pot - as sugar. Most base grains are something around 80% extract and you probably managed to get 75% of that to stay in your kettle.... so you left .75x.80x4.5=2.7kg of that grain in the pot. Which means if your spent grain weighed 6kg then 1.8kg was husk and junk left over from the grain and 4.2 (ish) kg was absorbed liquid. Thats about 4L in volume terms, which is actually a grain absorption rate (as its usually measured) of 0.9L/kg of starting grist. which is in fact a little more than usual for BIAB. I'd let your bag drain a bit longer, which would get you to around 0.75 and a bit of modest squeezing will get you down even further.

I dont know where 120 microns came from... and i actually dont know the 120 microns to which you refer? Did some one (did I?) measure the size of the gap in the voile material and say it was 120 microns?

I dont think I actually know the density of the weave on my BIAB bag - I dont really care to know. I describe it as a "very fine mesh" it should be on the order of a pair of ladies nylons, the mesh in a french press coffe filter, the mesh in a "fine" hop bag. If you tip water into it, it would fall straight through with basically no resistance, sand wouldn't fall through, flour would if you jiggle it for long enough. Basically, bordering, but not at the point where it stops being mesh and starts just being cloth. The bag material was first worked out by a smart guy walking into a fabric shop and thinking to himself that "this stuff looks just about right" and then later by dozens of people trying to come up with something better, and failing.

Bag inside another perforated pot - if you like. A few brewers I know of do a similar thing. It works pefectly well. I've tried it and personally find the bag a hell of a lot easier to handle without the pot. And then i have to actually have another pot; and then clean another pot; and by then I might as well just have a multi vessel system.... so its not something that i think is a great idea, but it certainly works OK.

Mesh to strain out hot break..... more or less doesn't work. If the mesh is actually fine enough to filter it out, then it will more or less instantly clog up with break and liquid will go nowhere. The filters that are able to effectively filter break are all depth filters. Grain beds, hop backs - all rely on 3 dimensional depth filtration, not surface filtration which is what you get with a mesh.

You can do it - but be prepared to wait quite a while for the liquid to come out of your mesh filter if you make it fine enough to do the job you want it to.

And as I have repeatedly said.... you dont need it. the break that makes it through the bag, just comes out in the boil like all the other break.

I suggest you try BIAB as detailed in this thread, lots of thought and lots of brewing has gone into making it just about the easiest way to skin this particular cat. If for some reason it doesn't give you results you are happy with, then try modifying it. Of course if you feel the irresistable urge to tinker with it.. why the hell not? If you give it a little thought, virtually anything you come up with can be made to work - after that its just about your personal preferences.

TB

1.069 target OG, 1.073 actual, so it was on the big side. I also seem to lose quite a bit of volume to evaporation. My pre-boil gravity was within a point of my target, but my post-boil volume was lower/gravity was higher than expected. I suspect living at 6300 feet in a dry climate contributes to that. I'll need to figure out how to adjust my recipes to compensate.

yeah, 40L is too small if you plan on beers like that very often - or you do the sparge or top up thing. evaporation is just about working out what you get and reverse engineering how much to start with. Couple of brews and you'll have it sorted.