Recirculating BIAB setups

It is difficult to setup a reliably functioning recirculating BIAB without a specifically designed grain bag.

I love recirculating my wort during mashing: it provides clear wort and allows consistent temperatures and mash step automation. I also love BIAB, and use it whenever I want to shave some time off my brew day, or setup my brewery outside on a nice day, or am feeling too lazy to clean up a lot of equipment. I really want to combine the two into a recirculating BIAB system. No so much for clear wort, more for temperature stability and step mash automation. I’ll just call this style “re-BIAB” for short from here on out.

TL;DR: it proves more difficult than I imagined using a standard grain bag, but there are some steps to take to increase your success rate. The ultimate solution however is using a 400 micron bag from The Brew Bag!

All of my initial testing was done using the 210 micron mash bags from The Brew Bag that I sell in the shop, I also used a bag from wilserbrewer – it is also of very high quality, and fine mesh.

The very first time using re-BIAB I dry fired my heating element! Luckily I caught it early and could save the heating element with a stainless steel wire brush. It turns out there is such a thing as the BIAB version of a stuck mash, where the permeability of the filter (the bag in this case) is greatly reduced, forming a vacuum underneath the false bottom as the pump drains the wort out from under the mash bed. If you lift the bag off the false bottom, flow immediately returns to normal, sometimes with a sucking sound as the vacuum is released.

Brew Kettle Tri Clamp Sight Glass
The Sight Glass Manometer

There are a number of factors that I experimented with to try and resolve the problem:

  • pump flow rate
  • false bottom porosity
  • grain crush size
  • Grain rest before pumping, and,
  • the addition of rice hulls to the mash.

One key piece of equipment that I used in my experiments is a prototype sight glass that, with its opening under the false bottom, acts as a simple manometer. As the porosity of the filter decreases and the vacuum under the false bottom increases, the water level in the sight glass will fall. So here is how the experiments went – qualitative results only!

Flow rate. If you try to recirculate full bore at 15-19L/Min with your pump in this system, I can pretty much guarantee that the last thing you’ll hear before dumping the batch because it got burned is that “giant sucking sound” when you lift the bag and release the vacuum beneath – notice how heavy that bag feels now? You certainly don’t need that kind of flow rate just to maintain mash temperatures. I found that reducing the flow to about 5L/min greatly helps to minimize the stuck bag problem, but not completely! I nearly burned a batch flowing at about 6L/min. At least you can walk away relatively safely for a short time – and I even had batches that were fine throughout the entire duration! So definitely keep the pump rate on the low side.

False Bottom Porosity. I tested various false bottoms to see if increasing the porosity of the false bottom would help increase flow. I tested the standard 1.3 mm Craft Hardware false bottom, an RV2-3.5mm perforated sheet, and a custom made perforated sheet with 12mm holes and a calculated open area of almost 50%. Surprisingly, none of these helped. Even with the 12 mm hole false bottom, the system stuck again and again (I tested at higher flow rates). I could not discern any difference between the different versions.

A word here on baskets. A stainless steel basket in lieu of a mesh bag may help solve the problem, depending on the mesh size. A basket also allows drainage out the sides of the basket. Unfortunately I did not have time to acquire or make one, so I can’t say for sure but it makes sense that if there is space between the basket mesh and the kettle wall, there will always be a free return path for wort to reach the outlet, bypassing the grain. At this point I don’t plan on offering a basket product, but if you have one and use it in a re-BIAB system, please share your experience in the comments!

Grain crush size. In the forums several users suggested that a finer grain crush contributes to the problem; a very fine crush creates more powder which more easily clogs the bag. My own tests on the matter seem to support this, to some extent. I ran 3 batches crushed at .025″, .04″, and .05″ (.63mm, 1.0mm, and 1.27mm) . The finely ground batch did indeed seem to clog faster than the courser crushes, but both the .04″ and .05″ crush also created circulation problems. It may have taken a bit longer but the underlying problem was still there. Furthermore, I experienced a significant drop in mash efficiency with the .05″ crush, so I probably will stick with .04″ in the future.

Grain rest. The idea here is to mash-in with the pump and heater off, then let the system rest for 5-10 minutes while the grains absorb water. if the particles enlarge with water absorption, maybe the grain bed will be porous enough to allow sufficient flow even with the bag in place. Now, my experience here was mixed, as the first time I tried this I was convinced it helped, but the next time it did not. The theory is good, however, and I’d recommend this step if you want to give re-BIAB a try.

Rice Hulls. I’ve used them frequently in my 3v HERMS system when brewing with adjuncts or high wheat percentage grain bills, and they do help in that scenario. Unfortunately, I didn’t find them helping very much in the re-BIAB scenario. Do they make it worse? No. Are they expensive? Not at all. So go ahead and use them if you have them, especially if you are using other adjuncts or a high percentage of wheat.

So where does this leave us? I was ready to stop recommending re-BIAB completely! Until, that is, I saw that The Brew Bag started selling a BIAB bag with 400 micron mesh size – specifically made for recirculating systems. I had a few sent over from the US and got to brewing.

Good news: the 400 micron bag fixed all the problems! Using a standard grain crush (1mm) I am now able to recirculate at full flow, without rice hulls, using the standard slotted false bottom. Turns out the 210 micron bags are really just not applicable to a reBIAB system.

I would like to start supplying these 400 micron bags in the shop, but I’m just not sure how high the demand is going to be here in Europe. Do you have experience with or would you like to use a re-BIAB system? Let me know in the comments!

8 thoughts on “Recirculating BIAB setups”

  1. Hi Douglas. Thanks for sharing your experience. I learned the hard way about pump + bag.

    I got the vacuum issue and the heater became very hot, I noticed something was going on when the wort started to flood the kettle and the bag that was overhanging started to disappear from outside to be sucked into the kettle. I keep the lid closed with recirculation coming into a hermetic tri-clamp connection in the lid. The second time I let some air to get into the lid, by not closing completely. I thought that because of closed lid, the vacuum was forming. I also tried with different flown rate of the pump. It doesn’t not matter, it will happen during the 60 mash.

    Long story short I almost ruined my two heaters (I have two heaters of 2.4 kW into my SS Brewtech 38L kettle). When I read this post I realized that more people had similar experience, I was about to consider making a grain basket of stainless steel to hold the grain during the mashing. Like most of these automatic breweries like Grainfather, Robobrew have. But that seems too much work and expensive. Because there is nothing I can just buy and use it into my kettle. MY bag is from The Brew Bag, 36×43 cm.

    But since your post, I truly believe that I could get this 400µ bag! Did you start importing from the USA? Are you considering selling it in Europe? By the way you have fine products to sell, pity that I already build my own Steam Condenser, can’t thing brewing with that. I am already thinking on build a larger system, 38L is too small for higher gravity or 2x 19L kegs. I will order something from this store in the future.

    Best Regards

    • Hi Cristofaro,
      Thanks for sharing! I also thought about the Stainless steel basket, but the recirculating bag is so much simpler and cost effective. Yes I am importing them for sale in the shop, check back in about a week because they are in customs right now. They are custom made to fit our 38L and 57L kettles, same as SS Brewtech. The 10g 38L size is actually 37 x 42 cm. The heavier 400u mesh makes the whole bag less flexible so you need to make it a bit wider to fit comfortably over the kettle rim.
      Best Regards,

  2. Hi Douglas

    I am writing back since I bought the 400µ mesh from you and a few days ago I brewed with it. The bag is super strong and it looks like it will last many years easy.

    I brewed a NEIPA and the recipe consisted of 80% Pilsen malt + 10% Chit wheat malt flakes + 10% Oats flaked, total 6650 g of grains. I noticed that I would have problem quite fast. The pump flow became slow and the vacuum increased quite fast. I tried to adjust the flow but that would not help. It was quite stressing to avoid scorching the wort while keeping the temperature during mashing, still it happened to burn the wort pretty strong. I am still waiting the fermentation to complete, if that impacted too much the flavor of the beer. Did you try to recirculate using oats in your grain bill? I guess this setup is not Oats friendly. Best Regards.

    • Hi Cristofaro, sorry to hear about the brew day. I have not tried the 400 micron size bag with oats yet, maybe I will brew a NEIPA soon and give it a test. Oats and wheat are notorious for creating problems with a standard false bottom so I can imagine they are also sticky enough to cause problems for the 400 micron bag. I’m not sure if this is a problem that any amount of rice hulls can solve but that might be worth a shot. I would also reduce power to the heating element when mashing to help prevent scorching. Or maybe it requires using only periodic recirculating while standing at the kettle and stirring. Not optimal, but maybe a sacrifice to make a good NEIPA.

      • Hi Douglas. Thanks for the comments. I will buy rice hulls and give it a try for the next batch! If you have the chance of trying yourself, please keep your blog updated. I always learn something new when I read your writing. Best Regards. Cristofaro

        • Today I brewed a nice NEIPA with the recirculating BIAB 400 micron bag. The grist: 4.5kg pilsner malt, 500g flaked wheat, 500g flaked oats. The recirculation worked great and without any issues! I added the crushed grains first (pump off), let them soak for a few minutes, then added the oats and wheat. After about 4-5 minutes I started recirculating. I was able to recirculate with the ball valve full open for the whole mash. Maybe the key is the grain crush size, I crushed with the same 1mm gap that I would use for my non-BIAB setup. I would not recommend crushing finer, as one typically does with BIAB. The crush you get from your local supply shop is probably perfect.

  3. Good to hear. I wonder if the order was the main reason. I mixed all crushed grains with the oat, when I started recirculating it looks like porridge. As you described, you added the oats later, which was over the grain bed! That is a very clever idea, will follow this next time. I also use 1.0 mm gap, not finer. Two days ago I brewed a Vienna Lager and the recirculation worked perfectly. I milled again with 1.0 mm gap. For this last one I made a grain conditioning spraying water of about 2% of grain weight. I purchased rice hulls for another attempt of NEIPA, just to be safe. Thanks for the update.

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