The BIAB system has grown from its roots in Australian homebrewing culture to become popular worldwide. We got advice from two brewers well steeped in the system of mashing in a bag to describe pitfalls, dispel myths, and provide guidance for those who utilize or plan to utilize a BIAB system.
John Palmer — author of How to Brew and co-author of Water
Squeeze The Bag?
There are two reasons to squeeze the bag: 1. Squeeze it a little bit to prevent it from dripping on the floor, and 2. Squeeze it quite a bit to wring out every milliliter of wort. Option 1 – A Little Bit, is never a bad idea. Option 2 – A lot, depends on the kind of grain you are mashing. The base malts and low color and caramel malts give up their extract easily, so squeezing the bag gives you retained wort instead of retained extract. Roast malts and high color caramel malts, like Special B, don’t give up their extract easily, and aggressively squeezing the grain bag will release more of the roast compounds into the wort. These compounds can taste quite harsh. Too high a wort pH can commonly lead to tannin and silicate extraction from the grain, but high pH is usually not a problem with BIAB. However, excess pressure can excrete these compounds into your wort as well, so in general, I don’t recommend squeezing the bag to wring every last drop, and in particular, I certainly don’t recommend it when you are brewing dark beers. See my article, “Mechanics and Chemistry of Steeping” in BYO, March-April 2016.
The high water to grist ratio can cause problems with the mash pH if you have high alkalinity water – and most people do. What is high alkalinity water? Look at your water report for Total Alkalinity as Calcium Carbonate. If this number is 100 ppm or greater, you alkalinity is high. If it is more than 150, then it is very high. Dark beers can often be brewed with high alkalinity water without having pH/flavor problems, but very high alkalinity often results in high mash and wort pH and harsh flavors.
If you have high or very high alkalinity water, I recommend you dilute that water 50/50 with distilled water, and/or use some acidulated malt or brewing acid (ex. lactic acid) to help neutralize the alkalinity and bring the mash pH down into the recommended range, 5.2-5.6.
I always recommend that brewers check their mash pH on a cooled sample with a pH meter at the beginning of the mash, about 5-15 minutes after mashing-in. Generally speaking, your mash pH should be between 5.2-5.6, although it can be as high as 5.8, but should not be below 5.2 or above 5.8. Staying within this range will optimize beer flavor and conversion. If your measured mash pH is 6.0 or above, you have a much higher probability of harsh flavors due to tannin and silicate extraction from the grain. Sparging with high alkalinity water will only make the problem worse. The beauty of BIAB is that it is primarily a no-sparge method, and not sparging reduces the likelihood of high pH wort.
The efficiency of any brewing process depends primarily on the water to grist ratio that you are using. Generally speaking, the efficiency of BIAB should be between 74-84% for beer OG’s between 1.040 – 1.075, lower OG having higher efficiency than high OG. Crushing the grist finer/smaller will increase efficiency by a few percent, but I really don’t recommend doing that as it will increase the fines in your wort and slow the draining from the bag. If you plan your grain bills conservatively, you should easily hit your OG target. The BIAB water retention factor, 0.25 quart per pound of grain, is typically half that of a standard mash 0.5 quart per pound. In liters and kilograms, these numbers are roughly 0.5 liter per kilogram and 1 liter per kilogram. The weight of the grain pressing on the bag naturally drains more wort than a standard lauter tun, and you therefore get more wort from the same size mash, all else being equal.
Here’s an example of planning a BIAB grainbill: Let’s say you want to collect 7 gallons of wort to make 6 gallons of 1.055 wort into the fermenter. We’ll assume our efficiency is about 80%, given that it’s about halfway in the range stated above. The target gravity for the 7 gallons of wort from the BIAB mash is 6 x 55 / 7 = 47 or 1.047. The maximum extract we can typically get from a weight of grain is 80% by weight, which is 37 PPG (points per pound per gallon) or 309 PKL (points per kilogram per liter). Multiplying these numbers by our brewing efficiency of 80% gives us an anticipated yield of 29.6 PPG or 247 PKL. To calculate the amount of grain required, divide the total gravity points (OG x Volume) by this anticipated yield. 6 x 55 = 330 / 29.6 = 11.15 pounds. In kilograms and liters, this would be 22.7 x 55 = 1248.5 / 247 = 5 kilograms, which is the same as 11.15 pounds.
The wort retention is 0.25 quart per pound, so for 11.15 pounds, about 2.8 quarts will be retained. This means that you would want to mash in with 7 gallons plus 2.8 quarts, or about 31 quarts. This volume will give you a water to grist ratio of 2.8 qts./lb. and should give you the 1.047 boil gravity by my calculations.
In general, wort clarity coming out of the mash and into the boil is not a concern. Wort turbidity (essentially the opposite of clarity) has been argued back and forth for years. On the one hand, there is a case for shorter flavor stability for a beer that is not separated from the trub during fermentation, and not adequately clarified before packaging, due to excess lipids that can oxidize and generate off-flavors. On the other hand, a highly clarified wort doesn’t provide sufficient nutrients to the yeast, which will cause them to need more aeration so they can synthesize what they need, and will result in a less healthy fermentation and more fermentation byproducts. Note that in one case we are talking about turbid beer being bad, and in the other we are talking about turbid wort being good. Where is the real conflict?
In fact, recent studies on wort turbidity, wort zinc, and lipid content indicate that turbid wort generally produces a better fermentation and a better tasting beer. However, once that fermentation is done, good trub separation is necessary to promote flavor stability. Get the beer out of the fermentor and away from the trub to reduce oxidation. Fining agents such as isinglass and gelatin can help in this regard. And remember, all things in moderation – just because some trub into the fermenter is good for yeast health, doesn’t mean that lots of trub is better. Don’t go overboard with this. Bottom line: Don’t worry about wort clarity into the boil.
Advanced BIAB Techniques
The beauty of BIAB is that it is a no-sparge method. Sparging in a traditional lauter tun system can get a higher percentage of the total extract in the grain, but that is not necessary on the homebrewing scale. You can readily achieve good efficiency by increasing the water to grist ratio as described here and in the latest (4th) edition of How To Brew. If you have a high alkalinity problem with your water, you may want to use a more typical water to grist ratio of 1.5-2 quarts per lbs. (3-4 liters per kg) to conduct the mash, and then add the rest of the water at the end. At the end of the typical 1 hour mash, you would add the remaining couple gallons, stir to get everything homogenous, let it rest a few minutes, and then drain as usual. The idea is that you are optimizing the pH conditions for the mash at the lower water to grist ratio, and then adding more water later to get your total boil volume and gravity, without sparging.
BIAB is not limited to single temperature rests. Many brewers want to maximize the fermentability of their wort by doing both a beta and alpha amylase rest at 145°F (62.5°C) and 158°F (70°C), respectively. If you are mashing in a kettle, simply raise the bag off the bottom and stir while you are heating from the stove or burner. If you are mashing in a cooler, then simply start the mash at a lower water to grist ratio, such as 1.25 or 1.5 quarts per lbs., (2.5-3 liters per kg) and use infusions of hot or boiling water to raise the temperature to the next rest. Be sure to add the hot water slowly and stir during to reduce the stress on the enzymes. Decoction is another good way to conduct multiple temperature rests. Decoction sounds intimidating, but it is really quite easy. Scooping out the grain with a large strainer and leaving most of the liquid behind preserves the enzymes in the mash. Bring the decoction to a boil in a separate pot or kettle, and add it back to the mash. The boiling hot grain needs to be added slowly and stirred while adding just like the infusions.
Brew in a bag (or basket) might actually be the original home brewing method from thousands of years ago, and traditional mash and lauter tuns may actually be new-fangled contraptions to enable large scale brewing in the relatively recent past centuries. Therefore, embrace this new-old method and don’t be afraid to adapt it to modern brewing.
Rex Slagel — Founder/Owner of The Brew Bag®
The biggest question is whether to squeeze the bag or not. My advice: Squeeze — leave no wort behind. Excess tannins taste astringent and generally result from over-sparging when the pH rises above 5.8 at mash temps. When full volume mashing (as occurs in BIAB) followed by no sparge, the pH doesn’t change.
The other misconception is beer clarity, I don’t think there are clarity concerns when using a fabric filter — it’s just a filter. I believe there’s not enough information to support the controversy about this issue. Brewers have always had clarity issues, but when they switch to using a fabric filter and have a cloudy beer they point to the obvious variable — without true controls to rationalize the outcome. I’ve never sparged and always squeezed and I’ll refer to the many awards using this process.
One special consideration that I feel brewers should address when attempting their first BIAB is their kettle size. A good rule of thumb is 2.5 times batch size = kettle volume. A 10-gallon (38-L) kettle will allow a 5-gallon (19-L) batch, but when pushing the volume up to retain that water-to-grain ratio for high gravity beers, the extra space is beneficial.
A fellow brewer and I tracked 150 or so batches and we both averaged 78.5% extract efficiency for our mashes. That means reduced grain bills off of the 72% to 74% efficiency typical of sparge results. A hidden factor is the amount of wort tossed away into the compost or garbage when sparging. Using a fabric filter and no sparge, all of that wort is transferred to the boil kettle so the efficiency is 100% of the available wort — leave no wort behind.
One technique I’ve utilized with success is a modified parti-gyle. You can lift the grain out of the kettle and drop it into a cooler. With a few additional pounds of grain you can double your volume by only adding the boil time of the second batch. The first is boiling while the second is mashing. And by changing the grain addition you can create a porter from a Kölsch, or whatever you choose.