Brewing Process Logic: Everything You Want to Know About BIAB

How does changing the filter affect the brewing steps for home brewers?

The use of fabrics for wort filtering is now old news that has been delivered to the home brew community’s doorstep as “Brew In A Bag”.

In the brewing community, some still believe that using this type of filter creates changes in the home brew process that deviate too far from the conventional three vessel method. It is considered common knowledge that the only sure way to transfer the highest volume of sugar into the boil kettle is by sparging, but brewers who use a removable fabric filter are discovering that this is simply not the case.

What is not fully understood by old and new brewers alike (yet) is that every step in mashing prior to releasing the wort into the boil kettle is predicated on the type of pickup used. Before we compare the sequence of mashing steps used by home brewers, consider that any type of fluid filter is designed to allow passage of liquid while holding back particles larger than “x” micron.

False Bottoms & the Flow of Wort

Not to get ahead of ourselves, let’s first talk about wort — aka sugar water — and the current list of pickups / manifolds that include the stainless braided cord which is typically used for bathroom water line protection, #18 or #20 mesh screen formed around copper pipe and fitted to the ball valve, drilled or cut PVC or copper pipe, and a metal drilled or stamped plate called a false bottom. All of these are bottom-resting pickups and are designed to hold back and / or keep the grain from passing into the kettle.

To further ensure the flow of wort, home brewers often use a combination of a false bottom and another pick up. This adds “dead space” volume to the water equation. ‘Dead space’ is code for lost wort, which is trapped beneath the false bottom and is above the pickup – this wort never makes into the tun.

Prior to the introduction of fabric, the grain bed has always been used as the wort filter. The manifold / pickup is the device used to allow the wort to flow out of the mash tun and into the boil kettle — the pickup is the thing that clogs.

In 3V brewing using fly or modified fly sparging, emphasis is placed on protecting the integrity of the bed by not adding sparge water to fast or in too great of volume and SLOWLY releasing wort out of the mash tun.

Even in batch sparging the pickup can clog if the bed is not allowed to settle and / or the ball valve is not used to control the out-flow of wort.

The use of a removable fabric filter eliminates the logic of processes associated with using the grain bed as the filter… In doing so, and because there is no fear of a stuck sparge, the endosperm can be ground to near flour.

This exposes substantially more surface area to enzymatic action, reduces time to convert and aides in more complete conversion. And there is no deadspace when using a fabric filter, so 100% of the wort can be collected. This also means that the water calculated for dead space loss is removed so the sugars are less diluted.

How do brewers strain the grain husk, unmilled grain bits, and hops out of the boil kettle? And why do they do this?

To better understand the differences in manifold/pickups, and because every article I’ve read provides no specific detail about the process decisions driven by the type of pickup selected, I encourage you to continue reading to discover this answer. This article is meant to provide that information by listing those processes and their results by comparing the use of a fabric filter to the standard pickup driven methods. Using this information, you can decide what’s right for you. Traditional method information will be given first and the fabric filter information will follow in italics.

What are we after and how do we get it?

Using mostly tap water, creating wort is simply done by putting milled grain in a mash tun and adding hot water. Getting the maximum volume of converted sugars contained therein out of the tun is a bit more complicated.

“Success” is measured as kettle efficiency, which is commonly known as the pre-boil gravity. The hydrometer reading indicates the percentage of potential sugars available from mashing any given grain bill that make it into the boil kettle. Efficiency is relative to and dependent on how we get the wort out of the mash tun.

Until the use of a fabric filter was discovered by the Aussies, home brewers relied on all sorts of screen or drilled pipe configurations to pick up the sediment-bed filtered wort. All of them attach to a drain at the bottom of the mash tun. The drain is controlled by a ball valve which regulates the outflow of wort. Without the ball valve the wort moves through the grain bed too quickly and causes channeling and incomplete transfer of sugar. Because of the fast flow the wort drags particulates into the pickup openings causing a clog, or stuck sparge.

In fact, every “how to” on brewing I’ve read, listened to, or watched points out how to avoid a stuck sparge. This means the information being passed down from knowledgeable sources recognize that the type of pickups being used by home brewers are common, and they clog.

So if the pickup gets clogged and the grain, mill setting, and mash/lauter process is built around avoiding that issue – would an alternative allow changes to the steps currently used, and what would be the results?

The Logic of Pickups

Understanding the differences in wort pickups and their impact on the processes that lead to the collection of wort is the purpose of this article. The adage “a chain is only as strong as its weakest link” is true of home brewing as well.

In order to prevent a clog, or stuck sparge, there are considerations that go all the way back up the process chain and start at the choice of grain and mill gap setting. Too coarse a grind and conversion suffers, too fine and the standard screen or manifold clogs. And without adding rice hulls in every mash, the pickup also defines the styles you can brew, and ultimately the beer you drink. In addition, the pickup also determines the method of sparging, which dictates the time it takes to get the wort out of the tun, and the length of the brew day.

An urban myth is that slow sparging aids efficiency. So let’s be clear, and this is the rationale for the use of a fabric filter for all methods of brewing—sparging has no impact on enzymatic starch conversion. Once converted, and all things being equal (meaning measured gravity in the kettle) the process employed to separate wort from grain is inconsequential.

Are sugars left behind in the grain using a fabric filter? – Yes. Are they left behind when sparging? – Yes. Is efficiency comparable or better when using a fabric filter? – Yes. Do fabric filters clog? – Never. Can you batch sparge using a fabric filter? – Yes. Can you fly sparge using a fabric filter? – Yes.

We’re talking about a change in the filter utilized – not a change to the extraction process. By using a fabric filter the processes can be changed – or not, that’s up to you.

It’s true – size matters!

What if the endosperm bits in the mash temp water were completely surrounded by free floating enzymes and channeling or a slow or stuck sparge was never considered?

To avoid a stuck sparge and get the highest percentage of sugar from the wort into the kettle, brewers have been taught that slow consistent sparging and drainage gets the job done – and it does. However, that process was developed because sparging too fast clogged the screen or manifold pickup, or created channels in the grain bed that left who-knows-how-much-sugar behind, or it compacted the bed and stopped or slowed flow.

Because they are generally handmade and not standardized, a pickup manifold made of copper or PVC does not have a consistent number of openings of equal size to accurately compare one to another, so cut at 0.25” or drilled at 3/16”, I’ll guess the total square inches either way is less than ten. A braided cord cut open and laid flat provides a pick-up surface area of about 24 square inches.

The fabric filter is generally made from polyester multifilament fabric called Voile. The openings in the fabric are ~210 microns which is 0.0083 inches and is equal to #70 mesh. The amount of fabric used for just a twenty quart kettle is no less than 1,000 square inches, over 2,000 for a sixty quart and surpasses 3,000 when used in a common forty-ish quart cooler. Using polyester straps as reinforcement the bag can hold up to four-hundred pounds.

Comparing Different Filters & Processes

So, after all that, we’ll start this filter and process comparison by reviewing the most common methods of moving wort from the mash tun to the boil kettle. The facts about using a fabric filter are in italics beneath each paragraph.

Lautering

Lautering is the overall process in brewing beer by which the wort is separated from the residual grain using water. Lautering usually consists of 3 steps: mash out, recirculation, and sparging.

In a conventional three-vessel gravity or pump driven homebrew setup using a false bottom and/or manifold pickup, all three of these steps are employed. Remember that the grain bed is the filter and holds the much-desired sugary wort until washed out.

When Using a Fabric Filter — A fabric filter is the link that allows these three individual steps to be combined into one vessel.

Mashing Out

Mashing out requires heating the mash to a temperature of 168°. It is accomplished by either adding increasingly hotter water in measured amounts to the mash tun and stirring, or if the mash has a water to grain ratio of 1.5 to 2, by heating the mash in the kettle and stirring. In controlled brewing systems, this is done to stop enzymatic conversion by denaturing enzymes, which stops conversion of starches and sets the sugar profile. The sugar profile determines the percentage of yeast attenuation (a factor most valuable to large volume breweries, but relevant to all who care to monitor), mouth feel, ABV, and fermentability.

The hot water also makes the mash more viscous, thereby allowing the wort to flow through the openings in the PVC, copper manifold or mesh cord. This step is particularly important with a thick mash where the water to grain ratio is ~1.25 to 1.50, or when using gelatinous non-hulled grains like wheat or rye, which can easily clog the pickup, or create a gelatinous “shelf” which slows the flow water through the bed. Typically when mashing with gelatinous grains, rice hulls are added to make the grain bed more porous. This prevents channeling and allows the sparge water/wort to flow evenly through the grain bed and out of the drain pulling sugar with it.

Based on inconsistent system design amongst home brewers and varying times to complete this step, mashing out is not confirmed as necessary. Rather than a noticeable difference in attenuation or taste due to setting of the sugar profile, it may be driven more by the positive flow of wort and fear of a stuck sparge.

When Using a Fabric Filter — When using a removable fabric filter, and since there is no time lag as a result of sparging, the mash out is provided for (even though it may not be needed) at the end of the mash as the bag is lifted and heat is applied to the kettle for the boil. In addition, the higher water to grain ratio in full volume mashing allows the wort to quickly wash off the grain and into the kettle, making the need for increased fluidity via sparging or heating a non-essential step.

Recirculation:

Recirculation is simply done by releasing wort through the ball valve and pouring it back onto the top of the grain bed. It can be done when the mash is active or finished and in conjunction with sparging. It can be intermittent, continuous with a pump, or manual.

The purpose of recirculation can be twofold. The first is to re-filter the initial draw off because it contains grain husk particulates that cause cloudiness. This draw off also serves to “set” the grain bed around the pickups and prevents clogging when the sparge begins. Because of the sediment bed filtering effect, particulates higher in the grain bed do not pass through to the pickup.

The second reason to recirculate is temperature control during the mash, or to raise the temperature when mashing out. This process generally requires a pump and is accomplished by carefully controlling the flow of wort out of the mash tun and passing it through a sealed heating element unit and back on top of the grain bed. Some brewers state that efficiency is maximized by this process because the grain is being continuously “tumbled” (stirred) which promotes greater water to grain frictional contact.

When Using a Fabric Filter — Using one vessel and a fabric filter, temperature is controlled by external insulation of the vessel either by using a cooler or by wrapping the kettle. Using the principle of thermal mass variation, the mash temperature is slow to change. Recirculation using a brew bag does not create any problems except perhaps when using a keggle. This is due to the narrow height of the grain bed that slows the flow of the wort to the bottom of the vessel. Unless adjusted, too fast an outflow may compact the grain in the bag and cause a flow rate pick up problem.

Because the fabric filter does not clog, efficiency is maximized through grinding the grain finer – as low as .025 – (maybe finer, but as of this writing no evidence is available.) This near flouring of the grain also ensures very high endosperm surface area to water contact and enables swift and complete conversion. Since the full volume of water is used as the mash water, there is no need to sparge when using a fabric filter. This also leaves the pH unchanged and the possibility of excess tannin production is null.

Sparging:

Sparging is defined as washing the sugars out of the grain bed. This is done by heating the proper amount of water to 168° and adding it to the top of the mash tun. The water drains through the grain bed, past the bottom mounted false bottom/pickup and out into the boil kettle.

Common to all methods, the final boil volume of wort is determined by the size of the kettle and the tun. Accurate water calculations are needed to maximize starch conversion, while considering the gravity and wort volume into the kettle. The goal when sparging is to leave the smallest quantity of lowest gravity wort in the tun. There are two common methods of sparging a grain bed.

Fly Sparging: Fly sparging is accomplished by trickling hot water across the bed in a slow delicate manner. Acting like a sediment filter from top to bottom, the graduated levels of grain compaction allow the sparge water / wort to pass, but prevent grain particles at lower levels from seeping through the pickup and into the boil kettle. It can be done with a pressure driven whirling arm or by building a PVC or copper pipe pathway that has been slit or drilled and is installed inside the lid of the tun or rests on top of the vessel. This method of sparging can take sixty to ninety minutes and unless automated, demands constant attention. Generally brewers begin this process by recirculating the initial two to three quarts of run off until clear.

Batch Sparging: Batch sparging is another method commonly used by 3V brewers. It is done by adding a measured volume of water to the mash tun after the initial mash water (now wort) has been drawn out of the tun. Batch sparging is a two (or more) step process and in addition to the draining the first running can take twenty to thirty minutes. It also requires constant attention with the initial recirculation process the same as fly sparging. I believe this technique was the gateway to full volume mashing as the addition of the sparge water after the initial draw off is literally dumped onto the grain bed and stirred. This probably left someone thinking “why not add all the water at once, and drain once”? In addition to the grain bed as the filtering component, I’ll throw this in as an aside. When using a false bottom, braided cord, or screen, brewers take such care to set the bed and clarify the wort by recirculating and then just toss the hops in the boil kettle with no filter. That’s kind of like shaking an Etch-a-Sketch to draw a new picture! However, some do use a hop spider to filter the hops out of the wort, which prevents clogging the pickup or reduces trub in the fermenter — and the spider is generally made with a similar material as a brew bag. Hop spider on the left – The Brew Bag® with copper spreader on the right.

So Now We Have To Choose?

Unlike fly sparging where the decrease in gravity through progressive dilution of the wort by the sparge water can be measured both at the tun valve and in the kettle, batch sparging is sort of “all in”. After draining the first run, fifty-percent or so of the total water is added to the mash tun all at once – which fully dilutes that volume to a set gravity. Because it can be measured and proportionately combined with the fixed gravity and volume transferred to the kettle from the first running, adjusting the first running gravity that will become the pre-boil gravity is now based on the set gravity in both.

In all cases, unless the sparge water pH is “OK” as is, or conditioned to levels matching the mash tun, it progressively changes both the mash wort and boil kettle ph. A pH above 6 can cause additional non-typical extraction of polyphenols, which create tannins and silicates, adding to astringency levels and potentially a bitter tasting beer. (raise your hand if you can identify tannins in your beer)

When using a fabric filter and the full volume of mash water without sparging, the gravity is set when the mash is complete – unless adjusting for volume in the kettle or the fermenter – it is never diluted. In addition the pH is fixed in both the mash tun and the kettle. The entire sparge process can be eliminated, saving time, effort, equipment and energy expense. The use of one kettle, one burner, and one bag with no mash out produces comparable results to sparging.

What are the macro-level differences when using a fabric filter compared to the traditional three-vessel sediment filter method and pick up?

The fundamental difference is that by eliminating the grain bed as the primary filter, the manifold / pickup can be removed without the fear of a stuck sparge. Now, instead of establishing and protecting the grain bed as the sediment filter the water to grain ratio and finer grind can drive conversion and efficiency into the boil kettle.

Because of the major differences in systems and thus steps, let’s start at the beginning from an architectural perspective.

Setting up either a three vessel (3V) system, or a one kettle BIAB requires consideration of space, time, and equipment relative to the brewers desired volume of finished beer. This can vary from one gallon to thirty, or more. And yes, voile fabric filters with polyester reinforced straps can handle thirty-gallon batches.

Space:

Space for brewing is relative to living space, or not, as some brewers consider brewing space more valuable than living space. So whatever your priorities, 3V systems require horizontal space, of at least 60” and 20” width. Some systems are tiered and some are flat, but the space requirement is the same except that the top tier of the three tier stand with the kettle on top may require a ladder to reach as it could be over 70”. Tiered set ups do not require pumps (but they can be utilized), and horizontal stands must have pumps.

When Using a Fabric Filter — Fabric filter brewing needs only space on the stove for the kettle, or if you’re brewing outside using another heat source, space for the burner stand with the kettle on top. That’s generally 20” L x 20″ W x 40″ H or so inclusive of the kettle height.

Time:

Time is a valuable consideration for everyone including home brewers. The difference between the two systems here is significant. See the chart below for comparisons, but dependent on style of beer, brewer preference for mouth feel (mash time), complexity of flavor (boil time), and equipment set up (3V or BIAB), mashing and boiling for both 3V and BIAB are generally sixty to ninety minutes each.

When Using a Fabric Filter — But, because the BIAB method allows finer grist, conversion can be complete at thirty to forty-five minutes. As of this writing I have completed three on-target batches at forty-five minutes, but since my mill is pre-set at 0.045, I cannot grind any finer until the new adjustable mill arrives. BIAB brewers commonly mill at 0.025 and convert in thirty to forty-five minutes.

The 3V method requires sparging, so depending on setup and preference this step can take twenty to ninety minutes.

When Using a Fabric Filter — BIAB fabric filter is a no sparge method, so that’s 0 minutes. No chill is 0 minutes. (did he say no-chill?)

Time & Space Considerations 3V Setup BIAB Setup Space 60” x 20” x 70” 20” x 20” x 40” – less on stovetop Mash (in minutes) 60-90 30-60 Sparge (in minutes) 20-90 -0- Boil (in minutes) 60-90 60-90 Chilling (in minutes) 0-10-30 0-10-30 Set up – Clean Up – Minutes 60-90 30-60 Total Time 3.5 – 6 hours 2.25 (stovetop) – 4 hours Cost Considerations: Stands & Kettles 3V Setup, 2 Burners & Kettles (no pump) BIAB Setup, Stove Top, Only Bag, Outdoor $400 – $2,000 $30 – $300

Brewing Equipment:

Equipment for a typical 3V set up includes three vessels, one of which could be a plastic cooler with the other two metal, or all metal. There can be two or three burners and either the propane or gas supply is split or individual, so one to three propane tanks or one gas line. As described previously, the stand is horizontal or tiered in three levels and is made of wood or metal. If homemade, a 3V stand can be built with scrap material, or if purchased, can range from $150 or so to $1,000 or more. This does not consider valves, pumps, hoses, chiller, fermenters, or any other preferred brewing equipment you may need.

In any case where open flame, boiling temperatures and flammables are present, safety is absolute, so a stable setup is critical.

When Using a Fabric Filter — Because the strike water, mash, and boil vessel are the same, only one vessel and a combined burner and stand are needed. Many brewers use the burner stand as their entire outdoor set up by simply placing the kettle on top. Although, without a pump this makes transferring to the fermenter difficult, as the height does not allow gravity feed to standard fermenters, however no-chill cubes make this a no hassle reality. The typical burner stand combination cost can range from about $30 to $100.

If brewing on the stove, the stand cost is eliminated, so the cost is limited to a vessel and a bag. Bags can be homemade for as little as $5. Home brew shops carry nylon bags that are generally one-size-fits-all for $3 to $7, or a custom bag can be purchased for about $30. A bag made of polyester voile will last beyond fifty uses, so the cost per brew decreases with each use to less than $0.60. You can find bags at www.brewinabag.com

Steps and Process

Depending on the set up, 3V brewing requires heating the strike water to temp in the upper tier or third vessel, moving the strike water to the tun, then adding the grain to the tun, stirring well and left to mash. If the setup is horizontal and has three burners the strike water is heated in the same vessel that will contain the mash. Additional water may need to be added to the third vessel and heated for sparging / mash out.

When Using a Fabric Filter — Using a fabric filter and one vessel, the full volume of strike water is heated to temperature, the bag is inserted, and the milled grain is added. The volume of strike water is easily calculated using only four numbers. Fermenter volume + grain absorption + evaporation + trub loss.

Fermenter volume is the amount of wort that will be transferred to the vessel prior to racking off to secondary or final carbonation container. Grain absorption is ten to twelve ounces AFTER squeezing the bag, or sixteen to eighteen if you don’t squeeze — but squeezing is recommended. Evaporation is the amount lost during the entire heat up, boil, and cool down and should be measured by every brewer based on elevation and kettle size by testing with water. Trub loss is the amount lost in the mash tun and fermenter.

After adding grain, the mash is stirred well and the kettle is insulated with the lid in place. Because of the high water to grain ratio and finer grist, maximum conversion occurs in less time without further stirring or recirculation. Those who do not attain efficiencies in the mid-70’s to mid’80’s using a fabric filter have generally relied on 3V protocol for WTGR ratio, sparging, and mill setting, or have a pH or water volume equation issue.

When the mash is complete:

3V brewers confirm the sparge water temperature of 168° and begin either batch or fly sparging. An accurate final pre-boil gravity reading can not not taken because the wort is still concentrated in the tun, has not been diluted by sparging to the boil volume, and based on grain bed porosity and grain bill, the sugar transfer to kettle will not be consistent over the sparge. To avoid over sparging, meaning gravity from the tun is less than 1.010, 3V brewers intermittently measure gravity at the valve as wort flows into the boil kettle and predict total volume.

When Using a Fabric Filter — BIAB method uses the full volume of water, so mash conversion is checked with a refractometer by stirring the wort and taking a sample with a pipette at any time during the mash. Once measured and accepted as complete, the bag is lifted by hand, or by pulley and hook and left to drain and/or squeezed to release matching gravity volume into the kettle. Heating to boil then begins.

Squeezing the bag of grain and tannins are not synonymous. Excerpted and paraphrased from the books “Water – A Comprehensive Guide for Brewers” and “Malt – A Practical Guide From Field to Brewhouse”: Tannins, a subset of polyphenols, are present in grain husks and cell walls. They are released at mash temps and bind with proteins to form haze. In conjunction with a pH above 6, excess tannins are extracted and impart an astringent flavor – they cannot be produced by pressure.

3V brewers continue with the sparge.

When Using a Fabric Filter — Once the boil is achieved, many BIAB brewers use their bag as a hop filter. This can be done by simply emptying the bag, rinsing, adding hops and suspending in the kettle. A copper spreader or weight that is wort neutral will be added to keep the bag from floating. The spreader keeps the bag open and allows the hops to free-float, as if there was no filter in place.

3V brewers now begin to heat the wort to boil.

When Using a Fabric Filter — Fabric filter brewers chill, or not, and transfer the wort to the fermenter, clean up and have a home brew.

Once you decide which method is right for you, the steps after the wort hits the boil kettle in both methods are the same. The objective in both methods is to make sugar water from grain, ferment it, and say Ahhh!

8 BIAB Urban Myths Resolved

1. BIAB is less efficient

Experiments by Troester and Briggs have proven that water to grain ratio (WTGR) of 2.6 per lb. produces higher brewhouse efficiency – while conversion is the same as a thick mash. Above all else, these findings provide substantiation that conversion is similar in both methods.

Getting the sugars into the boil kettle is what matters. Interestingly, Troester states “Brewers that don’t mill their own grain will not be able to affect the tightness of the crush will have to accept lower conversion efficiencies or ensure that the mash has enough time and “strength” to achieve an acceptable conversion of the starches. If the mill gap spacing can be controlled the conversion efficiency can be improved through a tighter crush. But at some point the crush might be too tight for a reasonable run-off speed.”¹

Here, again, as provided by an industry expert, {reasonable run-off speed}, aka the “stuck sparge” is recognized in conjunction with “conversion efficiency can be improved through a tighter crush.” These experiments were conducted prior to the availability of the fabric filter, or likely, the results would be expanded to include this differential.

Grain bills for 3V recipes now weigh more than BIAB recipes and fabric filter users are reporting increases in boil kettle efficiencies. This is due to the use of a non-clogging fabric filter that allows mill settings as low as 0.025. For the home brewer, this is recognition of simple science – greater exposure of the endosperm enables conversion at levels only experienced by major breweries. In addition, time to convert is less, more complete conversion is documented, and therefore each session requires less grain and less time for the home brewer.

From a recent FB post by a BIABer:

“I always adjust any recipe I get from BYO or from HBT (or any other source) and modify it to fit the efficiency of my system. That generally means reducing the grain bill since I get 78-80%… I could get higher if I crushed finer, but my beer tastes great as is…I get 75% on my 3V batch sparge setup too. And now that I have a bag for my cooler, I can crush finer if I want too. Which would increase my efficiency on both 3V and single vessel BIAB.”

And another BIABer:

“I did a clone brew in my voile lined 48-qt cooler mash tun last night. I ground fine (because BIAB!) and used a published recipe from the net. OG was published as 1.063 for 5.5 gallons… I got 1.081 OG (Boil Gravity was 1.090) in 6.0 gallons… would have watered the batch down more but I only have a 7.5 gallon boil kettle! But why everyone doesn’t do it this way is kinda amazing…81.5% efficient. I still think the fine crushed grains and the voile material is the key to this. I use a $40 Corona Mill to crush, by the way and the “bag” makes up for all of the Corona Mill’s deficiencies…”

Troester writes:

“The brewhouse efficiency of the thick mashes remained almost constant between 58% and 60% over the temperature range of the experiments, but the brewhouse efficiency for the thinner mash showed a strong dependency on the temperature and was always better than the efficiency of the thick mash. That leads to the conclusion that thinner mashes perform better and allow for better extraction of the grain. Briggs also reports that thinner mashes can convert more starch but that most of the conversion potential is reached at a water to grist ratio of 2.5 l/kg” [Briggs, 2004; Braikaiser.com]¹

That thinner mashes allow better extraction is the premise for full volume mashing. In essence, the additional volume is the sparge water added to the mash tun.

2. BIAB and grinding too fine produces tannins

Simply no, as explained above. There has been reference to crushing the husks too fine which might make tannins more accessible to extraction during the mash – but not if the pH remains below 6.

3. BIAB with no sparge leaves too much sugar behind

Simply put – how can that be if efficiency is greater and predicted numbers are hit – using less grain? We know that kettle efficiency is measured relative to the conversion potential of the grain being used, and because of finer milling, if conversion is 100% of what’s available, that’s what’s in the wort. 3V brewing requires sparging – sparging dilutes. Because the WTGR ratio in a full volume mash is nearly double the ratio of 3V mash, the mash is more fluid causing the sugars to flow rather than stick – with no dilution and no change in pH.

Imagine a bag of mulch on your deck with a ½” hole cut in the bottom. You’d like to wash the sawdust off the mulch, so you get a garden hose, rip open the top of the bag and start filling the bag with water. It passes through the mulch and escapes out the hole. If the nozzle is wide open the bag fills faster than it can escape and the extra pressure from the water pushes the mulch against the hole it clogs. In brewing, that’s what’s known as a stuck sparge.

Now get another bag of mulch and dump it on your deck on top of a piece of window screen, then cover the mulch with another piece of screen and fasten one end. Get the hose and open the nozzle completely spraying all sides of the screened in mulch. The water rushes over the mulch on all sides, carries the dust with it, and exits all across the screen. In brewing, this is what happens to the sugar when using a fabric filter – and it never clogs.

4. More grain is needed to hit the numbers

With consistency, BIAB brewers report kettle efficiencies in the mid-70’s to mid-80’s, some in the 90’s. Depending on the grain bill, my personal records show 74% to 84% in every mash, but some brews have hit 89% – and not by adding more grain, in fact, by using less than the grain bill called for on a standard 3V recipe.

5. Efficiency drops when brewing big beers

This one is true … for ALL methods of brewing.

6. Squeezing the bag increases efficiency

With a fabric filter, simply squeezing the grain while in the bag adds non-diluted volume. Some BIAB brewer’s report gained efficiency if they sparge the bag and then squeeze that into the kettle – but that’s not possible unless they boil off the excess water used for sparging. This leaves the sugar behind and adds only a point or two to gravity, which may not be worth the energy cost.

Here’s why sparging a bag does not increase efficiency — the kettle wort is fixed at the same gravity as the wort absorbed by the grain in the bag. Adding water through sparging dilutes the wort moving through the grain bag and into the kettle wort – diluting it as well. Sugar stratifies as does water, so measuring the kettle gravity before stirring—and then squeezing—and then taking another reading leaves a higher concentration of sugar on the upper level of the kettle from which the sample came, which gives a higher reading. You can confirm this increase as a myth by lifting the bag, stirring, measuring, squeezing, stirring, measuring, sparging, squeezing, stirring and measuring. The last measurement will be lower than the first two, which will be the same.

7. BIAB is not “all grain” brewing

Hmmm, what do they use to make beer?

8. The bag will melt if exposed to the heating element or open flame

Not a myth, this one is for real. Your cat will melt too!

Sources:

¹ Effects of mash parameters on fermentability and efficiency in single infusion mashing.