ezBIAB Calculator©

Brew In A Bag Brewing   The first time I brewed using my brew in a bag system I wondered how much grain and brewing water would fit inside my kettle without causing it to overflow? Then I wondered how much wort would be left in the kettle after removing the grain bag? Before switching from a traditional three tier system to BIAB these calculations had never been too much of a problem. Having a separate hot liquor tank, mash tun and brew kettle made calculating mash thickness and preboil volumes pretty straightforward.

Soon after I decided to sit down and write a BIAB calculator of my own for a number of reasons. I saw it as a great way to become more familiar with the variables associated with BIAB brewing. I also needed a way to reliably calculate BIAB volumes and gallons, based on the pounds of grain used in my recipes, all at the same time. The very first brewday after using ezBIAB Calculator© I was able to hit all of my BIAB volumes right on target. After calculating how many pounds of grain the recipe would use to reach the gravity I had in mind ezBIAB Calculator© had crunched the numbers for my Hiphopapocalypse IPA® recipe perfectly. 

ezBIAB Calculator©
With BIAB brewing all of the water and grain used in the mash goes into the kettle at the same time. During the mash grain is put inside a fine mesh bag so that sugars can be extracted into the wort without any of the grain getting into the kettle. At the end of the mash the grain and bag are then removed and the wort remaining in the kettle is brought to a boil. The trick in all of this is in not causing the kettle to overflow with too much mash volume during the mash while being able to hit your preboil wort volume after the grain has been removed.

Getting the mash volume to fit inside the kettle without it overflowing and hitting your preboil volume at the same time is like trying to juggle while riding on a see saw. You have to balance the amount of grain and water used in the mash, the mash thickness, the amount of water the grain will absorb and the size of the kettle being used. You also have to make allowances for the wort absorbed by hops, wort left behind in the kettle as cold break and the evaporation of water from the wort during the boil. Those calculations along with wort loss to lines, chillers and tubing are critical in determining your preboil wort volume.  

"In a perfect world the brewer's kettle is always large enough to hold all of the water and grain needed for any recipe. Then after the grain has been removed the wort in the kettle is always perfectly equal to the recipe's pre-boil volume. And at the end of the boil there's always enough cooled wort to fill the fermentor right up to the line. Of course once the fermentation has completed there is enough tasty beer to be packaged into kegs, bottles or cans."

In reality in order to reach your pre-boil volume some make up water has to be added to the kettle once the grain bag has been removed. This happens when the kettle is undersized and unable to hold all of the water and grain required for the mash and boil at the same time. Or if a brewer decides to leave room in the kettle and then reach their pre-boil volume by rinsing the grain with additional hot water. Sparging the grain is useful when brewing high gravity beers requiring a larger percentage of grain. It also results in a thicker mash because there is a lower percentage of water in the kettle during the mash.

Calculating Fermentor Volumes

If the goal is to package 5.00 gallons of beer the fermentor will need to be filled with 5.25 gallons of wort, in order to make up for 0.25 gallons of fermentation trub loss. Fermentor trub loss is made up of yeast, proteins and hop debris that eventually settle out into a compact layer at the bottom of the fermentor. It's the kind of stuff you don't want ending up in your finished beer. The amount of fermentor trub loss will vary with the strain and amount of yeast pitched and the percentage of trub initially transferred to the fermentor from the kettle.

Calculating Kettle Volumes

Kettle trub is made up of break material and proteins formed during the boil that under most conditions will remain in the kettle and not be transferred to the fermentor. In order to have 5.25 gallons of wort to fill the fermentor at the end of the boil the post boil wort volume has to be calculated accurately. If the kettle boils off 1.25 gallons of wort per hour, during a one hour boil, and the kettle trub loss is 0.75 gallons then 2.00 gallons of wort is the total kettle loss. NOTE: Hops will also absorb a small amount of wort during the boil depending on the weight of hops added to the kettle.

By adding the 2.00 gallons of kettle wort loss to the 5.25 gallons of wort needed to go into the fermentor we come up with a pre-boil volume of 7.25 gallons. We prove that by subtracting from the 7.25 gallons of wort pre-boil volume 0.75 gallon for kettle trub loss and 1.25 gallons for boil loss leaving 5.25 gallons of wort left for transferring into the fermentor. After fermentation 0.25 gallon of trub will remain in the fermentor leaving 5.00 gallons of clean beer just waiting to be packaged.

Calculating Mash Volumes

To end up with 7.25 gallons of post boil wort in the kettle, after the grain bag has been removed, several other variables also need to be factored in. With BIAB brewing the entire grain bill is mixed together with brewing water inside the same kettle that will also be used as a mash tun. The ratio of brewing water to grain is used to determine the thickness of the mash which is then used to determine the amount of room the mash will take up in the kettle. Its the sum of the mash volume added to the preboil wort volume that determines what size kettle will be needed to keep the wort from overflowing. When using a kettle that's been right sized for the volume and gravity of the beer your brewing the mash will be thinner than that used in a three tier system.

Figuring out the best kettle size for brewing gravity of beer you brew the most often is very important when brewing BIAB. I always recommend using the largest sized kettle that's practical for your your budget and brewing needs. Getting the wort pre-boil volume correct on brewday is a major milestone in the BIAB brewing process. Using a smaller kettle means you'll be sparging the grain in order to make up for the loss in preboil volume. It also means that your mash will be thicker and depending on how much thicker it will produce a less fermentable mash than a thinner mash would. As you progress in your BIAB brewing you may also want to factor in things like wort loss due to shrinkage as the wort cools down in the kettle or losses in hoses and chillers.  

ezBIAB Calculator©

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A Little Mashing Theory Goes A Long Way

As a self proclaimed single infusion mash fly sparger brewing on a traditional three tier brewing system, my goal was to always get my mash thickness as close to 1.25 quarts of water per pound of grain. Mash thickness plays a key role in the brewing process when it comes to getting consistent results in your finished beer. With BIAB brewing all of the water volume is mixed with the grain and added to the kettle for mashing at the same time. This creates a much thinner mash than the 1:25 quarts of water per pound of grain used in a traditional mash.

BIAB Conversion And Efficiency

The mash thickness associated with BIAB brewing is much thinner than that used in a three tier system. Due to the higher ratio of water to grain the concentration of converted sugars will be lower, which in turn produces a more fermentable wort. The same higher ratio of water to grain lowers the concentration of enzymes in the wort slowing the breakdown of proteins.

Extended mash times help compensate for the slower conversion rate of a thinner mash and using a mash efficiency of 70% is a good starting point. As with any new brewing system a couple of brewdays are required in order to get your process and efficiencies dialed in more accurately.


Traditional Conversion And Efficiency

The thicker 1.25 quarts of water per pound of grain mash thickness, used in traditional brewing, produces a wort that has a higher concentration of enzymes. The higher concentration of enzymes breakdown proteins more efficiently converting starch into sugars faster. Since the ratio of water to grain is lower the concentration of converted sugars will be higher producing a less fermentable wort and a maltier sweeter beer.


Maximum Kettle Volume: The maximum amount of grain and water that the kettle can safely hold before a spill over is likely to occur. Sometimes referred to as the actual working volume of the kettle. Depending on the size of the kettle this can be many gallons less than the kettle's actual gallon rating. In the example below the 62 quart kettle used in my BIAB RIMS setup has a lip located one inch down from the top of the kettle. The top of the grain basket rests on that lip to keep the basket from touching the heating element located at the bottom of the kettle.

A 15.5 Gallon Kettle Safely Holds Just 13 Gallons

In addition to that there is also a spray nozzle mounted in the kettle lid that sprays temperature controlled wort evenly over the grain bed. Keeping a two inch distance between the tip of the nozzle and the top of the wort  maximizes the spray coverage over the largest area of the grain bed. When setting up my ezBIAB calculations I enter 13 gallons for the maximum kettle volume instead of the 15.5 gallon kettle size.


Packaged Beer Volume: This is the total volume of beer that you planned to package into cans, bottles or kegs. When your beer comes out of the fermentor for packaging a layer of yeast, or fermentation trub, will be left behind in the fermentor.

Plan Ahead And Have Enough Fermented Beer To Package

If a fermentor was initially filled with 5 gallons of beer at the end of fermentation a little bit of beer may be lost during fermentation through the airlock or blow off tube too. To allow for beer lost during fermentation, and ensure you end up with enough beer to fulfill you packaging needs, enter the volume of beer expected to be lost during fermentation.


Kettle Trub Loss: This value has more importance for brewers who believe that only wort should ever go into their fermentors. If that is the case then a certain amount of wort and kettle trub will always be left behind in the kettle after filling the fermentor. In my kettle that can amount to as much as three quarts for some recipes that include plenty of hop additions.

Kettle Trub Loss Will Vary With Kettle Size And Brewing Process

For some brewers transferring the kettle trub along with the wort into the fermentor isn't a big deal. I can't imagine kettle trub being magically transformed into drinkable beer during fermentation, and that's where fermentor trub loss will come into play. If you plan to add all of the kettle trub into your fermentor then enter zero as the kettle trub loss, but be sure to include that amount and more in your fermentor trub loss calculation.

If you choose to keep the kettle trub out of your fermentor then add that amount of wort lost to your kettle trub loss calculation. Eliminating kettle trub from going into your fermentor will then allow you to enter a smaller amount of trub loss in the fermentor trub loss calculation. As an example the post boil volume will need to be larger to compensate for the wort and trub left behind in the kettle.


Weight of Grains: This is the total amount grain used in the recipe, here you simply enter the weight of the grains in pounds. The grain weight is used in calculations that determine the grist to water ratio when they are mixed together in the mash tun, also referred to as the thickness of the mash, or the mash thickness. When grain is mixed with water a percentage of that water will be absorbed by the grain, the amount of water absorbed by the grain is referred to as grain absorption.

Weight Of Grains Used In A Recipe

An acceptable method of calculating the percentage of recipe water lost to grain absorption can be expressed simply as the weight of grain times 0.125 equals water lost in gallons. There are some variables outside of this formula that can change the actual amount of water loss although not by much. Squeezing the grains, and the method of squeezing the grains, will extract more wort from the grain and lower the amount of water needed to compensate for the amount of water absorbed by the grain.


Weight of Hops: The total weight of hops used in the recipe, here you simply enter the weight of the hops in ounces. The hop weight, is used in calculations that estimate the amount of water needed, to compensate for wort that will be absorbed by the hops as they sit in the kettle. There are other variables that affect the amount of water lost to hop absorption too. The amount of hops used in the recipe and the type of hops whether flower, whole leaf or pellet will all influence the actual amount of extra water that will be needed.

Weight Of Hops Used In A Recipe

An acceptable method of calculating the percentage of recipe water lost to hop absorption can be expressed simply as the weight of hops times .0.0365 equals water lost in gallons. Here again variables in how the brewer chooses to remove the hops from their wort will affect the amount of water absorption. If hops are added directly to the kettle they eventually end up settling on the bottom of the kettle as trub. If hops are bagged before they're added to the kettle some brewers may opt to squeeze the hops and collect the extra wort in the kettle.


Fermentor Trub Loss: At the end of a successful fermentation yeast cells having run out of maltose to eat, eventually fall out of suspension and settle on the bottom of the fermentation vessel. This layer of debris is referred to as fermentor trub and its made up mostly of heavy fats, proteins and inactive yeast.

Trub Loss Produced During Fermentation

As an example, on bottling day you have 0.5 gallon of trub at the bottom of your fermentor and you want to package 5 gallons of beer. Enter 0.5 as the fermentor trub loss, to compensate for the 0.5 gallon of volume the trub will take up. You would then need to transfer 5.5 gallons of wort from the kettle to the fermentor to have enough fermented beer needed to package 5 gallons.


Length Of Boil: This is the length of time the wort will be boiled, here you simply enter the length of the wort boil in minutes. The length of the wort boil will vary between recipes, as a way to adjust bittering, or the isomerization of alpha acids of hop additions. The boil also creates the maillard reaction in the wort that darkens and adds flavors of toast and caramel that couldn't be added in any other way. Brewers may also vary the intensity of the boil, how vigorous the boil is, by controlling the amount of heat applied to the kettle.

The boil also halts enzyme activity in the wort to prevent any further conversion of dextrin into fermentable sugars. The heat and turbulence of the boil sanitizes the wort and promotes the formation of hot break which is made up of proteins and tannins, the foam and brown scum that collects on top of the wort. Many brewers add a fining agent to the boiling wort to help the break material coagulate and fall to the bottom of the kettle, or use whirl pooling as a way to clear their wort of  break material.

Evaporation Rate Of Wort During The Boil Depends On Several Things

Boil Off Rate: This is the volume of the wort that will be lost to evaporation as the wort is boiled. Simply enter the estimated amount of wort boiled off in gallons per hour. The wort volume in the kettle will be reduced at a rate depending on the shape and size of the kettle, the length of the boil and how vigorous the boil is. Referred to as the boil off rate this value may take you a few batches, in order to get the closest average boil off rate for your brewing system.