The Electric Brew in a Bag Build

Electric Brewing

Electric brewing has been around for some time and its advantages are well known to the brewing community. They include the ability to brew inside all year long, use of a readily available and cheap energy source (as compared to propane) and greater energy efficiency.

As an example, a large home brewing heating element dissipates 5500W. For a 5 gallon batch, it can be estimated to run at 100% for about 30 minutes and at reduced power levels during mash and boil. Averaging this to a 2 hour use at 100% power, the cost of an electric brew day for a 5 gallon batch comes to about $1.50 in energy cost. With the heating element immersed directly in the wort, heat transfer is as efficient as it can be. Temperature control is also more precise than in gas setups. And no more trips to the gas station to get refill the tank that ran out in the middle of your boil…

Brew in a Bag

Brew in a bag (BIAB) is a great single vessel all grain brewing method which can produce excellent beer while being far more space efficient and wallet friendly that your traditional RIMS/HERMS multi vessel setups. There is a ton of material out there on the basics of brew in a bag. Ben Cull from Mash Hacks has a great video entitled “The Simplest All grain brew day”. It’s is well worth the watch if you’re thinking about getting into all grain brewing

There is similarly a great bit of misinformation about biab being a “lesser” form of brewing. It is sometimes claimed to have reduced mash efficiency and generally less repeatable brewing. There’s enough literature out there addressing these myths (see also this great sticky thread by Bobby from and single vessel bag brewing has gained popularity with home brewers because of its numerous advantages:

  • Less equipment, which leads to:
  • Lower cost
  • Less space needed
  • Less cleanup
  • Faster brew days
  • Simpler process, less screwups: no stuck sparges, no need to mash out, etc…

Electric brewing in bag has grown popular in the past years, and vendors offer some impressive turnkey systems. These include SS brewtech, Clawhammer, Brew-Boss, High Gravity, and many others. The cheapest turn key solutions out there seem to be $800-$1000 and are typically 120V/15A setups. The 240V/30A setups are closer to the $1500 price point.

The DIY Approach

I set out with a goal to build a full electric brew in a bag system for around $500. I wanted to build a system for myself that could beat those kinds of prices and be a fun project at the same time. This blog documents this process.

The final price tag of my setup was closer to $650.  I did not quite meet the budget, but I did make the decision to splurge on a few items.  As I catalog this process, I will also suggest cheaper alternatives that will achieve the same functionality and will bring the final price tag closer to $500.

My setup and “brewery”

I will cover the build in a few separate posts, roughly following this outline:

Enjoy the reading, leave me a comment, and perhaps this will inspire you to look into building your own budget setup!

Let’s get to it!

Conversion Efficiency: You’re doing it wrong.

Conversion efficiency is a measure of how much of the available sugars and dextrin are extracted from the grain by the mashing process. It is a simple metric as it is independent of any brew house parameters. The only variables that matter are the weight of the grain, the weighted average potential, the amount of water used and the gravity measurement.

Conversion efficiency is simply the ratio of of measured gravity points per pounds per gallon (ppg), or degrees Plato, to maximum possible ppg (or degrees Plato). The question then is how do we calculate the maximum possible ppg a grain bill can yield.

Grain Potential

In “How to Brew”, while describing grain potential, John Palmer states:

One pound of sugar will yield a specific gravity of 1.046 when dissolved in 1 gallon of water.

John Palmer, How To Brew

This, it turns out, is incorrect and has been the source of many a headache. I know, I know, who am I to correct Palmer?? Take a look at this long thread where the intricacies behind the above statement are unpacked.

The correct definition is rather that one pound of sugar will produce 1 gallon of wort with specific gravity of 1.046. A gallon of wort is not equal to a gallon of water, because the dissolved sugar occupy a certain volume. In other words, if we dissolve 1 lbs of sugar in 1 gallon of water, we will not measure a specific gravity of 1.046. If we dissolve 1 lbs of sugar in whatever amount of water will yield 1 gallon of wort, we will indeed measure a specific gravity of 1.046.

Doing the Math

One can demonstrate this mathematically. Degrees Plato are used to quantify the concentration of sugar in water as a weight percentage.

\[^o P = 100 \times {sugar_{weight}\over (sugar_{weight} + water_{weight})}\]

1 gallon of water weighs 8.3304 lbs, and thus the gravity of 1 lbs of sugar dissolved in 1 gallon of water is

\[100 \times {1\over (1 + 8.3304)} = 10.71^o P\]

Using just about any table or online calculator, the SG equivalent of 10.71 deg Plato is 1.043, not 1.046.

We can approximate how much water we need to produce a gallon of wort by using the density of sugar, which is 1.59 g/cm^3 or 13.16 lbs/gallon. One pound of sugar should thus occupy a volume of 1/13.16=0.076 gallons. Therefore the amount of water needed would be 1-0.076=0.924 gallons.

Using about 0.924 gallons of water will yield a gallon of wort with gravity given by

\[100 \times {1\over 1 + (8.3304*0.924)} = 11.50^o P\]

This corresponds to an SG of 1.0463. Thus the potential of sugar of approximately 46 gravity pts/lbs/gallon is necessarily defined as per gallon of wort and not per gallon of water.


Let's do a kitchen counter experiment to demonstrate this. Scaling things down, let's dissolve 4oz of sugar in 1qt of water and compare it to dissolving 4oz of sugar in 0.926 quarts of water. Measuring everything by weight, the relevant values are captured in the following table.

1 qart water1 quart of wort
water vol (gallons)0.2500.231
water weight (lbs)2.083 (945g)1.928 (875g)
sugar weight (lbs)0.250 (113g)0.250 (113g)
wort weight (lbs)2.333 (1058g)2.178 (988g)
wort vol0.2680.250

because my scale has better display precision in grams, I converted everything to grams.

Small measurement and instrument errors not whistanding, we can see that 1 quart of solution is closer to the target 1.046 specific gravity than 1 quart of water, confirming the math shown above.

So what... ?

This may not seem important, but if you are, like me, the kind of brewer that likes to understand and hit targets on brew day, then it is less trivial than it seems. Popular efficiency calculator online make this mistake. For example, here is a screenshot from Brewer's Friend efficiency calculator.

Brewer's Friend Efficiency calculator

While the form does say "Wort Volume", the description given is "How much water was used. This is a reasonable request, given that brewers will know the volume of water they used, but not the volume of wort was produced. And so the answer is wrong. The calculator should have used the plato formula and calculated the weight of water and given an answer of 1.043.

When entering a grain bill and expecting an efficiency from the calculator, the resulting efficiency will be substantially undershot.

Let's run some more interesting numbers. Say we dissolve 12 lbs of pilsner malt with an 80% potential into 8 gallons of water. The plato formula will return the following gravity.

\[100 \times {(12 \times 0.8)\over (12 \times 0.8 + 8 \times 8.3304)} = 12.59^o P\]

This corresponds 1.051 SG. What does the online calculator yield?

12 lbs of grain in 8 gallons of water

We are told our conversion efficiency if under 92%, when in reality it is 100%. 8% is a significant error and it will impact the ending brewer's efficiency and thus recipe design, OG, FG, ABV etc...

Note that if we account for the added sugar volume, the calculator is correct. Once again we multiply the sugar weight with the density of sugar to get the added volume

\[{{12 lbs \times 0.8} \over 13.16 gal/lsb} = 0.73 gallons\]

Using 8.73 gallons in the calculator, we get the expected 100% conversion efficiency. We can be fairly certain that the wort vs water is the mistake made by the calculator

Grain Moisture

We kept the above simple, but there are other variables in play, that puts Brewer's friend calculator even further from an accurate result. Grain is not 100% dry and grain spec sheets will typically quote a grain moisture content of around 4%. This means that 4% of the grain is water. It once again may not look significant, but the small number is deceptive.

Compounded by the water volume mistake described above, the end result is severely lower than expected.

If 4% of the grain is water, then only 96% of it contributes to sugar extraction and the maximum possible gravity is:

\[100 \times {(12 \times 0.96 \times 0.8)\over (12 \times 0.96 \times 0.8 + 8 \times 8.3304)} = 12.15^o P\]

This corresponds to a gravity of 1.049. Let's pause and think about what this means for the brewer entering numbers into an online calculator. He may have worked very hard to get a great mash going and extracted every last bit of sugar available, only to be told that his conversion efficiency was 88%!

Again, if we fake out the calculator by entering the correct wort volume AND the weight of the dry grain, we get the correct results:

Note that we could also add the water content of the grain to the mash water, although that is a negligible amount and the resulting gravity would not have changed within the precision we are using here.


Conversion efficiency is simply the measure of how much extract a mash yields, compared to the maximum that can be extracted. As such it is an important concept as it directly relates to the quality of the mash. Braukaiser has a great article on efficiency where the various things that influence a good conversion are described in detail. It's worth a read (and re-read).