(This article appears in the October 2002 issue of Brew Your Own magazine.  The on-line version includes an additional “step by step” section.)

The SWIG Method

Drew Avis

Imagine the slick salesman's pitch: Would you like to reduce your brewing equipment costs?  Would you like to brew two different all-grain batches of beer in the time it would usually take to brew one?  Would you like to improve your love life?  You can have all this and more, with the Split Wort of Increased Gravity (SWIG) method!

Like many long-time homebrewers, my brewing techniques and equipment have changed and evolved over the years.  My first all-grain equipment was a ZapPap lauter tun (the bucket-within-a-bucket tun popularized by Charlie Papazian in his Joy of Homebrewing), and two 20 qt stainless pots picked up cheaply from a local hardware store.  I split a full wort boil between the pots, and usually had good results. Now, after building a propane fired 3-tier converted keg system, I've moved back to the old two pots on the stove method, but with a few improvements.  I sometimes still use the 3-tier system when I want to make a lot of the same kind of beer, and when it's warm outside, but developed SWIG to diversify the kinds of beer I have on hand, and to brew through the cold winter months (of which there are many in these parts).

SWIG should appeal to a couple of types of homebrewer: small-scale (5 gallon) brewers who want to increase their volume without increasing brewing time or equipment costs, and larger-scale (10-12 gallon) brewers who find they end up with a little too much of one style of beer and would like some diversity in their brewing.


SWIG: The Theory

SWIG combines two common brewing techniques that have been practiced for decades: parti-gyle lautering, and concentrated wort boiling.  Let’s look at each technique in detail.

Parti-gyle lautering is simply the practice of drawing off a portion of the mash liquid (the first runnings) for a strong beer, adding more hot liquor, and drawing off a second, and sometimes a third, weaker running for successively lower gravity beer.  Parti-gyle lautering has probably been practiced as long as grain was mashed. In "modern" brewing, parti-gyle has a distinguished history in both English and Belgian traditions.  In 18th century Britain, brewers used the same mash to make a strong beer (XXX), a common beer (XX) and a small beer (X). The technique was abandoned for the most part with the advent of porter brewing, which used "entire" mashing (meaning the beer used the entire mash extract). In Belgium, the parti-gyle technique gave rise to the three strengths of Trappist Ale, the tripel, dubble, and single (Mosher, 1994).  

Parti-gyle presents a few challenges to the homebrewer.  The first is in recipe formulation – the gravity of parti-gyle worts are harder to predict than a standard mash, because the decrease in run-off gravity throughout the sparge is not linear.  Because the SWIG method uses parti-gyle mashing, the mash is not as efficient as some homebrewers are used to.  It is difficult to squeeze every last drop of sugar out of the mash, and total efficiencies are usually in the range of 65 to 75 percent.  A lower efficiency presents a second challenge: meeting the increased mash volume requirements because of decreased efficiency.

Concentrated wort boiling is a practice that has gained favour in modern brewing, as it permits a larger volume of beer to be produced in a brewery compared to full-wort boiling. Some breweries even ferment a high gravity wort, diluting the beer to normal gravity before packaging.  Even on the homebrewing scene, many extract brewers are familiar with this technique, boiling the malt with a limited amount of water, then cooling and diluting the concentrated wort with water before pitching the yeast.

Concentrated wort boiling has its own pitfalls, the first and foremost being the quality of the water used to dilute the boiled wort.  As one of the reasons for a full boil is sterilization, the water used must likewise be sterile.  I've found that fresh reverse-osmosis water (or "RO", a type of tightly filtered water) further treated with UV light for sterilization seems to work well, and is readily available at treated water vendors.  I try to buy dilution water the day before brewday, to ensure the water is as fresh and microbe-free as possible.

There are other challenges to concentrated wort boiling.  For example, calculating hop bitterness is different in concentrated wort as compared to a full-wort boil, because hop acids are less soluable at higher gravitys.  Also, wort darkening during the boil is more pronounced because of the higher gravity, and boil-over headspace is limited so vigilance is necessary!

SWIG: The Method

There are three key phases to the SWIG method: recipe formulation, planning, and brewing. 

As mentioned above, SWIG recipe formulation presents two challenges over standard approaches in that mash efficiency is a little more difficult to predict, and reduced hop bitterness extracted at higher wort gravities requires adjustment to the amount of hops added for bitterness and flavour.

Recipe formulation: Predicting Gravity

As with any mash method, the gravity of sweet wort collected depends on many factors which vary from brewer to brewer.  For SWIG, the challenge is to predict the gravity of two finished beers.  To start with, use Mosher's figures for parti-gyle brewing (Mosher, 1994) and then fine-tune your numbers based on your system.  Mosher suggests that in a parti-gyle mash split into two equal batches, the first runnings will take 58% of the expected extract, while the second  batch will take 42%.  This means that if a recipe should produce 10 gallons of 1.050  beer, the first five gallon batch will be a 1.058 beer, and the second a 1.042 beer.

I've found that with the SWIG method, because mash efficiency is fairly low due to the limited sweet wort collected, the numbers work out to be closer to 60% / 40% with my system, assuming a 65% mash efficiency.  For example, a mash that would produce 10 gallons of 1.056 gravity wort at a brewhouse efficiency of 65%, will produce a 1.067 and a 1.045 wort using the SWIG method.  This is for recipes with 20-24 lbs of base malt.  In theory, if you are mashing less malt, the efficiency should rise (because you are using a smaller malt/sparge ratio) and the differential between the two batches should also rise.   Of course, mash (or "brewhouse") efficiency will vary from setup to setup, and is dependant on a large number of variables, from grain crush to mash regime – but 65% is a good starting number to work from until you've done a few SWIG batches and figured out what your own setup efficiency is.

The colour from the mash seems to follow the same ratio as extract.  In other words, if your 1.056 mash has a predicted MCU of 12, the first wort will have a MCU around  14.5, while the second around 9.5.  I believe that it's important to calculated the distribution of colour as MCUs rather than SRM, because the former is linear.  Once calculated, you can then convert the number to SRM to check style conformance.

Calculating colour

Malt colour is measured in degrees Lovibond, and with the Lovibond numbers you can calculate Malt Colour Units (MCUs).  Simply multiply the weight of each malt by its Lovibond, add the products, and divide by the final beer volume in gallons.  For example, if a 5 gallon recipe consists of 8 lbs 2-row (1.8 Lov), 1 lb crystal 40 (40 Lov), and 4 oz chocolate malt (300 Lov), the MCUs are: ((8x 1.8) + (1 * 40) + (.25 * 300)) / 5, or (14.4 + 40 + 75)/5, or 26.

To convert MCUs to an estimated SRM, use Dan Morey's formula: SRM = 1.4922 [(MCU) ^ 0.6859] - for values of SRM < 50

In the above example, the estimated SRM is 14.


One advantage of SWIG brewing is that you can add specialty malts to the second mash session, creating an entirely different second wort.  This means you can brew a stronger, pale beer and a second weaker dark beer, two pale beers of different gravities, or two dark beers of different gravities.  By adding sugar or malt extract to the kettle, you can brew two beers of similar strength.  Here are some ideas for successive beers using SWIG:

First Beer


Second Beer


Specialty Malts

Helles bock


Brown Ale


med crystal and chocolate


1.080 (add candi sugar to the boil)








caramel malt, honey malt, chocolate

Pale Ale


Cream Ale


light crystal

Old Ale




dark crystal, chocolate


The second addition of specialty malts will add colour, flavour, body, and possibly a few points of extract.  Very little is required to add colour and flavour – typically .5 to 1.5 lbs will suffice.

Recipe formulation: Hop Bitterness

There are several different methods of calculating hop bitterness, and at least two of them (Garetz & Tinseth, as detailed in Norm Pyle's Hop FAQ) account for wort gravity.  At higher gravities, alpha acids are less soluable, meaning less bitterness is extracted from the hops.  Comparing Tinseth calculations for a normal 1.059 SG boil to SWIG 1.059 batch (a 1.084 boil diluted to 1.059 with water) suggests that utilization is about 30% lower for the higher gravity boil.  This means that you need to add about 30% more bittering hops for recipes adapted to SWIG brewing.

Planning: What's different?

SWIG brewing requires a little more forethought as managing two simultaneous boils is challenging.  My planning is aimed at saving time, and making two-boil management as easy as possible.  Here are some planning and preparation ideas to make a SWIG session easier:

Several steps are concurrent, meaning (for example, if there is a 30 minute lag between worts):

It is useful to track the times on each pot to ensure you add hops, irish moss, etc at the right times for each brew.


Brewing: A Step By Step Tour

Here's a step by step account of a recent SWIG brew session, to give you the flavour of this technique.

To prepare for the Christmas season, I decided to brew a helles bock and a Northern brown ale.

Step 1 – recipe formulation

First, I knew from previous batches I'd need about 22 or 23 lbs of base malt to hit the target gravity for the helles bock.  Crunching the numbers showed that my grain bill of:

would yield 10 gallons of 1.056 wort, given 65% brewhouse efficiency.  With the 60/40 split of gravity, the first 5 gallon batch would be 1.067, perfect for a helles bock, and the the second would be 1.045, perfect for a Northern Brown ale.

Calculating SWIG Gravity

How did I figure out the grain bill for the helles/brown would yield two worts of 1.067 and 1.045? 

First, calculate the total possible gravity points the malt bill could yield in 10 gallons of beer.  This is the weight of each malt x potential points / beer volume.  For the malt bill:

(18 x 38) + (2 x 33) + (1 x 33) + (2 x 39)

or 861 points / 10 gallons

= 86 points, or an OG of 1.086

Second, calculate the extract given a 65% brewhouse efficiency:

86 x .65 = 56 points, or an OG of 1.056

Finally, the 60/40 split is calculated as:

2 x points x .6 (first wort) and 2 x points x .4 (second wort).

2 x 56 x .6 = 67 points, or an OG of 1.067 

All of these calculations are the reason I use homebrew recipe calculation software!


The brown ale would require some specialty malts to get the right colour and malt profile.  I decided on:

Giving me 21 MCUs in 10 gallons, or 12 degrees SRM, making the beer about 16.5 SRM, right in the range of 15 to 22 that the BJCP says this style should be.

Finally, the hopping schedule was fairly simple, to make it easy to keep track of what needed to be added when:

To Helles and Bock Maibock:

Finnigan's True North Brown:

At a normal gravity, these hop schedules would yield 20 IBU (bock) and 27 IBU (brown).  At the concentrated wort boil gravity, I needed to increase the bittering hops (Galena in both cases) by 30% (or to .65 oz) to compensate.

[Note – from here to sparge is optional, as it's pretty much the same as with any all-grain batch]

Step 2 – Prepare the strikewater

Mashing 23 lbs of grain in a  10 gal mashtun requires a fairly thick mash (of course, if you have a larger mashtun, you can use a thinner mash). At 1 qt/lb, this means 23 qts of water.  According to my brewing software, I should strike at 172F to hit my first rest temp of 152F.  Of course, with two 20 qt pots, this means splitting the strike water between the pots.  I use a 50/50 RO water / tap water mix because my tap water is quite hard.

Step 3 - Mash-in

A thick mash requires careful attention to ensuring that the grain and water are well-mixed to prevent balling (little balls of dry malt that never get converted).  I add ½ the strike water, carefully add malt a qt at a time, stirring between each qt to ensure a consistent mash.  I then add the second half of the water followed by the malt in the same manner.

Sacchrification  rest 

Using good 2-row, a single-infusion mash should convert fully in 45-90 minutes, depending on the rest temperature, and malt type.  I usually test for conversion after 60 minutes, and then again every 10 minutes thereafter until the iodine test indicates there's no more starch in solution.  (For an iodine test, place a teaspoon of mash liquid on a white plate, and add a drop of plain drug store iodine.  If it turns black, there is still starch in the mash; if it remains rusty red, the starch has been completed). This session took a full 90 minutes to convert, probably because I was using fully-modified British two row, and a lower saccrification temperature.

Step 4 - First Sparge

You can use either a fly sparge or batch sparge technique with SWIG, either will produce acceptable results.  In a fly sparge, water is continually sprinkled on the top of the grain bed while sweet wort is collected, and typically a depth of one or two inches of water is maintained above the grain bed.  In a batch sparge, the tun is drained completely, then a second charge of sparge water is added to the mash, which is drained again.  Batch sparging is faster, but may affect efficiency between the two batches somewhat.  I use a fly sparge, slowly adding sparge water to the mash tun from the second pot as wort is collected in the first.  I like to keep my sparge water temperature around 170F, which means the mash slowly heats up from the high 150s to the high 160s as the sparge progresses.


Step 5 - First boil

Set the first pot on the stove and start it boiling.  On my stove, I need to cover the pot until the wort looks like it's just about to boil (usually takes 20 minutes at the highest setting).  If I don't cover the pot, it takes over an hour to boil.  If I don't watch the pot and take the lid off at the right time, it's a guaranteed boil-over!  Vigilance is key.

I use a good kitchen timer to keep track of the time for hop additions, and an Irish moss addition at 20 minutes.


Step 6 - Second Sparge

While the first pot comes to a boil, it's time to sparge the second wort.  I add the specialty malts to the top of the mash and give them a stir to incorporate them into the top layer.  I then add the second sparge water (all the water from the second pot – which I now need to collect wort!), and recirculate until the runnings are clear (it takes less recirculation the second time). 

I then collect another 18 qts of wort in the second pot, and put it on to boil, approximately 20 minutes behind the first pot.


Step 7 - Hopping

It really helps to plan your hopping ahead of time with a chart based on when the first pot comes to a boil.  Both of these beers were first wort hopped, because I like the enhanced aroma FWH lends to a beer, and because of the convenience. 


Step 8 - Chilling

The first batch is chilled while the second is still boiling.  The reduced boil volume means reduced chilling times, and I find I can get the pot down to ~80F in about 15 minutes.  If you're able to chill your topping up water, you can reduce the wort temperature further when you dilute – I keep my topping up water on the back porch if it's cool outside for this extra chilling effect.  For the brewer without a chiller, the SWIG method presents the possibility of cooling the wort by placing the pot in a large tub of ice water. 

Once the first pot is cooled, I whirlpool the hops and trub, let everything settle, then start to run the chilled wort to the fermentor, rehydrate the yeast (if I'm using dry yeast), and start chilling the second pot.

With a concentrated wort, every drop of wort left in the kettle is a significant loss of final beer.  As the wort is siphoning from the kettle to the fermentor, I "rinse" the hops with some topping up water to extract more wort from them.  I simply add a few quarts of water to the pot when the wort level is getting low.

Step 9 - Topping up

Topping up the transferred wort is the last step before pitching the yeast.  I sterilize the lip of the water container, and pour in enough pure water to bring the total volume up to 20 litres / 5 gallons.  At this point I use a wine thief to take a gravity reading, after agitating the fermentor enough to completely mix the wort and water.

While the first fermentor is being topped up, I start transferring cooled wort from the second pot to the second fermentor.

Step 10 - Pitching & Fermenting

This step is no different from any other method of brewing, except you now have two fermentors to watch and care for.  With a lager/ale split batch such as this one, it's useful to have a warmer area of the house for the ale, and a cooler area (such as a lagering fridge) for the lager.  And if you've brewed two similar looking beers, it's a good idea to mark the carboys to indicate which is which – it could avoid some confusion!


Final Thoughts

SWIG is a technique I have developed to be able to move back indoors and brew more kinds of beer with less effort, and I've discovered it produces very good beer – as good as the beer I was making with full-wort boils.  The advantages to SWIG are many: decreased energy and chilling water usage, decreased equipment costs, the ability to brew indoors, avoiding over-sparging, and the ability to produce two different beers from the same mash in the time most brewers take to make one – these are just the most obvious advantages.  There are many permutations brewers could make with this technique, limited only by imagination and the number of burners on your stove and stock pots in your cupboard.  For the brewer already doing full-wort boils on the stove, it would be a simple adjustment to collect a concentrated wort then a regular wort – all you need is an additional 20 qt pot.  SWIG can also be used to brew smaller batches of stronger beer (such as dopplebocks, barleywines, and imperial stouts).  And for the beginning all-grainer who wants to limit complexity, a single pot and 15 lbs of mash could be employed for a single concentrated wort session with good results.


References and notes


Mosher, Randy.  Parti-Gyle Brewing.  Brewing Techniques, March/April 1994.


Mosher suggests that for any mash designed to gravity, 58% of the points will be in the first half, 42% in the second half. 

Pyle, Norm.  Hops FAQ.  Internet: http://www.realbeer.com/hops/FAQ.htm.


Drew Avis lives and brews in the tiny village of Merrickville, Ontario.  He is the author of StrangeBrew homebrewing software, and a member of the Members of Barleyment.  His homepage is at strangebrew.ca.