Parti-Gyle Brewing – Two Beers from One Mash

by Brad Smith on October 7, 2011 · 18 comments

Parti-Gyle brewing is a method for making more than one batch of beer from a single all grain mash. It offers tremendous flexibility since you can brew two beers of different gravities, and also add different hops and yeast to create distinct beers from one brewing session.


Parti-Gyle brewing is not a new method. The method goes back hundreds of years, and many modern sub-styles are examples of light and heavy versions made from a single mash. Examples include the various weights of English and Scotch Ale, various grades of Bock, and even variations of Trappist ales. In the 1700’s and 1800’s it was very common to create a strong beer from the first runnings of the mash and a lighter common beer from the second runnings of a mash.

The Parti-Gyle Method

The standard method for Parti-Gyle brewing is to make two beers from a single mash. Typically a fairly high gravity beer is made from the “first runnings” of the mash, and the second runnings are boiled separately to make a lighter beer. Often different hop additions, boil additions and yeast are used to create distinct styles from the two runnings depending on the brewer’s preference.

Estimating the Gravity of Each Beer

When designing a parti-gyle beer, one is usually concerned with gravity and color of the two beers being created. This is important for determining how much grain is required for each beer and also how much liquid to run through each to achieve a target boil gravity. The rule of thumb for an average mash is that 2/3 of the gravity potential is in the first 1/2 of the runnings. This is due to the fact that most of the high gravity wort comes in the first third of the lauter.

One common parti-gyle split is 1/3 volume for the first runnings and 2/3 volume for the second which results in a first batch of beer that has twice the points that the second batch will have. So for example if the total mash had an estimated original gravity of 1.060, we would expect the first 1/3 to have a gravity of 1.090 and the second to have a gravity of half the points or 1.045.

For a 50-50 split by volume, with half of the wort in each batch we get a roughly 58% of the gravity points in the first batch. So a 1.060 overall batch OG would translate to a 1.070 first runnings and 1.050 second runnings, with both of equal size.

Estimating OG for Split Batches

To perform these calculations yourself, start with the OG estimate of the mash runnings using conventional methods. This can be done using the method described here, except you use the mash efficiency and total lauter volume instead of the overall brewhouse efficiency and overall batch volume to get your mash OG estimate.

Once you have the OG estimate for the overall batch, get the number of points by subtracting one and multiplying by 1000, so 1.060 becomes 60 points. Next we use the following to calculate the final number of points in this fraction:

Number_points_ runnings = (Tot_points * Points_fraction / fractional_volume)

So if we look at a 1.060 total gravity estimate with a 1/3-2/3 volume split which has half the points in each runnings we get 60 points, 0.5 as the points_fraction and 1/3 or 0.333 as the fractional volume:

Number_points_runnings = (60 * 0.50 / 0.333) = 90 points or a gravity of 1.090

The second runnings of 2/3 is:

Number_points_runnings2 = (60*0.50 / 0.666) = 45 points or 1.045 gravity

Using the same equation, you can come up with an accurate estimate for the gravity of each of the runnings based on the original gravity of the overall batch.

Color Considerations

It should be no surprise that the color of the two batches in a parti-gyle will be darker for the first runnings and lighter for the second in most cases. Calculating the actual color for a regular beer is described here, and is based on the Malt Color Units (MCUs) which are simply the sum of the pounds of malt times their color for all grains in a batch.

Looking at the examples above – a 50-50 volume split has about 2/3 of the gravity in the first runnings and 1/3 in the second runnings. The malt color units follow, so about 2/3 of the MCUs will be in the first running and 1/3 in the second. So if you calculate the overall Malt Color Units for the total batch (sum of the pounds of malt times color of each malt), you can multiply it by 2/3 or 1/3 for each running and then apply the Morey equation to get the color estimate for each of the runnings. Here the OG_FRACTION refers to the 2/3-1/3 OG split so you would apply 2/3 to the first runnings and 1/3 to the second:

SRM_color = 1.4922 * ((MCU * OG_FRACTION) ** 0.6859)

Since the Morey equation is not linear, you will see a larger color difference for a parti-gyle beer when working with lighter beers. So for a very light beer and a 50-50 volume split, the first runnings will be almost twice as dark as the second runnings. However as the beer gets darker the difference will be smaller – to the point where the second runnings of a Stout beer might have no perceivable difference in color from the first.

After the Mash

Once you have mashed your parti-gyle beer and taken the two runnings, the rest of the brewing process is the same as with any other beer. Obviously the two runnings are boiled separately so you either need two boil pots and heat sources or a sterile way to store one of the runnings for a few hours while you boil the other.

One of the great features of part-gyle brewing is the ability to change the character of the beer in the boil and fermentation. By adding different hop additions, yeast, spices or steeping additional grains prior to the boil (much like an extract brew) you can dramatically change the character of the two beers produced. With a little imagination you really can create two distinctly different beer styles from a single brewing session.

For design purposes it is usually best to treat the two runnings as separate beers at this point, and the usual rules for estimating bitterness, final gravity and fermentation apply. The design possibilities are nearly endless. You could create a strong ale and bitter, a wheat bock and weizen, a brown and pale and many other combinations from a single mash.

I hope you enjoyed this week’s article and decide to make your own parti-gyle brew in the future. Thanks for dropping by, and please subscribe to my blog or podcast for more great articles and sessions on brewing beer.

Related Beer Brewing Articles from BeerSmith:

Enjoy this Article? You'll Love Our BeerSmith Software!
  Don't make another bad batch of beer! Give BeerSmith a try - you'll brew your best beer ever.
Download a free 21 day trial of BeerSmith now

{ 13 comments… read them below or add one }

Paul Young October 7, 2011 at 4:34 pm

Hmm, this could be a lot of fun! It got some wheels turning. I have split 10 gallons batches before for example a stout into one regular and one vanilla but never tried to get two different styles from one mash.

Lucas E Szymanowski October 7, 2011 at 5:29 pm


Now how about a sample recipe….

Fred October 12, 2011 at 6:01 am

I tried this method last year and ended up combining the different batches to create a fantastic Rye IPA. I’m working with my HBC to do a series of these and will enter into a competition next year.

Great Article, thank you!

Jim October 17, 2011 at 1:46 pm

Talk about resourcefulness. That will pay off in a big way in a few weeks when you have a choice of which beer to crack! I’m sure both will be splendid.

michael kelly October 26, 2011 at 12:19 am

what’s the math look like if you split the batch and run off 2/3 of the volume for your 1st runnings and 1/3 of the volume for the 2nd runnings? Based on a SG 1.060. I am brewing this beer this weekend with our club it will be a 30 gal. batch the first 20 gal. should be 1.090 I figured the last 10 gal. should be 1.040 Would that be right?

James Howat December 12, 2011 at 2:20 pm

I’ve actually thought about doing this before with split batches but I didn’t know it had a name and could actually be done with some success. Definitely very interesting, although I’m not really clear on the advantages. I’ll have to try it and report back. Thanks!

alex December 26, 2011 at 4:02 am

Better have an extra propane tank on hand..or your in for a long brew session.

Luke May 14, 2012 at 1:25 pm

It would be wonderful if Beersmith supported parti-gyle brewing recipes in the software. Are there plans for this? My standard brewing procedure is to brew 11.5 G batches, and then ferment in 2 different fermenters changing one of the variables (yeast, hops, temp, etc.) It’s always a weird thing for me to have an 11.5 G recipe that isn’t reflective of the beer I brewed. The recipe will show 2 yeasts in it, but it combines the two in the recipe, or it shows them both in the yeast starter, etc. The same thing for dry hop additions.

Simon August 16, 2012 at 12:38 pm

Great article!

Rusty November 14, 2012 at 8:37 pm

Same question as Luke…. When will Beersmith support parti-gyle brewing?

Luke July 18, 2013 at 3:21 pm

On 06-24-2013, Brew Strong (on The Brewing Network) did an episode on Parti-gyle brewing, and the specifically mentioned that they were going to ask Brad Smith to support this feature in the software. Hopefully that helps the feature get bumped up the feature request list. I’m a little less interested in this feature for Parti-Gyle than I am for split batches with yeast or dry-hopping differences, but it seems that the features needed could support both.

DTB February 15, 2015 at 12:13 pm

Same as Luke – Sounds like we have the same setup and use Beersmith the same way…

Steven February 22, 2015 at 2:48 pm

As a brewer with only one burner, I’d have to store the 2nd running until the first boil is complete. It mentions saving the 2nd running in a sterile container for a few hours. Would it be possible to store it in a sterile carbon in a fridge for a week?

Leave a Comment

{ 5 trackbacks }

Previous post:

Next post: