One Batch, Many Beers: Experiment with Split Batches

I spent 10 years homebrewing batches of 5 gallons (19 L) and smaller. I reasoned that I was already brewing more beer than I could drink, so why buy a larger mash tun and kettle? The answer finally clicked when I came to embrace split batches. Brewing 10 gallons (38 L) doesn’t take anywhere near twice the time or effort of 5 gallons (19 L) because so much of the process isn’t volume dependent (e.g., starch conversion, hop isomerization, and fermentation). While you may spend a few more minutes milling the grain or heating the wort, split batches result in less frequent brew days with the associated reduction in the number of set-ups and clean-ups. As an aside, there is nothing to say you need to brew big batches to split. A two-gallon (7.6 L) brew can be split into two 1-gallon (3.8 L) jugs.

More important than process economies, splitting offers real educational advantages. When performing an experiment, a split batch allows for perfect process control. You can compare two yeast strains without the influence that a missed gravity or mash temperature would have if you re-brewed the recipe. You’ll be surprised by how much you learn from tasting your favorite recipe fermented with your standard yeast next to another strain.

I find constraints foster creativity: Forcing compromises, unique combinations, and hybrid styles. There have been numerous Great American Beer Festival (GABF) medals won by sour beers that started with the wort from of a brewery’s clean beer, before being aged in barrels with a variety of microbes, with or without fruit. Captain Lawrence Brewing Co. of Elmsford, New York won a gold medal in 2007 at the GABF for their Cuvee de Castleton – a pale sour crafted from Liquid Gold (their Belgian blond) then aged in wine barrels on Muscat grapes. Not to mention all of the grapefruit IPAs, coffee porters, and Bourbon barrel stouts!

Split batches can be divided at the mash, boil, and fermentation stages, or even as late as bottling or kegging. The further into the batch you wait, the more work saved. Think of it like carpooling: Share a ride with someone who lives near you, not someone who starts at the same spot but immediately drives in the opposite direction.


Your earliest opportunity to turn one brew day into two beers is at the mash. The time savings are minimal compared to a double brew-day because you’ll need to perform separate boils, chillings, and fermentations.

Parti-gyle (or combined grist brewing) is an historic English technique for getting stronger and weaker beers from a single mash. You could follow that model to harvest a special bitter from the leftover sugars trapped in the mash after running-off an English barleywine. There are plenty of other styles where the grain selection only differs by total amount: Wee heavy and Scottish light, or double IPA and American pale ale. Start with enough water in the mash tun to collect your target pre-boil volume for the stronger batch accounting for losses. As a rule of thumb, the first 13 of the wort collected contains about 23 of the fermentables. I find it helpful to take gravity readings and blend wort as needed between the first and second runnings to achieve the desired gravity for each wort. From there proceed with separate boils. In modern commercial parti-gyle the blending occurs post-boil to create more than two beers.

Rather than have two beers with identical grists, add crystal or roasted malts to the mash tun along with the sparge water to give the smaller beer more character or color. This technique is referred to as capping the mash. After collecting the wort for a 10% ABV triple IPA, I added some Weyermann Carafa® Special II and collected wort for a black IPA. Cutting edge for 2006 I thought!


Splitting the boil can be as simple as running half of the collected pre-boil wort into a second kettle to receive different hop additions. The first time I did this was to create five single-hopped beers. After 45 minutes of boiling all of the wort without hops I successively ran 1 gallon (4 L) off to boil with a single hop variety at a time for 15 minutes. It was grueling, but enlightening.

Whenever I brew a hefeweizen, I’ll run off half pre-boil once the wort reaches 175 °F (79 °C) and pitch my favorite combination of Berliner weisse microbes (Safale US-05, Lactobacillus brevis or L. plantarum, and fruity Brettanomyces). This is considerably easier if you use an in-line chiller. I’ve yet to brew a true raw ale, but running half of the wort directly from the mash tun into a fermenter would be a low-effort way to start!

I frequently brew IPAs and saison split batches. The movement towards lower bitterness IPAs with unmalted grain instead of crystal malt results in a wort nearly identical to that of a saison. I start with 30 IBUs near the beginning of the boil and collect the wort for the saison either before or after adding the whirlpool hops (depending on how aromatic a beer I desire). I add salts directly to the fermenter if I want dissimilar water profiles for the two beers.

As an alternative to parti-gyle to create stronger and weaker beers, you can dilute a portion of the wort before fermentation (or even after fermentation if you use deaerated water). When I brewed a batch inspired by Ron Pattinson’s recipe for 1883 Guinness Extra Stout in The Homebrewer’s Guide to Vintage Beers, I diluted 3 gallons (11.4 L) of the 1.075, 73 IBU wort with 2 gallons (7.6 L) of distilled water post-boil. The result was akin to modern Guinness Draught at 1.047 and 44 IBUs, but with a richer malt and hop profile.


For styles so different, Pilsner and saison can be identical before fermentation. I brewed a wort with 100% Pilsner malt and Saphir hops (an intensely herbal and spicy German variety). Half fermented cold with White Labs Pilsner Lager, and the other half 30 °F (17 °C) warmer with a Wyeast Saison-Brett Blend. I dry hopped both with more Saphir. A fun pair to serve side-by-side to let friends taste how much of a difference fermentation makes! This is an easy way to start dabbling with mixed-fermentation, even if you only divert a single gallon (3.8 L).

When brewing purpose-designed sours I always pitch different microbes into the two fermenters. I can blend them back together at bottling to taste, or decide that one would be better with fruit while the other is perfect as is . . . or as drain cleaner.


If your fermenter can hold the whole batch, there are easy options for splitting once the yeast has done its job. Leave half plain while the remainder goes into a small barrel, ages on oak cubes or fruit, or infuses with hops or spices. There are hundreds of sugars to try out; do a split batch! I added five different varietal honeys to five 1-gallon (4-L) jugs before racking young pale sour into them. I turned 10 gallons (38 L) of adambier into 5 gallons (19 L) with maple syrup and Bourbon and the rest with dark candi syrup and calvados.

I’ll often wait until 5 gallons (19 L) of sour beer is ready to bottle, but only bottle half, racking the rest onto fruit in a 3-gallon (11.4 L) carboy. It is incredibly educational to sample the same beer as straight lambic and kriek. You could do the same with roasted squash, cocoa powder, vanilla, and cinnamon to turn half of a porter into a harvest delight!

Turn half of a pale beer dark by adding a cold extraction of dark malts. A helles into a schwarzbier, or IPA into a black IPA? Steep finely milled dehusked dark malt (e.g., Weyermann Carafa® Special II) in cool water overnight, strain, boil, cool, and dose to taste. The lazier approach is to add commercial products like Sinamar® or Maltoferm®.


One of my favorite things about kegging is the ability to alter the batch even part way through drinking it! A temporal split! Not hoppy enough? Bag and weight hops and drop them in. Stout needs more coffee notes? Pour in cold brewed coffee. Sour beer too sour? Add sweetness with fruit juice.

Saison not spicy enough? Dose with a ginger and peppercorn tea.

Sample the beer from the tap and perform a few trials to determine the perfect ratio before adding the flavoring to the keg. Even if you don’t keg, hop teas (or cones) can be dosed into single bottles, you can even pour half of a bottle into two glasses and add tea, tincture, juice, wine, or another beer into the other!


The hundreds of malts, yeasts, and hops that internet-enabled homebrewers can access tend to be overwhelming. Splitting allows me to sample and evaluate some of this variety without losing focus. Splitting batches causes me to brew recipes that I wouldn’t otherwise try. Some examples: Adding a little more bitterness to a saison because the split half is a German Pilsner, or making a Berliner weisse with 20% flaked oats because that’s what I wanted for the New England IPA. Splitting also lends perspective, allowing you to taste a version of the same beer with only a single variable changed.

Issue: December 2017