Brew 15 Gallons (57 L), Fast


A diagram of the method. (Click to enlarge.)

If you have a 5.0-gallon (19-L) brewery, but want to generate 15 gallons (57 L) of beer quickly — perhaps for a party — here’s one way to do it. Normally, this would require three separate brew days. However, with the method I described here, you can do it in two brew days — and only have to make one yeast starter.

The drawbacks are that the two brew days need to be back to back, all 15 gallons (57 L) will be of the same kind of beer, and the beer can’t be over 13 °Plato (OG 1.052). Also, you will want to consume the beer fairly quickly (within a couple months), as it will go stale faster than normal homebrew. This method is best for generating 15 gallons (57 L) of beer for a party.

The Basic Idea

Especially, what you do is produce 6.0 gallons (23 L) of wort, and get it fermenting in a 7.0-gallon (26-L) bucket fermenter. This wort will be 1.25 times the desired working strength. For example, if you’re making a 12 °Plato (OG 1.048) beer, your wort will be 15 °Plato (OG 1.060). The next day, you brew another 6.0 gallons (23 L) of fresh, 1.25X wort. Then, you split the fermenting wort into two buckets and top them up with the freshly made wort — for a total of 12 gallons (45 L) of fermenting strong beer. Once the strong beer is fermented, you transfer 4.0 gallons (15 L) each to three 5.0-gallon (19-L) Corny kegs. You then add 1.0 gallon (3.8 L) of deaerated water to each keg to make 5.0 gallons (19 L) of working-strength beer. The full procedure is given below. To do this, you will need brewing equipment capable of producing 6.0 gallons (23 L) of wort, two 7.0-gallon (26-L) fermentation buckets, and three 5.0-gallon (19-L) Corny kegs. You can substitute a bottling bucket and seven cases of 12-oz. (355 mL) beer bottles for the Corny kegs.


The Procedure

If you plan to do this, start with your recipe. Formulate a 15-gallon (57-L) recipe as if you were going to brew it in a single brew day. Next, divide all the ingredient amounts in the recipe, except for the yeast and water, by 2. This half recipe will be your recipe for each of the two brew days. You will only need to build a yeast starter for the first day. (You will need a yeast starter big enough to pitch 6.0 gallons (23 L) of wort at 1.25 times your working strength OG.)

Your half recipes will contain all the ingredients for 7.5 gallons (28 L) of beer. However, you will brew them at 6.0 gallons (23 L). In other words, you wort will be 1.25 times thicker than if you made it at working strength. Make your first batch of wort and pitch the yeast. Hopefully, it will be strongly fermenting by the time you start producing your second batch. The best time to produce the second batch is 16 to 24 hours after the first.

It’s best to ferment the beer in buckets, because the first batch of fermenting beer needs to be split between two fermenters on the second brew day. It’s hard to siphon actively fermenting beer, but very easy to simply pour it into a second bucket.

Your second brew day will be exactly like your first. Make the 6.0 gallons (23 L) of wort, and chill it. Transfer half of your fermenting beer to the second bucket. Before splitting up the fermenting beer, take a sanitized spoon and stir it so all the solids at the bottom of the fermenter get suspended. Try to get matching amounts of trub in each of the two fermenters, but don’t worry too much about it. Then, add fresh wort to both the buckets to fill them to the 6.0-gallon (23-L) mark. If the wort from the first day is fermenting vigorously, you will not need to aerate the fermenting beer mix at this point. If the wort from the first day is not fermenting vigorously, aerate the mix. Be absolutely sure your second batch of wort is cooled to fermentation temperature before mixing it with the previously fermenting beer.

Let the two buckets of beer ferment to completion. Then, let it sit — at fermentation temperature — for a few days. Because you disturbed the fermentation on the second day you made wort, the yeast may have produced more diacetyl than usual. The two to three day rest after fermentation should allow the yeast to take up any residual diacetyl.



After fermentation, you will have two 6.0-gallon (23-L) batches of strong beer. You will split them equally into three 5.0-gallon (19-L) Corny kegs. To blend away any differences between batches, you could add 2.0 gallons (7.6 L) to each of the Corny from each of the two buckets. (On the other hand, if you dry hopped one of the buckets, you could make three beers with different levels of dry hopping in the three kegs.) Finally, you would add 1.0 gallon (3.8 L) of deaerated water to each keg, seal it, and proceed to carbonation.

To make the deaerated water, start with around 3.5 gallons (13 L) of water and boil it hard for about 15 minutes. Cool the water quickly and transfer it to the kegs. If possible, bubble some CO2 through the water after it has been boiled. (For more on the rationale behind deaerating the water, and why this won’t work for bigger beers, see my article, “Expand Your Output.”)

If you don’t have three kegs, you can bottle the beer in four shifts if you have a bottling bucket. (You could cut this to two shifts if you had a 7.5-gallon (28-L) bottling bucket.) In each shift, you will bottle 3.75 gallons (14 L) — a mix of 3.0 gallons (11 L) of strong beer and 3.0 qt. (2.8 L) of deaerated water. In each shift, you will fill forty 12-oz. (355 mL) bottles or twenty two 22-oz. (650 mL) bottles. Use a carbonation calculator to determine how much priming sugar to add. For an ale carbonated to average craft beer levels of carbonation, somewhere around 3.75 oz. (110 g) per shift will give the right amount of fizz. You can add the carbonation sugar to the deaerated water will you are boiling it.



One the beer is packaged, treat it as you normally would. However, be aware that it will likely go stale a little faster than normal homebrew, because it’s impossible to completely deaerate water simply by boiling. The beer should be in peak condition for two or three months, but then start showing signs of going stale. If you brewed this for a special event, and it all gets consumed there, then you do not have to worry. Storing the beer cold will help to keep it in good condition longer.



If you have a 5.0-gallon (19-L) brewery that you can squeeze 6.0 gallons (23 L) out of, you can make the equivalent of three brew days worth of beer in two brew days. You do have to boil some water when packaging, but you only have to make a yeast starter once, so you do end up with some time savings. (Also, if fermenter space is at a premium, this requires only two fermenters, not three.)

I did something very similar to this when I brewed beer for my wedding rehearsal dinner. (I threw in the added twist of bottling a small amount of the strong beer, then doing a serial dilution to make three different strength beers from the same recipe.) The beer was packaged a couple weeks before the event, but was still in fine shape for the dinner. A few bottles that were left over remained in good condition for a few weeks . . . and then they were gone. So, I don’t know how long it could have stayed in good shape. As I was brewing on the stovetop in my apartment, and had a limited number of fermenters, this method helped me output more beer than I could have had I brewed it all at working strength.


Related articles

Expand Your Output

Brewing for Special Events

Blending Beers



  1. Alexander Gashti says

    Is it possible to provide a recipe Chris? Maybe something other than light lager. This would help me conceptualize high gravity, then dilution to the final volume.


  2. Emperor Pho says

    It is the anti parti gyle.

    • Chris Colby says

      Yep, it is, in a way. Instead of yielding two or more kinds of beer from one brew day, you yield one kind of beer from two brew days.

  3. I do something similar. I usually make what would basically be a Maibock but have also done a strong Pale Ale. I shoot for about 7% and a FG of 1.014-16. The difference is I ferment and carb as is. I dilute using deaerated and carbonated water the day before or even the morning of the event. This way staling isn’t an issue and I can serve it at the strength appropriate for the day.

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