Converting to Partial Mash
Partial-mash brewing combines many of the best aspects of extract and all-grain brewing. You can brew a partial-mash beer on your stovetop — with, at most, only minor changes to an extract-based brewing setup — yet you can also explore a wide world of base malts and make a large portion of your wort “from scratch.” One of biggest drawbacks to partial-mash brewing is the relative dearth of homebrew recipes that use this method. However, as I’ll show in this article, most extract or all-grain recipes can easily be converted to a partial-mash formulation.
In partial-mash brewing, the brewer makes wort from mashing malted grains (as all-grain brewers do), but then supplements this wort with malt extract to reach his target original gravity. Most partial-mash brewers boil less than their total volume of wort (as stovetop extract brewers do), diluting it to working strength in the fermenter. In many ways, partial mashing is similar to making an extract beer supplemented with steeped specialty grains. The big difference is, in partial mashing, base malts are mixed along with the specialty malts and the temperatures and volumes of brewing water used in the “steep” fall into a narrower range.
Partial mashing offers several benefits to extract brewers. There is a wide variety of base malts available to all-grain brewers, all with different flavors and aromas. In contrast, there are relatively few light or pale malt extracts. Partial- mash brewing allows extract brewers to fine tune the base malt character of their beers by blending wort made from mashed base malts with their malt extract. Partial-mash brewing also yields beer with more malt aromatics, as some of the aromatic compounds from malt are lost when malt extract is concentrated. Steeping specialty grains, a common practice in extract brewing, helps compensate for this somewhat. However, malt aromas specifically from the base malt can be added when partial mashing. (Compare the aroma of pale or Pilsner malt at your homebrew shop to the aroma of the specialty malts you commonly steep; they aren’t the same.) Partial mashing can also help demystify the process of mashing, potentially helping an extract brewer decide if he wants to make the leap to all-grain brewing.
For all-grain brewers, partial mashing can be a way to schedule a shorter brew day — or a brew day away from inclement weather outdoors — while still yielding great beer.
No matter what type of brewer you are, you can likely use almost all of your favorite recipes in a partial-mash formulation. Converting a homebrew recipe to a partial-mash formulation involves either converting a certain amount of malt extract into malted grain or a certain amount of malted grain into malt extract, depending on whether your initial recipe is extract or all-grain. The amount of ingredients other than water (hops, kettle adjuncts, yeast, etc.) do not change. So generally, you are left with one simple calculation to convert your extract or all-grain ingredient list into a partial-mash ingredient list.
How Partial to Make Your Mash
Before you start converting recipes, you’ll need to decide how much grain you will be mashing. The volume required to mash a given weight of malted grain is given in Table 1 (below). For a 5-gallon (19-L) recipe, you should mash a minimum of 2 lbs. (0.91 kg) of grain (specialty malts and base malts combined). Below this amount and you aren’t going get many of the benefits of partial mashing. The maximum amount you can handle will likely depend either on the size of your brewpot or the size of your mashing vessel. And of course, if the size of your partial mash is such that you only use a very small amount of extract, you might as well go all-grain.
The amount of wort you collect from the partial mash goes up with the weight of the grains added. So, the size of your brewpot may limit the size of your partial mash. In partial mashing, the volume of wort yielded is about 20% larger than the volume of the mash. For example, in most of my own partial-mash recipes, I mash 4 lbs (1.8 kg) of grains in enough water to yield a 2-gallon (7.6-L) mash. After draining the first wort and sparging, I usually end up collecting just short of 2.5 gallons (9.5 L) of wort. Table 1 on page 66 gives an estimate of how much wort you will collect from a given grain bed and its specific gravity, when diluted to 5 gallons (19 L). How much hot water you rinse the grains (sparge) with is, of course, the biggest variable relating to the volume of wort collected. In practice, your numbers may differ, but those given in Table 1 are a good reference point for beginners.
In general, you should mash as much as you can. If you can mash, say, 6 lbs (2.7 kg) of grain, it really doesn’t make sense to mash only 5 lbs. (2.3 kg) — the differences in time and energy expended would be minimal. Plus, larger mash volumes fluctuate in temperature less than smaller volumes. In addition, malted grains are cheaper than malt extract, so the larger the partial mash, the cheaper your ingredient costs (although admittedly, the difference isn’t that substantial at the 5-gallon/19-L scale).
If you plan to mash in your brewpot, figure on having the mash fill about 66% percent (two thirds) of the brewpot. This makes it easier to control splashes and allows you to slowly lift the grain bag out with less chance of slopping wort onto your stovetop. And, as you will yield slightly more than that volume of wort for the boil, this still provides a nice buffer for boilovers For example, if you had a 5-gallon (19 L) brewpot, and were using that as your mash vessel, set your partial-mash volume to 3.3 gallons (12 L). This way, you will yield 4 gallons (15 L) of wort to boil.
If you are using a separate vessel for a mash/lauter tun, a very handy solution is a 2-gallon (7.6-L) or 3-gallon (11-L) beverage cooler. These will hold 4 lbs. (1.8 kg) or 6 lbs. (2.7 kg) of grain, respectively, and yield roughly 2.4 to 3.6 gallons (9.1–14 L) of wort — amounts that would work well for any brewer with a 5-gallon (19-L) brewpot. Plus, at that size, you will not need to modify the cooler in any way. Just place all the grains inside a grain bag and place it in the cooler. One drain hole (from the built in spigot) is plenty to drain the cross-sectional area of the vessel. The simple “grain bag in a cooler” method works well in coolers up to 5 gallons (19 L). Beyond that you’ll probably want to install some sort of manifold. An added benefit of using a cooler versus mashing in a pot is that there is no lifting bags of hot, wet grain and so splashing is minimized.
Converting Extract Recipes
If you want to convert a malt-extract-based recipe to a partial-mash recipe, first check on the type of malt extract called for in the recipe. If it is a “straight,” unblended malt extract, you are in business. By “straight” malt extract, I mean any malt extract that is not made from a blend of different malts. Dark malt extract and amber malt extract are two types of malt extract made from more than one kind of malt. In the absence of knowing the types of malt and their proportions in the extract, you cannot make a good conversion to a partial-mash recipe.
On the other hand, if the malt extract used is light (or extra light) malt extract, pale malt extract or Pilsner malt extract, you are fine. Likewise, wheat malt extract and Munich malt extracts are blends, but generally the proportion is 50% wheat malt or Munich malt to 50% pale barley malt, so again you can make the conversion, albeit with a couple added calculations. In a like manner, most extracts designed to make American-style Pilsners are blends, but the blend ratio is usually in the ballpark of 30–40% corn or rice and 60–70% barley malt.
So, you’ve got your extract recipe with an unblended malt extract and have decided on the size of your partial mash. Now, all you need to know is how to convert a portion of the malt extract to the appropriate base malt.
The Steps To Do This Are:
1. Decide on the volume of your partial mash and the corresponding weight of your grains.
2. Subtract the weight of the specialty grains from the partial-mash weight.
3. Add this amount of the appropriate base malt to reach your partial-mash weight (based on extract type).
4. Decrease the amount of malt extract corresponding to the weight of the added base malt times the potential extract of the base malt divided by the potential extract of the malt extract. (See Table 2, below, for representative numbers for potential extracts for common base grains and malt extract types.)
Extract Example:
As an example, let’s say you had a Bohemian Pilsner recipe that called for 0.5 lb. (0.23 kg) of light crystal malt (20 °L), 8.5 lbs. (3.9 kg) of light, liquid Pilsner malt extract, 40 IBUs of Tettnanger bittering hops and lager yeast. To convert the recipe, leave the amount of specialty malts (in this recipe, the crystal malt) and all the other ingredients alone and focus on the Pilsner malt extract. Let’s say you have decided that you are going to mash 4 lbs. (1.8 kg) of grains. Subtracting the weight of the specialty grains (0.5 lb./0.23 kg) from 4 lbs. (1.8 kg) yields 3.5 lbs. (1.6 kg) of grain needed in the recipe. Given that you used Pilsner malt extract, that 3.5 lbs. (1.6 kg) of malt will be Pilsner malt and you have now completed the partial- mash portion of your ingredients list. The only thing remaining is how much Pilsner malt extract to delete from the initial recipe. Malt extract and grain cannot be swapped 1:1 on a by weight basis. (In this example, you can’t just subtract 3.5 lbs. (1.6 kg) of malt extract for the 3.5 lbs. (1.6 kg) of Pilsner malt in the partial mash.) You need to take into consideration their extract potential — a measure of how much they increase the specific gravity of a solution per weight of the ingredient added. (See Table 2, below, for a list.)
To calculate the weight of malt extract to subtract, multiply the weight of the malted grain by its extract potential divided by the extract potential of the malt extract. In this case, 3.5 lbs. * (37 ppg/33 ppg) = 3.9 lbs. of malt extract. As such, your final ingredient list would be 0.5 lb. (023 kg) crystal malt (20 °L), 3.5 lbs. Pilsner malt (for a total of 4 pounds of grain to mash), 4.6 lbs. (2.1 kg) of liquid Pilsner malt extract, plus the hops and the yeast from the original recipe.
Converting All-Grain Recipes
Converting an all-grain recipe to a partial mash formulation is simple. Assemble your partial mash by combining all of the specialty grains the recipe calls for plus whatever base malt will be needed to reach your intended partial-mash weight. Then convert the remaining base malt to malt extract. In this case, you will multiply the remaining amount of base malt by its potential extract, then divide by the potential extract of the malt extract. The rest of the ingredient list remains the same. Only the procedures change.
Of course, you can only make this conversion if there is a malt extract equivalent of your base malt. If the recipe calls for 2-row pale malt, 2-row pale ale malt or just “pale malt,” use pale, light or extract-light malt extract. There are Pilsner malt extracts for Pilsner malts and malt blends for some other types of base malt. As mentioned before, Munich malt extract is usually made from a 50:50 blend of Munich and pale (or often Pilsner) malt and wheat malt extract is usually made from a 50:50 blend of wheat malt and pale malt.
All-grain recipes should include a mash program — what temperature rests are used and for how long (and sometimes the mash thickness is also given). One obvious approach to partial mashing would be to follow the mash program specified in the all-grain recipe. For simplicity’s sake, this should be your choice if the recipe specifies a single-infusion mash. If the recipe specifies a step mash, decoction mash or other mash program, you’ll need to decide if you want to duplicate that in your partial mash, or simplify the instructions and perform a single-infusion mash. Part of that decision will be based on your set-up. If you are using an insulated cooler as a mash tun, you can’t do any mash program that calls for directly heating the mash. Step mashes generally take longer than a single-infusion mash when all the rests are added up (especially when heating times are added) and they result in wort with a higher fermentability than a single-infusion mash with the same saccharification temperature. So, if you simplify a step mash down to a single rest, pick a temperature near the bottom of the range for single-infusion mashes — 148–150 °F (64–65 °C).
Also, for beers you want to be dry, try this trick. Run off your wort and hold it in the low end of the saccharification range (148–162 °F/64–72 °C). Then stir in your malt extract (or at least the first addition, if you are withholding some for late in the boil) and hold the mixture at 148–150 °F (64–65 °C) for 5 minutes before you begin to heat the wort. This allows the enzymes from the malted grain to work on any carbohydrates in the malt extract that could be reduced to simpler sugars.
All-Grain Example:
For the all-grain example, let’s pick a recipe for which we’ll have to use a blended malt extract. Specifically, let’s say we have a wheat beer recipe that calls for 70% Pilsner malt (7 lbs./3.2 kg), 30% wheat malt (3 lbs./1.4 kg). If we are using a 4-lb.(1.8-kg) partial mash, which base malt or combination of base malts do we choose? We know that we will be using wheat malt extract for the malt extract and that it is made with 50:50 wheat malt to pale malt, so we’ll want the portion of the grain bill converted to extract to be as close to 50:50 as possible with regards to the two types of malt. A quick look shows that using 4 lbs. (1.8 kg) of Pilsner malt leaves a 50:50 blend of the two base malts. This is perfect, but what if we want some of the aroma from the wheat malt?
Let’s say we make the partial mash out of 3 lbs. (1.4 kg) of pale malt and 1 lb. (0.45 kg) of wheat malt — close to the initial ratio in the all-grain recipe (but rounded to the nearest pound to make the example calculations simpler to follow). This leaves 2 lbs. (0.91 kg) of wheat malt and 4 lbs. (1.8 kg) of Pilsner malt to convert to malt extract. To do this, we need to break the malts up into two portions — a portion to be converted to wheat malt extract and a portion to be converted to Pilsner malt extract. If we take the 2 lbs. (0.91 kg) of wheat malt pair it with 2 lbs. (0.91 kg) of Pilsner malt, we can convert this to wheat malt extract; then we simply convert the remaining Pilsner malt to Pilsner malt extract. This would leave us with a grain bill of 1 lb. (0.45 kg) Pilsner malt, 3 lbs. (1.4 kg) wheat malt, 3.4 lbs. (1.5 kg) dried wheat malt extract and 2 lbs. (0.91 kg) liquid Pilsner malt extract.
You can increase the flexibility of your brewing program by including partial-mash methods in your set of skills.
Types of Partial Mashing
Homebrewing equipment set ups, and the methods used with them, are highly varied. Nowhere is this more true than with brewers who use partial-mash methods. This is a survey of some of the ways homebrewers approach partial mashes and the strengths and weaknesses of each. The first approach is both simple and flexible — place all the grains you will be mashing in a large steeping bag and mash in your brewpot. The mash can be kept on the stovetop and heated and stirred occasionally, or the brewpot can be insulated with towels. Some brewers even turn their oven on its lowest setting, open the door and place the brewpot inside. A big strength of this method — besides the fact that all you need beyond your basic extract brewing equipment is a large steeping bag — is that you can heat the mash directly on your stovetop. You could even do step mashes if you wanted. A variation on this is to mash your grains in a separate pot. You could do this on the stovetop, insulated with towels or in the oven as with the brewpot. The strength to this method, assuming you have a kitchen pot big enough to hold your mash, is that you can be heating the water in your brewpot as the mash rests. In fact, you can steep dark specialty grains (if your recipe calls for them), in your brewpot while mashing pale malt in your secondary pot. A third approach involves using an unmodified beverage cooler as a small mash tun. Although you cannot heat this mash directly, containing the mash in a cooler and draining it via the spigot eliminates the need to lift bags of hot grain out of your mash pot and into a colander to be rinsed.
Partial-Mash Recipes
Poe’s Boston Bitter
(5 gallons/19 L, all-grain)
OG = 1.037 FG = 1.009
IBU = 33 SRM = 9 ABV = 3.6%
“Fill with mingled cream and amber, I will drain that glass again.
Such hilarious visions clamber through the chambers of my brain.
Quaintest thoughts – queerest fancies, come to life and fade away:
What care I how time advances? I am drinking ale today.”
– Edgar Allan Poe
Ingredients
7 lbs. (3.2 kg) British 2-row pale ale malt
0.5 lb. (0.23 kg) crystal malt (60 °L)
7.5 AAU Kent Golding hops (60 min.) (1.5 oz./43 g at 5% alpha acids)
2.5 AAU Kent Golding hops (10 min.) (0.5 oz./14 g at 5% alpha acids)
2.5 AAU Kent Golding hops (5 min.) (0.5 oz./14 g at 5% alpha acids)
0.5 oz. (14 g) Kent Golding hops (0 mins)
0.5 oz. (14 g) Kent Golding hops (dry hop)
Wyeast 1028 (London Ale) or White Labs WLP026 (Burton Ale) yeast (1 qt./1 L yeast starter)
3/4 cup corn sugar (if priming)
Step by Step
Mash at 153 °F (67 °C). Boil for 60 minutes, adding hops at times indicated. Pitch yeast and ferment at 68 °F (20 °C). After primary fermentation has ceased, let beer set for 2 days, then rack to secondary and add dry hops. Dry hop for 1 week.
Poe’s Boston Bitter
(5 gallons/19 L, partial mash)
OG = 1.037 FG = 1.009
IBU = 33 SRM = 9 ABV = 3.6%
Ingredients
3.5 lbs. (1.6 kg) British 2-row pale ale malt
0.5 lb. (0.23 kg) crystal malt (60 °L)
2 lbs. (1.4 kg) light dried malt extract
7.5 AAU Kent Golding hops (60 min.) (1.5 oz./43 g at 5% alpha acids)
2.5 AAU Kent Golding hops (10 min.) (0.5 oz./14 g at 5% alpha acids)
2.5 AAU Kent Golding hops (5 min.) (0.5 oz./14 g at 5% alpha acids)
0.5 oz. (14 g) Kent Golding hops (0 mins)
0.5 oz. (14 g) Kent Golding hops (dry hop)
Wyeast 1028 (London Ale) or White Labs WLP026 (Burton Ale) yeast (1 qt./1 L yeast starter)
3/4 cup corn sugar (if priming)
Step by Step
Mash grains at 153 °F (67 °C) for 45 minutes in 7.8 qts. (7.5 L) of water. Sparge grains to yield just short of 2.5 gallons (9.5 L) of wort. Add water to make 3 gallons (11 L) and add roughly one third of the malt extract. Boil wort for 60 minutes, adding hops at times indicated. Add remaining malt extract for final 15 minutes of boil. Cool wort and transfer to fermenter. Top up to 5 gallons (19 L) with cool water and pitch yeast. Ferment at 68 °F (20 °C). After primary fermentation has ceased, let beer set for 2 days, then rack to secondary and add dry hops. Dry hop for 1 week.
Extract with Grains Option:
Reduce amount of pale ale malt to 1.5 lbs. (0.68 kg) and increase amount of light dried malt extract to 3 lbs. (1.4 kg). Steep grains at 153 °F (67 °C) in 2.8 qts. (2.6 L) water for 45 minutes. Add water to make 3 gallons (11 L) of wort and add roughly one third of the malt extract. Boil wort for 60 minutes, adding hops at times indicated. Add remaining malt extract for final 15 minutes of boil. Cool wort, transfer to fermenter and top up to 5 gallons (19 L) with cool water. Pitch yeast and ferment at 68 °F (20 °C). After primary fermentation has ceased, let beer set for 2 days, then rack to secondary and add dry hops. Dry hop for 1 week.
Tips for Success:
Both the extract and all-grain versions convert into the partial-mash version of this recipe. Some 2-row pale ale malt is converted to light dried malt extract in the all-grain to partial-mash conversion; the opposite in the extract to partial-mash case. This beer is named for Edgar Allen Poe. This Boston-born writer, whose short stories of mystery and the macabre are still enjoyed today, was a fan of ale. This British-style bitter is well-suited to a partial-mash formulation as two thirds of the extract weight comes from grain. For best results, use fresh malt extract. This beer will condition quickly. You can easily be draining your glass 13 days after brewing.
Old Cthulhiar (a.k.a. Very Old And Very Peculiar)
(5 gallons/19 L, all-grain)
OG = 1.078 FG = 1.017
IBU = 41 SRM = 32 ABV = 7.8%
Ingredients
13 lbs. (5.9 kg) British pale ale malt
8 oz. (0.23 kg) crystal malt (60 °L)
2 oz. (57 g) crystal malt (120 °L)
5 oz. (0.14 kg) aromatic malt
3 oz. (85 g) chocolate malt
2 oz. (57 g) black malt
3 oz. (85 g) molasses
12 oz. (0.34 kg) cane sugar
9 AAU Northern Brewer hops (60 min.) (1 oz./28 g at 9% alpha acids)
5 AAU Fuggles hops (15 min.) (1 oz./28 g at 5% alpha acids)
1 oz. (28 g) Fuggles hops (2 min.)
0.5 oz. (14 g) Fuggles whole hops (dry hop)
Wyeast 1028 (London Ale) or White Labs WLP026 (Burton Ale) yeast (2 qt./2 L yeast starter)
3/4 cup corn sugar (if priming)
Step by Step
Mash at 152 °F (67 °C). Boil for 75 minutes, adding hops at times indicated. Add sugar with 15 minutes left in the boil. Pitch yeast and ferment at 68 °F (20 °C). After primary fermentation has ceased, let beer set for 3 days, then rack to secondary and add dry hops. Dry hop for 2 weeks. Let age for 6 months.
Old Cthulhiar (a.k.a. Very Old And Very Peculiar)
(5 gallons/19 L, partial mash)
OG = 1.078 FG = 1.017
IBU = 41 SRM = 32 ABV = 7.8%
Ingredients
4 lbs. (1.8 kg) British pale ale malt
8 oz. (0.23 kg) crystal malt (60 °L)
2 oz. (57 g) crystal malt (120 °L)
5 oz. (0.14 kg) aromatic malt
3 oz. (85 g) chocolate malt
2 oz. (57 g) black malt
5 lbs. (2.3 kg) light dried malt extract
3 oz. (85 g) molasses
12 oz. (0.34 kg) cane sugar
9 AAU Northern Brewer hops (60 min.) (1 oz./28 g at 9% alpha acids)
5 AAU Fuggles hops (15 min.) (1 oz./28 g at 5% alpha acids)
1 oz. (28 g) Fuggles hops (2 min.)
0.5 oz. (14 g) Fuggles whole hops (dry hop)
Wyeast 1028 (London Ale) or White Labs WLP026 (Burton Ale) yeast (2 qt./2 L yeast starter)
3/4 cup corn sugar (if priming)
Step by Step
Mash pale malt at 153 °F (67 °C) for 45 minutes in 7.8 qts. (7.5 L) of water. Sparge grains to yield just short of 2.5 gallons (9.5 L) of wort. While mashing, steep specialty grains in 2 qts. (~2 L) of water in your brewpot at 153 °F (67 °C). Add wort from partial mash to steeping liquid in your brewpot and add roughly one third of the malt extract. Boil wort for 75 minutes, adding hops at times indicated. Add sugars and remaining malt extract for final 15 minutes of boil. Cool wort and transfer to fermenter. Top up to 5 gallons (19 L) with cool water and pitch yeast. Ferment at 68 °F (20 °C). After primary fermentation has ceased, let beer set for 3 days, then rack to secondary and add dry hops. Dry hop for 2 weeks.
Extract with Grains Option:
Reduce amount of pale ale malt to 0.75 lbs. (0.34 kg) and use a total of 6.75 lbs. (3.1 kg) light dried malt extract. Steep grains at 152 °F (67 °C). Add roughly one half of the malt extract and boil wort for 75 minutes, adding hops at times indicated. Add sugars and remaining malt extract for final 15 minutes of boil. Cool wort and transfer to fermenter. Top up to 5 gallons (19 L) with cool water and pitch yeast. Ferment at 68 °F (20 °C). After primary fermentation has ceased, let beer set for 3 days, then rack to secondary and add dry hops. Dry hop for 2 weeks. Age for 6 months.
Tips for Success:
The partial-mash fomulation of this beer utilizes steeped specialty grains (in the brewpot) and a separate small mash. This beer is a darker, stronger and more bitter interpretation of Theakston’s Old Peculiar. It gets its name from Cthulhu — a central character (one of the Old Ones) in H. P. Lovecraft’s writings. For best results, make a 2-qt. (2-L) yeast starter and pitch the yeast from this. This is underpitching, compared to the optimal pitching rate, but is done intentionally to help the yeast develop an estery character that is appropriate for this beer.
