Brew a Porter using a Partial-Mash

Making a partial mash of base grains improves the flavor of extract
beers. I’ll also show you how changes in some brewing procedures
require compensating changes in other procedures. And of course,
you’ll need a few new pieces of equipment — a bigger brew kettle
to hold the entire volume of wort, a device to quickly chill your hot
wort to pitching temperature, and an aquarium pump and aeration stone
to add oxygen to the wort.

In Homebrew 301, we’ll focus on brewing a British style of beer — porter. Porters are dark, malty beers that first were brewed in London as early as the 18th century. Stout
evolved from porters, and many porters have a slight bite from dark
roasted grains, though not to the degree that stouts do. The hop
bitterness in porters is well-balanced with the maltiness, with
neither predominating in most examples of this style. Redhook’s
Blackhook Porter and Sierra Nevada Porter are two excellent U.S.
porters. Samuel Smith’s Taddy Porter is an English porter that is
widely available in the States.

In this recipe, we’ll supplement the
malt extract we use with sugars from a partial mash. In mashing, the
starch in the center of malted grains is broken down into its
constituent sugars. Along with the base grains, which will supply
most of the fermentables from the partial mash, we’ll add some
roasted specialty grains. We’ll also learn the advantages of
boiling our entire wort, and the changes we’ll have to make in our
equipment and brewing procedures as a consequence.

Partial mashing

In our porter recipe, approximately 2/3
of the fermentable sugars will come from malt extract. The remaining
1/3 will come from grains. Mashing is a simple process, but one that
is often made to seem overly complex in some homebrewing texts. The
essence of mashing is simply soaking crushed grains in water. As the
grains soak, the water dissolves the starch in the grains. Enzymes
from the grain attack the starch and chop it up into its building
blocks, sugars. Once the starch is fully converted, the sugars are
rinsed from the spent grains.

As far as starch-conversion goes, a
partial mash works exactly like a full mash. However, since less
grain is used in a partial mash, handling the soaking and rinsing of
the grains is simpler and requires no special equipment beyond a mesh
grain bag and a measuring cup. Performing a partial mash is very
similar to steeping specialty grains. Gaining some experience with
partial mashing often encourages brewers to go on to try making an
all-grain beer.

Performing a partial mash

In a partial mash, you want to steep
the grains in a volume of water sufficient to cover them completely,
but not leave a lot of excess volume. For our porter we’ll steep 2
pounds of pale malt, plus the specialty grains, in 2 gallons of
water. This is a thinner mash than most full mashes, but that won’t
adversely affect our beer.

To begin the partial mash, gather the
crushed grains and place them in the nylon bag. Although we will be
holding the temperature of the mash at 150° F, we need to heat the
water to 160° F to start. This is because the temperature of the
mash will drop once the grains, which are at room temperature, are
added to the liquid. Once the grain bag has been submerged for a
couple minutes take the temperature of the water in the pot. As with
the steeped specialty grains, you should shut the bag and tie it to
the handles of your brew pot.
Try to hold the temperature as close
to 150° F as possible for 1 hour. To adjust the temperature of the
partial mash, add heat or cold water as necessary. When changing the
temperature, add only a little bit of heat or cold water, then stir
and retake the temperature. It’s easy to overshoot your temperature
mark, especially when heating.

As you heat a pot, it takes time for
the heat to travel through the metal and equilibrate. Thus, if you
heat the mash continuously until the thermometer reads 150° F, then
turn off the burner, the temperature will keep rising as heat from
the pot is transferred to its contents. To avoid this, heat in short
bursts, stir while heating, and wait a couple of minutes before
checking the temperature again. It’s not going to hurt the beer if
it takes you a little while to adjust the temperature, so be patient.

Rinsing the grains

After an hour, take a large kitchen
strainer and lift the bag out of the water. Let the liquid drain into
your pot. If possible, balance the strainer over the pot. If you
can’t do this, have a friend hold it. Open the drawstring or untie
the bag and expose the grains. Take a measuring cup and ladle water
from the pot over the grains. The water will run through the grains
and fall back into the pot. Keep doing this for 5 minutes or so. The
idea here is to rinse as much of the sugars from the grains as

Once you’re done rinsing the grains,
use your small kitchen strainer to remove as much solid matter as
feasible. Don’t spend more than 5 minutes doing this. Once the
large solid materials have been removed, add the liquid (wort) to
your large brew pot. (Before you do, give it a taste. Mmmm . . .
malty!) Your strainers should be clean, but they do not need to be
sterilized since the wort will be boiled after they are used.

Full-wort boil

In your large brewpot — it should
hold at least eight gallons of liquid — combine the wort from the
partial mash with water to make 5.5 gallons. Bring this to a boil,
then add the malt extract. Although our target is 5 gallons of wort,
we need more wort initially because some liquid will evaporate during
the one-hour boil. The amount that evaporates is dependent on the
amount of heat applied to the kettle. If you’re boiling on the
kitchen stove, the evaporation may be minimal; if you’re using a
propane burner, it may be considerable.

Boiling 5 gallons of wort is a large
task for most home stoves. A gas stove can probably bring this volume
of wort to a rolling boil. An electric stove may have problems
developing more than a sustained simmer. Also, the amount of time it
takes for the wort to come to a boil may be quite long. You may wish
to begin heating the additional water while you are performing the
partial mash. If your kitchen stove is having trouble boiling this
volume, close the lid partially. Another option is to move your home
brewery to the backyard and use a propane burner for the boil.

Two benefits of boiling the entire wort
are increased hop utilization and less wort darkening compared to
boiling a concentrated wort. When brewing a beer using a full-wort
boil, you need to add fewer hops to get the same level of hop
bitterness. This is because more hop bitterness is extracted in more
dilute worts. With a full-wort boil, you can also brew beers that are
much lighter in color than beers brewed with from a concentrated
wort. In thicker worts, the sugars caramelize much easier, darkening
the wort. This difference in color won’t be very visible in our
porter, of course.

Another change that a full-wort boil
will bring is the inability to pour the wort directly into the
fermenter. (Pouring boiling wort into a glass carboy, for example,
could crack the glass.) With no cold water to dilute the wort and
bring down the temperature, you will need to cool the wort first.
Then, given the large volume, it’s more convenient to simply siphon
the wort to the fermenter.

This drawback, however, has a hidden
benefit. Since siphoning the wort to a fermenter leaves behind
material on the bottom of the kettle, you don’t need to keep your
hops in a bag or tea ball. The hop debris will settle to the bottom
of the kettle during cooling. The clear wort can then be siphoned off
the hop material and hot break, the proteins, lipids and other
compounds that coagulate in the boil.

Cooling your wort

There are several ways to cool wort.
One way is to place the kettle in a sink or bathtub full of cold
water and ice. The drawback of this method is that you need to lift a
large volume of near-boiling hot liquid. Needless to say, this can
be a bit dangerous. You can avoid the potential hazard of spilling 5
gallons of hot wort by chilling it on the stovetop with a submersible
wort chiller.

A submersible wort chiller is a spiral
of copper tubing. This tubing is submerged in the wort and cold water
is run through it. Heat from the wort transfers to the cold water and
is carried out. The speed of cooling and the eventual temperature the
wort reaches depends on the temperature of the cooling water.
You can speed chilling by gently whirlpooling the wort. If the
submersible wort chiller is left undisturbed, the wort next to the
copper coils will quickly cool. However, the wort farther away from
the coils will cool much more slowly. The wort will move somewhat in
that cold wort will sink and warmer wort will rise. But, starting a
whirlpool will greatly enhance the amount of hot wort passing by the
copper coils and greatly enhance your cooling rate.

If you move your submersible wort
chiller in a circular motion, you will start the wort moving. As the
wort moves by the cool chiller, it cools. Hot wort is prone to
hot-side aeration, so try not to agitate it unduly. Induce a slow,
steady swirling motion by moving the wort chiller in a circle. Repeat
this motion every five minutes.

The wort chiller is usually sterilized
by submersing it in the wort for the final 15 minutes of the boil.
During this time, there is no water flowing through it. In fact, it’s
best not to connect the tubing until after you have turned off the
heat to the kettle. A logistical note: Connecting the tubing to your
sink faucet will probably require an adapter, since most wort
chillers are threaded to screw onto a garden hose connector.

Aerating the wort

Performing a full-wort boil
necessitates one other change in your brewing procedure; you need to
aerate your wort once it is cool. In Homebrew 101 and 201, we simply
added cold, aerated water to our concentrated wort to aerate it. Now
we can’t do that, because our wort is already at working strength.
Adding water would dilute it.

One of the simplest ways to aerate
cooled wort is by using an aeration stone attached to an aquarium
pump. Most aeration “stones” used in brewing are actually made of
stainless steel. Air is pumped into the stone, where it is forced out
through hundreds of tiny holes. Air from the aquarium pump should be
filtered, so you are not pumping airborne microorganisms into your
wort. Most homebrew shops sell aeration kits that include the stone
and a HEPA filter. Since the aeration stone and the tubing leading to
it will touch the wort, you must sanitize both before you aerate.

You can aerate your wort while it is
siphoning into your fermenter. Just put the aeration stone in the
fermenter and run the aquarium pump as you are siphoning. By the time
your fermenter is filled, the wort should have enough oxygen. If
you’d like, you can run the pump for another five or ten minutes.
However, keep an eye on the wort so the bubbles from the aeration
stone don’t make the wort foam over.

Bottling the entire batch

After the porter ferments for a week or
so in your primary fermenter, and then settles for another week in
your secondary fermenter, it’s time to bottle. We’ll do things a
bit differently this time. Instead of priming each bottle
individually with PrimeTabs, we’ll use batch priming in a bottling

To bottle this way, you need to siphon
your wort from your secondary fermenter into a sanitized bucket. Try
to minimize the amount of splashing when you transfer the beer. You
don’t want to oxidize the porter.

For 5 gallons of beer, use a sanitized
spoon to stir a solution of sugar water into your beer. Make the
sugar water by boiling 3/4 cup of corn sugar in 2 cups of water. Boil
for 15 minutes, then cool the solution to about room temperature and
stir it into the wort. Now, siphon the beer into bottles and cap them
as before. The sugar water works just like the PrimeTabs; it provides
a new source of fermentable sugar, which causes fermentation in the
bottle and creates carbon dioxide.

After a week at room temperature, put
the bottles in the fridge for a week. Then, invite some friends over
and impress them with your newfound brewing skills.


OG 1.048 FG 1.014 IBUs 26

3.75 lbs. dried malt extract (light, unhopped)
2 lbs. pale ale malt
3/4 lb. crystal malt
1/2 lb. chocolate malt
1/4 lb. black patent malt
9 AAU Fuggles hops
(2 oz. of 4.5% alpha acid)
Wyeast 1968
3/4 cup corn sugar for priming

4 days before brew day
Make yeast starter
Refrigerate yeast starter

3 days before brew day
Aerate starter
Pitch yeast to starter

On brewing day
Heat 2 gallons of water to 160° F
Steep all grains for 60 minutes
Hold temperature at 150° F
Rinse grains with hot water from brew pot
Strain out “floaties”
Add 3.5 gallons of water to mash water
Bring the 5.5 gallons of water to a boil
Stir in malt extract
Bring wort to boil
Add bittering hops
Cool wort with wort chiller
Siphon cooled wort to fermenter
Aerate wort with aquarium pump, stone and filter
Pitch yeast
Ferment for one week

1 week after brew day
Rack beer to secondary

2 weeks after brew day
Test specific gravity with hydrometer for 3 days
Bottle beer when gravity is constant
Condition at room temperature for 1 week
Refrigerate for 1 week

3 weeks after brew day
Beer is ready

Issue: September 2001