Decoction mash

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A decoction mash is a type of mash in which the various mash temperatures are achieved by removing part of the mash, boiling it in a separate vessel, and then using it as infusion water to heat the remainder of the mash. It is traditional in many continental European beer styles, especially in Germany and the Czech Republic.

Decoction mashing is not common among home brewers, since it has a reputation as a time and labor-intensive process. But a decoction mash is basically just a step infusion mash where some of the grist is heated along with the infusion water. While it does take some extra time and require some extra stirring, it is a procedure that can be performed by most home brewers.


[edit] History of the Decoction Mash

Decoction mashing refers to removing a part of the mash, boiling it and returning it to the main mash to increase its temperature to the next rest. This mashing procedure originates from a time when malt quality was not consistent and temperatures could not be measured. The long boiling of the grain makes the starches more accessible for the enzymes. This is particularly important for undermodified malts where the cell walls are not as broken down as they are in well modified or overmodified malts. The boiling of a defined portion of the mash and returning it to the main mash to raise the temperature also helped the consistency in mashing temperatures before thermometers were available.

[edit] Chemistry of the Decoction Mash

Today even most European malts are generally well modified and can be used in infusion step mashes or even single infusion mashes, thus removing the need for decoction mashing. But decoction mashing is still widely used, particularly in German brewing. Many brewers believe that the boiling of the mash gives the beer a flavor profile that cannot be achieved otherwise. But, especially in the home brewing community, there has been debate about the actual benefits of a mash as labor intensive as a decoction mash. Many say that with the malts that are available to the home brewer decoction mashing doesn't make for a difference and if there is a difference it could also be achieved by the use of specialty malts. But in the end every brewer has to determine that for him or herself.

[edit] Decoction Mash Procedure

The basic procedure for performing a decoction mash is very simple. Water is added to the grist to reach the initial mash temperature. Once the first temperature rest is complete, a portion of the grain and water is scooped or shoveled out of the mash tun and into the kettle or another heated vessel, where it is brought to a boil. The portion removed, which can often be as much as a third of the grist, is called the decoction.

The decoction may require stirring during heating to avoid scorching the grain; this adds some extra work during the mash. The decoction step also adds time to the mash, since unlike the infusion water in a step infusion mash, the water cannot be heated during a rest.

After boiling, the decoction is returned to the mash tun to achieve the next temperature rest.

[edit] Sample Decoction Mash Schedules

This section contains discussions of a number of sample schedules for decoction mashes, including single, double, and triple decoctions. The brewer should bear in mind that some mash schedules are better suited for use with modern, well-modified European malts than others.

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[edit] Single Decoction

Mash diagram single decoction.gif

In a single decoction mash only one decoction is used. This decoction can be used to reach any rest, but most commonly it is used to get to mash-out. This can be a simple enhancement of a single infusion or step mash.

The mash schedule shown above is well suited for European and continental lager malts. It features a short protein rest at the higher end of the temperature range for proteolytic activity, a single temperature saccrification rest and a decoction to get to mash-out. Calculate your strike water to aim for a protein rest between 53 and 55 *C (129 - 133 *F) at a mash consistency of about 2.5 l/kg (1.2 qts/lb). This will put emphasis on the protein degrading enzymes that produce the medium chained proteins which are good for head retention and mouth feel. The well-modified modern malts already have enough short proteins (amino acids) and a rest closer to 50 *C (122 *F) is not necessary. Dough-in and check the temperature. Plan on holding this temperature for 20 min. During this time bring about half of the amount of water, that was used for dough-in, to a boil. The pH of the mash should be checked and corrected if it is not within the 5.2 - 5.5 range. When the protein rest is over, use a heat resistant vessel to scoop the boiling water into the mash. This is best done by holding the thermometer in the mash with one hand and scooping the water or stirring with the other hand. It is important to stir the mash well to even out its temperature. Add water until the desired mash temp of 65 - 68 *C (148 - 155 *F) is reached. You will notice that the thinning mash makes stirring easier. The resulting mash will have a consistency of about 3.5 - 3.75 l/kg (1.8 qts/lb) which is great for German style beers. Hold this rest for 45 min.

Check for conversion. Calculate the amount of decoction necessary to get to the mash-out temperature of 74 - 76 *C (165 - 170 *F) and pull this decoction. In order to prevent scorching get good mix of liquid and grains. This decoction should be brought to a boil over the next 10 to 15 minutes. A gentle flame while keeping the pot covered will prevent scorching even without the need of constant stirring. When the decoction comes to a boil remove the lid (watch out for boil-overs) and let it boil for 10 - 30 min. Shorter for light worts and longer for darker worts.

[edit] Double Decoction

[edit] Classic Double Decoction

Mash diagram double decoction classic.gif

The classic version of the double decoction is a shortened triple decoction. It omits the acid rest and starts with the protein rest. Because of this only 2 deooctions are needed to get to mash-out. One to get from the protein rest to the saccrification rest and another one to get from the saccrification rest to mash-out. Like the triple decoction, this mash rests the main mash at the protein rest for a long time. With well modified lager malts, this may result in overly extensive protein degradation. The following two sections show mash schedules that avoid this problem.

[edit] Enhanced Double Decoction

Mash diagram double decoction enhanced.gif

This is a mash schedule that was taken from German brewing literaure [Narziss,2005]. The great thing about this mash is that it is almost as intensive as a triple decoction, when it comes to the amount of mash that is boiled, but a little bit shorter and without a long protein rest. The basic idea of this mash is to pull a decoction that is large enough to get the mash from acid rest directly to the saccrification rest. But when this decoction is returned to the main mash, it is returned in 2 parts: first to reach the protein rest and later to reach the saccrification rest. The second decoction is done to reach mash-out.

This mash starts like the triple decoction. Dough-in is done to reach the acid rest where the mash pH is corrected if necessary. Now a large decoction (about 50 - 60% of the mash) is pulled and heated. It is advisable to add some water 5-10% of the decoction volume to compensate for boil-off and thin it out a little. Due to the size of the decoction it should be rested for protein rest and must be rested for the saccrification rest. The saccrification rest is necessary to get the most out of the enzymes in this mash as they will be destroyed once the decoction is brought to a boil. This rest can be done at 155 - 162 *F (68 - 72 *C) where the conversion should only take 15 - 20 min. Taking the pot off the burner, closing it with a lid and wrapping it in blankets for insulation works very well. Check temperature and conversion after 15 min. When fully or almost converted, return the pot to the burner and start heating it gently again to bring it to a boil. Watch out for the foam-up of the decoction shortly after it comes to a boil.

The mash is now boiled from 10 - 30 min. After that a heat resistant vessel is used to scoop some of the decoction back into the main mash. Stir well and check the temperature of the main mash. Continue adding the decoction until the desired protein rest temperature is reached. After that the main mash is rested for 15 - 20 min while the rest of the decoction is still boiling. Once the protein rest is over, continue adding the decoction, stir and check temperature until the desired saccrification rest temperature is reached. Hopefully enough decoction was pulled to reach this rest. If some decoction is left over once the rest temperature is reached, let it cool and add it when its temperature is close to the temperature of the main mash.

Rest the mash for saccrification. Check for conversion and when the desired mash time rest time is up and conversion was achieved, pull the 2nd decoction. Heat it to boiling, boil for 5-20 min and return it to the main mash to reach mash-out.

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