Mashing procedures

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This article tries to explain the various mashing procedures that are of interest to the home brewer. Mashing procedures are basically the application of the The Theory of Mashing by mixing the grain with water (mash) and resting this mash at a single or multiple temperatures to activate enzymatic activity which converts the grain solids into wort soluble compounds.

Which mash schedule to choose

This question comes up quite frequently in the form of "What benefit do I get from using a more complicated mash schedule than single temperature infusion?".

Mashing needs to be seen as an extension of the malting process and what wasn't done during the malting of the grain, needs to be done during mashing. And the more modified a malt is, the less mashing steps are necessary to produce a wort suitable for brewing a quality beer. Even worse, by selecting a more intense mashing schedule for a highly modified malt certain steps, like protein conversion, can be overdone and lead to a less optimal wort composition.

Here is a list of some malts showing mashing schedules that work well for them:

  • American or British 2-row (Pale malts): single infusion mash
  • Durst TurboPils: single infusion mash
  • Durst Pilsner: single infusion or 2 step infusion
  • Briess Pilsen: 2 step infusion / decoction mash
  • Weyermann Pilsner/Vienna/Munich: 2 step infusion
  • home malted malt: multi step infusion / deoction mash

Single temperature infusion mash

Mash diagram single infusion.gif

The single infusion mash uses a single temperature rest at which the beta and alpha amylase enzymes are active to convert the malt starches into wort sugars. The higher the mash temperature is, the lower the limit of attenuation of the resulting wort will be. This is the most common mash schedule among home brewers and craft brewers because it is well suited for American and British 2-row malts which are generally highly modified and don't benefit from a lower temperature rests. It is also well suited for the use of unheated mash tuns (e.g. coolers) which are the preferred mash vessel among most home brewers. The rest temperatures are commonly between 149 *F (65 *C) and 165 *F (69 *C). Many brewers like to use 154 *F (67.5*C) as their preferred mash temp as it gives a nice balance of body and fermentability that works well for British and American style ales.

In order to do a single infusion mash, the strike water (water used for the mash) is heated to a certain temperature such that when the grains are mixed in, the resulting temperature is the desired rest temperature. The temperature of the strike water can be calculated with the following formula [Palmer, 2006]:

Strike Water Temperature Tw = (.2/R)(T2 - T1) + T2

  • R = Ratio of water to grain in quarts per pound
  • T1 = the temperature of the grains in Fahrenheit (or Celsius)
  • T2 = the target temperature of the mash in Fahrenheit (or Celsius)
Note: Plamer writes that R can be expressed as quarts per pound or litres per kilogram. This is not correct since 1 l/kg is approximately 0.5 qt/lb. This needs to be accounted for when using metric units in the above formula. The temperature however can be used as Fahrenheit or Celsius as long as all temperature values use the same unit or measure.

Hitting the mash temperature is for many brewers their biggest problem when doing a single infusion mash. This can some times lead to frustration. The reason for that is, that the above formula doesn't account for heat loss to the mash tun. It basically assumes that the mash tun has a thermal capacity of 0. To get around this one can preheat the mash tun with some boiling water or adjust the strike water temperature based on the results in previous mashes. If the latter is used the brewer should keep the mash tun and grain temperature constant between the different mashes. Another way to elimitate the unknown factor of the mash tun's thermal mass is to ajust the strike water's temperature after it has been added to the mash tun and before the grains are added. This can be done with hot and cold water.

When mashing in at or above the gelatinization temperature of barley starch (between 140 and 150 *F / 60-65 *C) the grains should always be added to the strike water rather than the strike water to the grains. This minimizes the formation of dough balls. Such dough balls form when the starch around them gelatenizes which provides a barrier for mash water. If they are not broken up during dough in, they can later release unconverted starches into the mash.

With today's highly modified and thus enzymatic strong malts, the mash is generally converted after 15-30 min based on the rest temperature. Lower temperatures mashes convert slower than higher temp mashes of the same grist (see The Theory of Mashing for further details). Most brewers do however mash 60-90 minutes to ensure complete conversion and for the time it gives them to heat the sparge water for example. It is always a good practice to check for conversion of the mash with an iodine test.

To do an iodine test you need a white plate, small spoon and iodine/starch test solution (some home brew stores sell iodine test strips, but they are for testing an iodine solution not for testing for starch). Stir the mash a part ofd the mash a little and take a small sample onto the plate with the spoon. Now drip a few drops of iodine solutions onto that sample. If there are still unconverted starches in the mash, the sample will turn black or dark purple. The mash is converted when you don't see that happening. At this point the wort should also taste sweet. Discard the sample as iodine is toxic.

Though this is considered a single temperature step mash, a mash-out rest can be added. Using hot water infusions (or even decoction as shown later) the mash temperature is raised to 167 *F (75 *C). No harm is done if that temperature is not reached exactly. It should however not be exceeded. Many brewers believe that the purpose of this rest is to stop the enzymatic activity, but that is usually not the case as the alpha amylase is not fully deactivated until 176 *F (80 *C). The prupose of the mash-out is to aid lautering as hotter wort will flow more easily while still allowing enzymatic activity to convert any starches that might be unlocked during lautering [Narziss, 2005]. While this is of a lesser concern for the homebrewer, a mash-out is still a good practice.

Multi step infusion mashes

Multi step infusion mashes refer to mashes with more than one temperature rest not counting the mash-out rest. From one step to the next the temperature is generally increased by the use of heat (direct or indiect), hot water infusions or both. There are various mash rests that can be of interest for the brewer:

  • acid rest: for enzymatic mash acidification and no-rush mash pH treatment. Since no significant conversion processes take place at this temperature there is no concern having the mash rest at this temperature for an extended amount of time.
  • ferulic acid rest: This is a little different from the regular acid rest as this rest is primarily for the generation of ferulic acid which wheat beer yeasts convert to 4VG, the phenolic character of Bavarian Wheat beers.
  • protein rest: This is actually the first additional mash rest that comes to mind when multi step mashes are discussed. The temperature and extend of this rest depends on the degree of modification of the malt. Rest temperatures closer to 122 *F (50 *F) emphazize the generation of short length proteins (amino acids) and temperatures closer to 133 *F (55 *C) result in more medium chained proteins (good for head retention and body). Well modified modern malts, which already have higher levels of amino acids, benefit from a protein rest closer to 133*F (55 *C)
  • saccrification rest: This can be done as a single saccrification rest like it is used for single infusion mashes or multiple rests which emphazise beta and alpha amylase speraratly. The latter can result in better fermentability of the wort since it tries to get the most out of the beta amylase.

When direct heat is used to increase the mash temperature between the rests, the temperature should only rise 2-4 *F (1-2 *C) per minute.

The following is an example of a 2 step infusion mash that works well with moderately well modified German malts:

Mash diagram 2 step infusion.gif

It employs a short protein rest at 133 *F (55*C) and a single saccrification rest. The temperature is increased by the use of boiling water. To run as mash schedule like this, calculate the strike water temperature for your grain, a grist/water ratio of 1.25 qts/lb (~2.5 L/kg) and a rest temperature of 129-133 *F (53-55 *F). Add the water to the grain. Since the dough in happens below the gelattinization temperature of barley starch it is safe to add the water to the grain since there won't be any dough balls. There is also nothing wrong with adding the grain to the water, but it might be convienient to mill the grain directly into the mash tun. The temperature should stabilize somewhere between 122 and 133 *F (50-55 *C). If it is to close to 50, don't worry, just shorten the length of the protein rest or add some boiling water to raise the mash temp closer to 55*F. This assumes that you use fairly well modified (not overmodified) modern lager malts. Use this rest to measure and adjust the pH of the mash if you are set up to do that. The later addition of more water will not have any significant affect on this pH. While the mash is resting at the protein rest bring about 60-70% of the amount of water that you used as strike water to a boil. When the protein rest is over use a heat resistant vessel to soop some boiling water into the mash and stir to mix it in well. Measure the temperature and repeat the process untill you hit the desired saccrification rest temp. This rest temp will depend on the desired attenuation of the wort and you will have to find the optimal temperature by experimenting. As a start you can use the temp that you would use for a single infusion mash. But due to the lower temperaure rest and limited beta amylase and limit dextrinase activity during that rest, the resulting wort fermentability will be higher compared to a single infusion mash at the same saccrification rest temperature.

You could also use this formula to calculate the amount of water that needs to be added to raise the mash temperature [Palmer, 2006]:

Wa = (T2 - T1)(0.2G + Wm)/(Tw - T2)

  • Wa = The amount of infusion water added
  • Wm = The total amount of water in the mash
  • T1 = The initial mash temperature
  • T2 = The target mash temperature
  • Tw = the actual temperature of the infusion water
  • G = The amount of grain in the mash

But the addition of boiling water until the new rest temp is reached is more reliable as it can account for factors that the above formula can't. And since the resulting mash will be quite thin, stiring it and getting the heat evenly distributed for a reliable mash temp reading is not as difficult as it is in a ticker single infusion mash.

Some brewers are concerned that a thinner mash leads to more tannin extraction, but quite the opposite is true. German brewers prefer thinner mashes for delicate and lighter colored beers as it will prduce more of the desirable first wort and since less sparge water has to be used, less tannins are extracted during lautering. This however is only a concern for fly sparing.

The enzymatic activity also benefits from the changing mash thickness. A thicker mash during the protein rest enhances the protoelytic activity and a tinner mash during the saccrification rest enhances the amylase activity.

If there is room left in the mash tun, mash-out can also be reached though another infusion with boiling water or through a decoction. But that will be covered later.

Decoction mashing

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 orginates from a time when malt quality was not consistent and temperatures could not be measured. The long boiling of the grain make the starches more accessible for the enzymes. This is particularly important for undermodified malt where the cell wall are not as broken down as they are in well modified or overmodified malt. The boiling of a defined portion of the mash and returning it to the main mash to raise the temperature als helped the consistency in mashing before thermometers were available.

Today even the european malts are generally well modified and can be used 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 mash 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. This section showes a number of decoction mashing schemes. Some of them are especially well suited for the use with modern well modified european malts.

Tripple Decoction

Mash diagram tripple decoction.gif

The tripple deoction is the grand father of all deoction mashes. This is how the first Pilsners were brewed in Pilzen and how many traditional German breweries brew their dark beers (Munich Dunkel, Bock, Doppelbock) to this day.

The tripple decoction mash employs 3 main mash rests: acid rest, protein rest and saccrification rest. from each of these rests a dectcoction is used to reach the next rest until the mash-out is reached. The acid rest is a convinient rest to do mash pH adjustments. Not only does it serve to lower the pH by simply resting at this temperature, but since there is no enzymatic activity that can have a detrimental affect on the final result, there is no rush to move to the next rest.

There are several formulas out there for calculating the decoction volume. Some of them are simple and others try to account for factors such as the heat capacity of the grains and the mash-tun. The easiest way however is to estimate the decoction volume with a simple formula like this:

deoction volume = total mash volume * (target temp - start temp) / (boil temp - start temp)

and add about 15 - 20%. The idea is to deoct more mash than necessary. When the decoction is added back to the main mash, it is not all added at once. Instead it is added in steps while the actual temperature of the mash is constantly checked which requires a thorough mixing of the mash after each addition. Once the target temperature is reached the remaining decoction is left to cool and added once its temperature is close to the mash temperature. By doing so one can account for additional factors that affect the actual needed decoction volume such as: evaporation during the boil, temperatire drop in the main mash and others.

The tickness of the decoction depends on the tickness of the main mash. Though it is preferred to leave a lot of the liquid back in the mash tun, the decoction should not be to thick (grain still being submerged in liquid) to make stirring it easier and keep it from scorching easily. If the main mash can be kept at the preferred thickness of 1.5 - 2 qts/lb (3-4 kg/l) the decotion should have a tickness of 1-1.25 qts/lb (2-2.5 kg/l) this is about the tickness of a standard single infusion mash. At this tickness and with gentle heating, only little stirring is necessary to keep the mash from scorching.

All the decocion schedules provided here assume a deoction rise temp of 2-4 *F/min (1-2 *C/min). This is what is generally recommended in the literature for heating the deoction. There is also a saccrification rest at 155 - 162 *F (68 - 72 *C). The purpose of this rest is to untilize the enzymatic power of the decoction before its enzymes are destroyed by further heating. This is particularily important when brewing beers with a large percentage of the enzymatic weaker dark base malts. This rest doesn't have to be held at the main saccrification temperature. It is sufficient to rest in the alpha amylase range where the conversion is also done much qicker. After the decoction is converted or almost converted (iodine test) the heating of the mash is resumed.

The decoction is then boiled for 10 - 40 minutes. Shorter boil times for light colored beers, longer boil times for dark colored beers. If only gentle heat is applied during the boil, stirring should only be necessary occationally. Similar to wort boiling, excessive thermal loading of the decoction can result in a burnt flavor of the beer. If the deoction is boiled for an extended amount of time evaporation losses can be compensated with the addition of water (which can also be added after the decoction has been pulled, where it helps in tinning it out and makes it more managable) or larger deoction volumes.

Once the decoction is then added to the main mash to reach the protein rest. The temperature and time before pulling the next decoction should be based on the malt that is used. Less modified malts benefit from a rest closer to 122 *F (50 *C) which produces more amino acids, which is an essential yeast nutrient. In undermodified malts the protein conversion has not been diven far enough to allow for sufficient wort FAN (free amino nitrogen) without the use of a more intensive protein rest. If the malt is a well modified modern continental malt, the protein rest temperature should be kept closer to 133 *F (55 *C) and the next decoction should be pulled 5 - 10 minutes after the rest temperature has been reached. This serves to protect more of the medium chained proteins that are important for body and head retention. Or a decoction that allows for a shorter protein rest, which will be described later, should be employed

Again a decoction is pulled, rested for conversion and then brought to a boil. This time to reach the saccrificaton rest temperature. This temperature is similar to the saccrification rest temperature that is used for a single infustion mash, but the same temperature that was used in a single infusion mash may not give the same fermentability in a decoction mash. Boiling has destroyed more of the enzymes while it has made the starch also more easily accessible. The former would lead to a less fermentable result while the latter would shift the fermentability towards a more fermentable wort. This is only to illustrate that fine tuning of the saccrification rest temperature might be necessary for the optimal result. The saccrification rest temperature that would have been used in a single infusion mash is however a good starting point.


Mash diagram single decoction.gif Mash diagram double decoction classic.gif Mash diagram double decoction enhanced.gif Mash diagram double decoction hochkurz.gif

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