Mashing

Starch conversion is the most important aspect of mashing. In barley starch makes up 63% - 65% of the dry weight. Starch is a polysaccarid (very large chains of glucose) which is insoluble in water. Brewer's yeast, however, can only ferment monosacharides (glucose, fructose, and galactose), disacharides (sucrose, lactose, and maltose) and trisacharides (maltotriose, nigerotriose, melezitose, etc). The latter can only be completely fermented by lager yeast strains (s. uvarum).

In order to convert the starch into water soluble sugars (fermentable and unfermentable), two processes need to happen Gelatinization and Enzymes Catalysis.

Gelatinization

Starch granules are insoluble in cold water and will absorb only little water. They form a suspension that quickly settles once agitation stops. As the water is heated (>50°C) more and more water is absorbed and the granules start to swell. The water absorbed during this process can be up to 30 times the weight of the starch granule. This uptake of water initially happens within the amorphous growth rings. At this point the granule starts to leach amylose and the crystalline layers break open and separate from the starch granule as gelatinous sheets. At this point the crystalline structure is lost and the process becomes irreversible with respect to the shape of the starch granule. The starch granule has gelatinized.

The starch is gelatenized to become water soluble.

For starch found in barley and malt the gelatinization happens above 140ºF (60ºC). Other starches (rice for example) gelatinizes only above 194ºF (90ºC) and requires boiling before it can be converted by enzymes.

Catalysis

Catalyzed reactions are typically used to accelerate the rate by which a specific chemistry proceeds. Essentially, the action of the catalyst is to provide an alternative, lower energy pathway for the reaction. The catalysts (in our case the enzymes) are not affected by the reaction as far as the chemical structure or mass at reaction completion. Catalysts are not consumed in the catalyzed reaction but can act repeatedly.

The activity of the amylase enzymes (catalysts) break the long chained starch molecules into shorter chains.

The starch found in malt is composed from the polisaccharides Amylose and Amylopectin:

• Amylose is a polysaccharide is a single chain of α-D-glucose units, bonded to each other through α(1→4) glycosidic bonds. It is one of the two components of starch, making up approximately 20-30%. Because of its tightly packed helical structure, amylose is more resistant to be broken by the enzymes than other starch molecules and is therefore an important form of resistant starch. The number of repeated glucose subunits (n) is usually in the range of 300 to 3000, but can be many thousands.

• Amylopectin is a water-soluble polysaccharide and highly branched polymer of α-glucose units found in plants. It is one of the two components of starch, the other being amylose. Glucose units are linked in a linear way with α(1→4) glycosidic bonds. Branching takes place with α(1→6) bonds occurring every 24 to 30 glucose units, resulting in a soluble molecule that can be quickly degraded as it has many end points onto which enzymes can attach. 76-83% of barley starch is Amylopectin.

Due to the malting process some enzymes are also found in the malt:

• Beta amylase, presented in the malt, produces Maltose, the main wort sugar, by splitting 2 glucose molecules from the non-reducing end of a glucose chain. It is therefore able to completely convert Amylose. But since it cannot get past the branch joins, Amylopectin cannot completely be converted by beta amylase. The optimal pH range for beta amylase between 5,4 and 5,6 and the optimal temperature range is between 140ºF (60ºC) and 150ºF (65ºC). Above 160ºF (70ºC) beta amylase is quickly deactivated. There is no point in lowering the temperature afterwards.

• Alpha Amylase, also present in the malt, is able to split 1-4 links within glucose chains. By doing so, it exposes additional non-reducing ends for the beta amylase. This allows for the further conversion of Amylopectin. The optimal pH range is between 5,6 and 5,8 and the optimal temperature range is between 162ºF (72ºC) and 167ºF (75ºC). Above 176ºF (80ºC) alpha amylase is quickly deactivated.

• Limit Dextrinase is able to split the 1-6 links that are found in Amylopectin. It is therefore able to reduce the amount of limit dextrins (glucose chains containing a 1-6 link) which are left over by alpha and beta amylase activity. Its optimal pH is 5,1 and the otimal temperature range is between 133ºF (55ºC) and 140ºF (60ºC). Above 149ºF (65ºC) this enzyme is quickly deactivated. Because of an optimal temperature well below the commonly used saccharification rest temperature for single temperature saccharification rests, this enzyme plays only a minor role in most mashing schedules. Extended rests in the range of 130ºF (50ºC) benefit a higer fermentability of the wort.

During mashing the starch conversion to fermentable and unfermentable sugars is mostly done though beta and alpha amylase activities.

After completed mashing the mash and the resulting wort needs to test negative with iodine (i.e. conversion has been completed). This is the case for linear dextrines shorter than 9 glucose molecules and branched dextrines with less than 60 glucose molecules.

The fermentability should match the targeted style of beer.

If a single temperature rest for starch conversion is chosen, it needs to allow for sufficient beta and alpha amylase actitiy. This is given at temperatures between 140ºF (60ºC) and 160ºF (70ºC), but only temperatures between 148ºF (65ºC) and 158ºF (69ºC) are commonly used. The higher the temperature the lower the limit of attenuation (fermentability) of the resulting wort will be.

The following table lists the relation between temperature and fermentability:

The rests were held until conversion was complete. It should also be noted that the exact fermentability will depend on more than the temperature. The fermentability is mainly determined by the time the beta amylase was active. The higher the temperatiure, the quicker the beta amylase is deactivated. This results in less maltose production.

While temperature has the biggest impact, the following factors also determine the achieved fermentability:

• pH - a given pH may favour one enzyme over the other

• time - A longer mash will give the enzymes more time to break down starch and dextrines

• water/grist ratio – With today’s well modified malts, the mash density has little impact on the fermentability of the produced wort.

• crush - a finer crush makes the starches accessible more quickly thus giving the beta amylase more time to work on their conversion before it is deactivated. The results is increased fermentability.

• mash-schedule. The chosen mash schedule has a very significant impact. Dough-in at temperatures well below the optimum for beta and alpha amylase allow the starches to be hydrated before the amylase enzymes are activated. Again, this gives the beta amylase more time to work on starch conversion, thus increasing the fermantability. Decoction mashing does the same, even better. The boiling of the mash gelatinizes the starch and makes it available immediately. This is important for the bata amylase because at its optimal temperature barley starch is just starting to gelatenize. Though this effect does increases the fermentability, the inactivation of enzymes during the mash depletes the number of available enzymes.

• enzymatic power of the mash - This heavily depends on the grist. If large amounts of highly kilned base malts (like Munich) or large amounts of adjuncts (which are unmalted grains that do not contain a significant amount of enzymes) are used, the mash will have a lower enzymatic strength. Thus less maltose is produced and the fermentability suffers. This needs to be counteracted with a lower rest temperature and/or a more intensive mashing schedule.

Brewers commonly apply a multi step saccharification rest to achieve better fermentability. As noted above, the gelatinization of barley starch happens between 140ºF (60ºC) and 150ºF (65ºC).

This means that at the optimal temperature for beta-amylase not all the starch may have gelatinized and is accessible to the enzymes. A multi step saccharification rest would employ a first rest between 140ºF (60ºC) and 150ºF (65ºC) which gives the beta amylase plenty of time to produce maltose from the accessible starches.

Due to the limit dextrinase and already existing alpha amylase activity, the 1-6 links of amylopectin don't pose a limit for the beta amylase. This rest is commonly known as maltase rest. The lower the temperature of this rest, the longer the beta amylase will last and the more maltose is produced which increases the fermentability.

Since the mash is generally not completely converted after the 30-60 min maltose rest, a second conversion rest, called saccharification or dextrinization rest is employed.

This rest is held between 160ºF (70ºC) and 164ºF (72ºC) which is well above the gelatinization temperatuere for barley starch and within the optimal temperature range for alpha Amylase which will quickly convert the remaining starches.

This rest is usually held until conversion of the mash is complete. Another benefit of this rest is the formation of foam positive glyco proteins.

If even better fermentability is desired, multiple rests within the beta and alpha amylase temperature range are possible. Such a mash schedule is used by Anheuser Bush to brew Bud Light without the use of enzyme additions in the mash.

In order to leave as little dextrines as possible, their saccharification "rest" takes 2 hours while they slowly step the mash from 140ºF (60ºC) to 160ºF (70ºC). Such a mash schedule could be used by home brewers to brew highly attenuated styles like Belgian Saisons.

General tips:

• There are temperatures and pH levels that favor the performance of one enzyme or another. Temperature being the determining factor of which enzyme will be predominant.

• The inactivation of all beer enzymes occurs after 80°C, so make sure that during the mash out the temperature does not exceed 78°C. Above that, there is a risk of extracting tannins from the malt skins , which will cause astringency to the beer.

• The pH (hydrogen potential) affects the structure of proteins, each one has its "own" optimum pH for maximum activity. There is conversion of starch with a different pH than indicated, however, it is less than it could be and it isn't ideal. When added to the boiler the malt naturally lowers the pH of the water. However, each brewer must know the pH of the water, so that it can stay within the appropriate parameters for a good mash. Generally speaking, if the pH of the water is between 6 and 7, after adding the malt and waiting for 5 to 10 minutes, the pH of the mash should be between 5 and 6. The pH range of the brewing water most desired for making beer is between 5,2 and 5,4.

• Following the recipe, respecting the indicated temperature (s) and keeping the pH range between 5,2 and 5,6 is the best way to keep the enzymes working the way we want.

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• One point about temperatures that doesn't have much to do with enzymes is that a stop of at least 15 minutes at 60°C helps to solubilize the starch and enzymes in the wort. That is, even if you want a beer with more body and less attenuated, a short stop at 60°C also helps a lot to increase the conversion efficiency.