Chemistry Reference
In-Depth Information
The diastatic power of malt is an expression of the amount and balance of the four
amylolytic enzymes produced during germination:
1. α-Amylase which solubilizes the starch polymers and releases extract.
2. β-Amylase which releases maltose and increases wort fermentability.
3. Limit dextrinase which debranches amylopectin and increases wort fermentability.
4. α-Glucosidase which releases glucose and aids wort fermentability.
Gelatinization
After completion of the proteolytic stage, the mash is raised to a higher temperature by
decoction mashing or by programmed infusion mashing. At this point, three very important
processes take place, gelatinization, liquefaction and saccharification. The gelatinization
temperature of starch is influenced not only by the type of starch (Table 8.9) but also by the
size and structure of its starch granules. As was previously mentioned, barley starch granules
are reported to be of two different granular sizes. The large and smaller granules are referred
to as A- and B-type granules, respectively. It is also well reported that the smaller the starch
granules, the higher their temperature of gelatinization. The reported negative impacts of
small starch granules are that, due to higher temperatures of gelatinization, they are less
digestible during mashing. In addition, they can impede wort filtration by cross-linking with
other polymers. In most cases, raw unmalted barley has higher levels of small starch granules
than malted barley since, during the malting process, the small granules are preferentially
degraded. In addition, at higher unmalted barley levels a greater proportion of smaller milled
grain components are present for mashing.
Liquefaction/saccharification
The next stage is liquefaction/saccharification. Liquefaction refers to the liquefying capacity
of the α-amylase and saccharification refers to the enzymatic production of fermentable
sugars. Prior to this stand, the starch in the mash remains ungelatinized, so it is not readily
available to be hydrolyzed by enzymes. The starch of barley malt gelatinizes at 61-65
◦
C. Once
gelatinized, the starch is digested rapidly by the α- and β-amylases present in the malt. Their
combined activities result in the production of large quantities of fermentable sugar, especially
maltose. α-Amylase randomly hydrolyzes starch to dextrins while β-amylase attacks the
starch and dextrins from the non-reducing ends, stripping off pairs of glucose molecules
(maltose). The saccharification stage seldom lasts longer than 30 min. At temperatures above
60
◦
C, which are required to obtain gelatinization of malt, the malt amylases, especially
β-amylase, are not very stable. During saccharification at 65
◦
C, β-amylase is inactivated
almost completely within 30 min. α-Amylase is also inactivated significantly, but some
residual enzyme activity is still present at the end of saccharification. The saccharification
stage therefore represents a compromise between the need for higher temperatures to obtain
gelatinization and lower temperatures to preserve enzyme activity. The chosen temperature
results in optimal sugar formation but incomplete starch degradation. Starch degradation
must be completed by raising the mash temperature again so that the finishing temperature
is at least 70
◦
C but below 80
◦
C. Smaller or larger proportions of fermentable sugars will be
formed in the wort, giving beers with different ratios of alcohol to non-fermented dextrins.
8.3.2.5
Mashing programmes
During mashing, the milled grain is mixed batchwise with water at different temperatures
for different times. This is referred to by the brewer as a mashing programme. The following
is an outline of a typical mashing programme used by a brewery using 100% malted barley.
