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11. Methods in use in the brewing industry to
reduce or control microbial contamination
Chlorine: this should not be used for water that goes into the
beer. Compounds which act as a source of chlorine either
directly as in chlorination, or indirectly through hypochlorite,
can produce phenolic taints in beer and highly volatile
halogenated hydrocarbons such as trihalomethanes (THM).
Chlorinated town water supplies require treatment before use.
-Chlorine dioxide functions as an oxidising agent. As a gas in
water it does not release halogens which could react to produce
taints. Chlorine dioxide is used at maximum level 0.5 ppm,
which is its maximum permitted level in potable water, and is
used to treat final rinse water after disinfection.
- Ozone: this treatment has a strongly oxidising effect which
kills micro-organisms.
- UV treatment: UV light in the wavelength of 200 to 280 nm
destroys the DNA in micro-organisms, provided the correct
doze rate is applied. Unlike chemical treatment, it has no
residual action and is limited to the point of application and
therefore the water should be treated immediately before use.
However, to be effective the water must be colourless and free
from suspended material or the sterilisation will be ineffective.
- Sterile filtration: physical water treatment, such as reverse
osmosis and distillation, will produce a sterile product.
Distribution through water mains and when using other water
treatments can result in micro-organisms being present in the
dilution and cleaning waters. Disinfectant and sterilisation is
often applied to final rise waters and critical dilution water such
as those supplying a culture plant or for post filter dilution.
Sterile filtration through a 0.2 micron filter (in practice 0.45
micron may also be used) to produce a sterile water at point of
use. (1500)
12. Breakfast Cereals
Most oats that are consumed directly as food are served as
breakfast cereal. Of the type that must be cooked, the most
popular by far is rolled oats. The process used to make rolled
oats is given in Fig. 1. The cleaned oats are treated with dry
steam at 100°C. This reduces the moisture content to about 6%
and inactivates enzymes, particularly the lipase system. Oats are
high in lipid and very susceptible to rancidity. Drying the hulls
makes them more brittle and therefore easier to remove.
The next step is to separate the hulls from the groats and the
whole oats that were not dehulled in the process. In general,
removing the hulls is not difficult; they are light and can be
separated by aspiration. It is much more difficult to make a
clean separation of groats from whole oats. Even a small
percentage of whole oats remaining with the groats is
unacceptable. Hulls in rolled oats are not palatable.
The groats are then rolled, or flattened, with large, very heavy
rolls to give the rolled product. Flaked whole groats take 10-15
min to cook. The cooking time (i.e., the time required for the hot
water to penetrate to the center of the flake) is determined by the
thickness of the flake. Of course, the cooking time is controlled
by the thickest point, and therefore a uniform piece is desirable.
To obtain rolled oats that cook more quickly, one must produce
a thinner flake. This is accomplished by cutting the groats into
two or three pieces before flaking. The smaller pieces give a
thinner flake that cooks faster (3-5 min), although the cooked
cereal will not retain its quality if held under hot conditions such
as on a steam table (the product becomes a gruel). Thus, we
have the classic trade-off between cooking time and product
11. Methods in use in the brewing industry to
reduce or control microbial contamination
12. Breakfast Cereals
Chlorine: this should not be used for water that goes into the
beer. Compounds which act as a source of chlorine either Most oats that are consumed directly as food are served as
directly as in chlorination, or indirectly through hypochlorite, breakfast cereal. Of the type that must be cooked, the most
can produce phenolic taints in beer and highly volatile popular by far is rolled oats. The process used to make rolled
halogenated hydrocarbons such as trihalomethanes (THM). oats is given in Fig. 1. The cleaned oats are treated with dry
Chlorinated town water supplies require treatment before use. steam at 100°C. This reduces the moisture content to about 6%
and inactivates enzymes, particularly the lipase system. Oats are
-Chlorine dioxide functions as an oxidising agent. As a gas in high in lipid and very susceptible to rancidity. Drying the hulls
water it does not release halogens which could react to produce makes them more brittle and therefore easier to remove.
taints. Chlorine dioxide is used at maximum level 0.5 ppm,
which is its maximum permitted level in potable water, and is The next step is to separate the hulls from the groats and the
used to treat final rinse water after disinfection. whole oats that were not dehulled in the process. In general,
- Ozone: this treatment has a strongly oxidising effect which removing the hulls is not difficult; they are light and can be
kills micro-organisms. separated by aspiration. It is much more difficult to make a
- UV treatment: UV light in the wavelength of 200 to 280 nm clean separation of groats from whole oats. Even a small
destroys the DNA in micro-organisms, provided the correct percentage of whole oats remaining with the groats is
doze rate is applied. Unlike chemical treatment, it has no unacceptable. Hulls in rolled oats are not palatable.
residual action and is limited to the point of application and
therefore the water should be treated immediately before use. The groats are then rolled, or flattened, with large, very heavy
However, to be effective the water must be colourless and free rolls to give the rolled product. Flaked whole groats take 10-15
from suspended material or the sterilisation will be ineffective. min to cook. The cooking time (i.e., the time required for the hot
- Sterile filtration: physical water treatment, such as reverse water to penetrate to the center of the flake) is determined by the
osmosis and distillation, will produce a sterile product. thickness of the flake. Of course, the cooking time is controlled
Distribution through water mains and when using other water by the thickest point, and therefore a uniform piece is desirable.
treatments can result in micro-organisms being present in the To obtain rolled oats that cook more quickly, one must produce
dilution and cleaning waters. Disinfectant and sterilisation is a thinner flake. This is accomplished by cutting the groats into
often applied to final rise waters and critical dilution water such two or three pieces before flaking. The smaller pieces give a
as those supplying a culture plant or for post filter dilution. thinner flake that cooks faster (3-5 min), although the cooked
Sterile filtration through a 0.2 micron filter (in practice 0.45 cereal will not retain its quality if held under hot conditions such
micron may also be used) to produce a sterile water at point of as on a steam table (the product becomes a gruel). Thus, we
use. (1500) have the classic trade-off between cooking time and product
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