THE ALCOHOL TEXTBOOK THE ALCOHOL TEXTBOOK

Managing the four Ts of cleaning and sanitizing 305
products of fermentation are easily removed with
water. Most compounds are more soluble in hot
water than cold, so heating water helps make it
a better cleaner. Exceptions are the water
hardness compounds, particularly those of
temporary hardness. These become less soluble
at higher temperature leading to the deposition
of calcium carbonate-based water scales. An
important consideration in the use of hot water
for cleaning is to prevent formation of scales by
softening the water. Many cleaners contain
water-softening ingredients.
Pure water has a relatively high surface
tension, as shown by the fact that water tends to
form round drops when placed on a surface.
Water is described as not being good at wetting
because the water forms droplets and does not
wet the entire surface. Compounds that
concentrate at the surface of water often decrease
the surface tension of water droplets, making it
easier for the water to spread out and cover more
of the surface. These compounds are called
wetting agents.
Alkali
An alkali is something that raises the pH of
water. The pH depends on the concentration of
hydroxide ions: the more hydroxide the higher
the pH. The most common alkali used for
cleaning is caustic soda (sodium hydroxide),
which is an excellent source of hydroxide ions
and is relatively inexpensive. Unfortunately,
caustic soda has poor rinsability; it does not
rinse away very easily after it is used for cleaning.
Potassium hydroxide is also a strong alkali and
it rinses more easily than sodium hydroxide, but
it is significantly more expensive. Addition of
surfactants to cleaning compounds with caustic
soda will improve rinsability.
Other alkaline compounds include silicates,
phosphates and carbonates. Sodium metasilicate
is a commonly used alkali. It provides a high
pH, although not as high as caustic. It tends to
keep removed soil in suspension, providing
good removal from the area cleaned. Silicate
does not tend to corrode soft metals such as
aluminum and copper, while caustic attacks
these metals. Silicates are also less dangerous to
handle.
Alkaline phosphates, especially trisodium
phosphate, provide significant alkalinity, but less
than caustic or silicates. It is safe for use in hand
cleaning applications. It helps to soften water
by forming an easily removed precipitate with
hardness compounds. It can be combined with
sodium hypochlorite to form a co-crystal, which
is a convenient, stable source of chlorine.
Sodium carbonate or washing soda is a mildly
alkaline compound that helps soften water as
well as provide alkalinity. Its main use is in a
mixture with solid caustic soda where its anticaking
activity helps prevent handling problems.
When alkaline compounds raise the pH level,
they increase the amount of negative hydroxide
ions present. This has two main effects. Bonds
between the amino acids of proteins can be
hydrolyzed or broken by reaction with
hydroxide. This makes the proteins smaller and
more soluble so that they can be removed. Acid
compounds can have their acidic hydrogen
removed by neutralization with hydroxide. The
compounds are converted to their negatively
charged ionic form. The negative ions repel each
other, leading to a breakup of large aggregates
of soil to smaller ones. This breakdown is called
peptizing. The negative ions are also more
soluble in water, leading to their removal from
the surface. Proteins, composed of amino acids,
are very effectively cleaned by alkali. If the alkali
is strong enough, carbohydrates can also be
converted into negative ions leading to their
easier removal.
Alkali will also break down fats and oils to
their component glycerol and free fatty acids.
This is the basis for making soap from fat and
alkali, and the process is called saponification.
Provided that hardness ions are not present to
precipitate them and that the high pH keeps the
fatty acids in the ionized form, fats and oils are
effectively removed by alkali.
Most inorganic scales are not effectively
removed by alkali.
Chelating agents and sequestrants
Chelation is the binding of ions, most
importantly the hardness ions calcium and
magnesium, so that the hardness does not cause
precipitation and scale formation. Common
chelating agents are EDTA (ethylene diamine
tetraacetic acid) and NTA (nitrilo triacetic acid).
Sequestrants, especially the polyphosphates,
have a similar action. Sodium gluconate acts as