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Analysis
with the TANNOMETER
| Example: Analysis of beer The following descriptions concerning the automatic modes relate to the
analysis of beer. They are written with the help of Prof. em. Lucien Chapon. There are,
however, analogue relations to other solutions. |
The equilibrium PT - Key to quality
| The concept according to which an
equilibrium occurs between proteins (P) and tannoids (T) P+T=PT allows us to understand
that a wort and the corresponding beer cannot simultaneously be rich in proteins and
tannoids. The control of these two classes of
components gives the brewer precise information about the quality of the raw materials
malt and hops.
The maltster uses the Tannometer for the purchase of
his barley and the control of his production.
At the different stages of beer production, rapid
analytical methods give the possibility, to follow the dissolving of tannoids, the
precipitation of the proteins and the efficiency of stabilisation treatment aimed either
at the tannoids or at the proteins.
This is a very simple way for optimising the amount of
stabilising agent needed.
Literatur |
| Conclusion The analysis encompasses both tannoids and proteins. Both are
particularly important for the chemical-physical stability. Additionally, reducing
substances which buffer the damaging dissolved oxygen can be determined. Likewise the
Alcohol chill haze test, which allows fast determination of the total turbidity building
substances, is of significant value. |
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1.
Tannoids
| The tannoids are defined as the fraction of
polyphenolic compounds which can be precipitated by polyvinylpyrrolidon (PVP). They
include the low and medium molecular polyphenols, the polymers of catechin and
anthocyanogens. Tannoids come from the malt and hops. Although present at relatively low
concentration, they play an important part in the colloidal and taste stability of beers.
On the one hand they can precipitate the sensitive proteins of the wort and beer, on the
other hand they act as protective agents. The tannoid content of beer, wort, barley, malt
and hop extracts can be determined by precipitation with PVP. This polymer which can be considered as a structural analog of proteins
binds with tannoids by hydrogen bonding to give an insoluble complex which leads to the
formation of a haze.
On continous injection of a solution of PVP into the
sample a haze develops until all the tannoids are bound. Beyond this point an excess of
PVP brings about a progressive dissolution of the haze.
The amount of PVP necessary to reach the maximum is
proportional to the tannoid content of the sample. The Tannometer measures the amount of
haze formed versus the amount of PVP injected and expresses the result in mg PVP/litre.
The curve and the result are printed by the inbuilt plotter.
(literature: Der Begriff Tannoide, Monatsschrift für
Brauwissenschaft, No. 7/8 93, page 263-279)
Literature |
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2.
Sensitive Proteins
| During the lagering of beers their tannoids condense
into true tannins. They are then capable of binding themselves with certain proteins to
give associations of low solubility. Such a process corresponds to the first step towards
the formation of permanent hazes. It proceeds at a very low speed, even at 40°C or 60°C,
for strongly stabilised beers. To simulate the spontaneous increase of the true tannin
concentration a solution of gallic tannin is injec-ted into the beer. The substances which
are protein like in nature and with the strongest affinity with the tannin are
in-solubilised first. They are known as “sensitive proteins”. (literature: Der Begriff Eiweißempfindlichkeit, Monats-schrift
für Brauwissenschaft, part 1 to 3, No. 9/10 95,
1/2 96, 3/4 96) further Literature |
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3. Reducing Power
| Reducing Substances
according to MEBAK by DPI,
(similar to ITT-Test)
Reducing Substances
according to Chapon by DPFe3-complex |
Beer contains important oxidisable components. The
oxidation of some of them impairs the colloidal stability of the beverages as well as its
organoleptic quality. The initial freshness gives way to an oxidised taste. Such a beer,
impaired by the oxygen in the air, loses its appeal to the consumer. Malt and hops give the beer protective substances endowed with
reducing capacity. They are mainly phenolic in nature, and of low molecular weight, but
also include melanoidins formed during the kilning process of the malt and the boiling of
the wort. They are able to slow down, if not prevent, oxidation harmful to the quality.
Since beers are exposed to adverse conditions during
transportation and storage which can affect their original quality, knowledge of their
reducing capacity is of great interest.
Direct determination of the reducing power is not
possible on account of the sluggish reactivity of the molecular oxygen. Nevertheless it is
possible to take advantage of the reactivity of the ferric dipyridyle complex (DPFe3,
according to Chapon) or that of the 2.6. Di-chlorphenolindophenol (DPI, according to
Hartong) toward the above reducing substances to determine the buffer-capacity of malt or
hop extracts and that of beers.
Practical experience has proved that the taste
stability of beers with a large reducing capacity was generally good. However there is no
reference value which could be taken into account when predicting the actual behaviour
towards oxygen.
Literature |
Reducing Substances acc. to
Mebak:
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Reducing Substances acc. to
Chapon:
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4. Chill Haze -
Alcohol-Chilling-Test (ACT)
| A beer sample cooled down below freezing point (downto
-8°C) develops a chill haze dependent on its condition. This haze is caused by
insolubility of polyphenol-protein complexes. The test carried out immediately after
filtration or bottling gives accurate information regarding the potential haze of the beer
and the efficency of the stabilisation treatment which can be adapted if required. During distribution and storage the ACT gives information
regarding haze forming condensation phenomena leading to an increase in tannin power
against haze sensitive proteins. This phenomenon, during which the molecular weight of the
tannoids increases, is caused mainly by oxidation to which beers poor in reducing
components are especially sensitive.
The addition of ethanol decreases the solubility of the
PT-complex and enhances the chill haze. In the ACT one can add upto 6% vol. ethanol. The
addition of 1% vol. alcohol has the same effect as lowering the temperature 1°C. The
Tannometer measures the chill haze as a function of temperature and time. The result
expresses the haze formed in EBC units after a preset time (40 minutes).
Literature |
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5. Ammonium Sulphate titration limit (Hartong)
| This rapid analytical method gives information about
the hydrophilie character of the colloidal constituents of beer. The addition of ammonium
sulphate to beer induces a haze formation. The
greater the amount necessary to achieve a given haze value the higher the chances of
stability. The limit of precipitation is expressed as the volume of saturated ammonium
sulphate solution which induces the beginning of the haze formation.
There is however no linear relationship between the
precipitation limit and the colloidal stability, since it depends not only on the proteins
but also on other factors such as tannin and oxygen content.
Literature |
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