Giáo Trình Phân Tích Chuẩn Độ Điện Thế Winepac_E.pdf

Buch e indb 1 Wine Potentiometric Analysis Collection WINE PAC 6 6043 003 Methods for the titrimetric / potentiometric analysis of wine [ Dear Users, You have purchased a Metrohm titrator which, with[.]

cus-is made easier.

In the Application File you will find the descriptions of the corresponding analytical methods,

together with all the necessary remarks and explanations and – very important for you – outs of the instrument parameters and examples of curves.

print-All these methods are loaded on the Method Memory Card You only need to «feed» the titrator

with the card, load the required method into the working memory and off you go!!!

You are the specialists in wine production and have to ensure the outstanding quality of this wonderful drink when it is sold to your customers Although we at Metrohm do not understand much about your profession, we have been ion analysis specialists for many years The combi- nation of these two elements – and we are convinced of this – will produce optimal results.

For Titrando users: A conversion program ensures that you can adopt the Titrino parameters

in your Titrando without any problems This conversion program is contained in the PC Control program.

We wish you pleasure and success in your work,

Your Metrohm

8.110.1793

The supplied method memory card can be used with the following Titrinos: 798, 799, 785 and 751 (from program version 20) With VESUV 3.0 Light, which is also supplied (VESUV = Verification Support for Valida-tion), either you or your Metrohm agency can also transfer the parameter sets to the following Titrinos: 716,

736, 794 or 751 (<program version 20)

Among other things, the supplied CDs contain:

• The VESUV backup file, which allows you to copy the 25 methods into the 716, 736, 751, 785, 794, 798 and 799 Titrinos For further information please read the Section «Recreating methods» in the VESUV In-structions for Use, which is also supplied, or contact your local Metrohm agency If, instead of the printer, the VESUV software is used for adopting the data, then the «curve» report must be deleted at the Titrino, which must be set to «mplist» instead (VESUV can only process measuring point lists)

• A conversion program (converter) for adopting the Titrino parameters in the Titrando is contained in the 6.6050.000 PC Control program

• Acrobat Reader to be installed on your PC so that you can read PDF files

• Application Bulletins No 82, 83, 125, 129, 130, 133, 140 and 225

We recommend that you only load the methods that you require into your instrument

The method overview can be removed and stored together with the Wine PAC card and the appropriate instrument

Important symbols used in the methods

c(X) molar concentration of substance X in mol/L

M(X) molar mass of substance X in g/mol

w(X) mass fraction of substance X, e.g w(ethanol) = 13.5%

ρ(X) mass concentration of substance X, e.g ρ(NaCl) = 10 g/L

RSA South Africa

SA South America (Chile)

USA United States of America

C Free sulfurous acid (Free SO2)

C 1 Preparation and titer determination of the titrant

C 2 Orienting Ripper method (CH, SA, USA)

C 3 Official reference method (Au, EU, Israel, RSA)

D Total sulfurous acid (Total SO2)

D 1 Orienting Ripper method (SA, USA)

D 2 Official reference method (Au, CH, EU, Israel, RSA, SA)

E Volatile acids

F Fixed acidity

G Ascorbic acid (vitamin C)

H Reducing sugars

H 1 Preparing the solutions and determining the calibration factors

H 2 Determining the content of reducing sugars

J Carbon dioxide (CO2)

K Ash and ash alkalinity

L Calcium and magnesium

Techniques for chemical analysis and quality control during winemaking (2000)

Patrick Iland Wine Promotion, Campbelltown, South Australia 5074

ISBN 0646-38435-X

– Edmundo Bordeu S., Juan Scarpa B-B

Análisis químico del vino

Ediciones Universidad Católica de Chile (1998)

ISBN 956-14-0516-4

– Vorschriften zur Weinanalytik Bundesamt für Weinbau, Eisenstadt (Austria)

– Jornal Oficial das Comunidades Europeias, Portugal

– Gazzetta Ufficiale della Repubblica Italiana, 2a Serie speciale N 90 (1990)

– The Israeli Standard for Wine Determination, No 1318

– Schweizerisches Lebensmittelbuch, Kapitel 30 + 30A, Wein aus Trauben

– Jakob, L

Taschenbuch der Kellerwirtschaft

Fachverlag Dr Fraund GmbH, Wiesbaden (Germany) 1984

– West, S.J., Frant, M.S., Anderson, M.G., Chandler, L.L

A simple, accurate method for determining alcohol in wine using a fluoride ion-selective electrodeThermo Orion (1999)

• Metrohm buffer solution pH = 4.00 (6.2307.100)

• Metrohm buffer solution pH = 7.00 (6.2307.110)

• DIN buffer solution pH = 6.865 at 25 °C (6.881 at 20 °C) 0.025 mol/L each of

KH2PO4 and Na2HPO4, e.g Fluka no 82557 or Merck no 107202

• Buffer solution pH = 3.556 at 25 °C (3.57 at 20 °C) Saturated solution of potassium hydrogen tartrate in dist H2O This solution is not commercially available 1 2 g KHC4H4O6 and approx 0.1 g thymol are placed in a 200 mL volumetric flask and dissolved in approx 150 mL dist H2O under gentle heat-ing to approx 40 50 °C After cooling down the solution is made up to the mark with dist H2O and mixed This (preserved) buffer solution has a shelf life of approx 2 months

The pH value is defined as the negative logarithm of the concentration of free,

dissociated hydrogen ions in mol/L: pH = –log[H + ]

The pH scale ranges from 0 to.14 and the neutral point is at pH = 7.0, where H+- und OH– ions are present in equilibrium pH values <7 result from an excess of

H+, pH values >7 from an excess of OH– The more acidic a solution, the lower its pH; the more alkaline a solution, the higher its pH

Weak acids, e.g tartaric acid, do not dissociate completely, i.e only a small fraction (2 3%) of the H+ ions are released:

General

This also means that only on very rare occasions can the concentration of acids

or alkalis be inferred from the pH value

As the pH scale is logarithmic, this also means that small differences in pH respond to large differences in the H+ concentrations For example, at pH = 3.0 there are ten times as many H+ ions present than at pH = 4.0, and at pH = 3.1 there are twice as many H+ ions present that at pH = 3.4 The pH is measured potentiometrically – i.e by currentless potential measurements Apart from the measuring instrument (pH meter or titrator), a pH glass electrode and a refer-ence electrode are required For practical reasons these two electrodes are usually contained in a single combined electrode

cor-According to Nernst (we will not go into any details here) the theoretical slope

of such electrodes is 59.2 mV / pH at 25 °C or 58.2 mV / pH at 20 °C The trode zero point (0 mV) normally lies at pH = 7.0, but can vary within certain limits without the measuring accuracy being affected This variation called pH as

elec-(asymmetry) should not exceed ±0.25 pH units As a result of aging processes

the electrode slope diminishes with time If it becomes lower than 92% of the theoretical slope, i.e 54.5 mV / pH at 25 °C or 53.5 mV / pH at 20 °C then the electrode must be regenerated (send it to your local Metrohm agency)

«mV against pH»:

- Theoretical values

0 mV at pH = 7.00 and T = 25 °C Slope = 59.2 mV / pH (100%) +177.6 mV at pH = 4.00 and +414.4 mV at pH = 0.00 –177.6 mV at pH = 10.00 and –414.4 mV at pH = 14.00

- Example with practical values

0 mV at pH = 6.85 and T = 25 °C (–8.9 mV at pH = 7.00) Slope = 56.3 mV / pH (95.1%) +160.0 mV at pH = 4.00 and +385.2 mV at pH = 0.00 –177.8 mV at pH = 10.00 and –403.0 mV at pH = 14.00

The asymmetry potential

is determined by using

the buffer solution pH = 7.00; a second buffer solution is used to determine the slope of the pH electrode It is important that at least one buffer value is located close to that expected for the sample From the asymmetry potential and slope the pH meter determines the calibration line for the pH electrode and uses it to convert the measured mV values into pH values

returned to the bottle!

We recommend the use of a pH electrode with built-in temperature sensor – 6.0258.000 Unitrode

A) According to Au/CH/

RSA/SA (two-point

cali-bration)

Connect the electrode to

the Titrino, rinse it with

dist H2O and dab it dry

with a soft paper tissue

Immerse the electrode

in the first Metrohm

buffer solution, switch

on the stirrer, select

<CAL> mode and press

<START> Enter the set

value of the first buffer

solution, e.g 7.00 at 25

°C (7.02 at 20 °C) and

accept the value with

<ENTER> The buffer

is measured Rinse the

electrode with dist H2O,

dab it dry, immerse it in

the second buffer

solu-tion, stir, enter the set

value for the second

buf-fer solution, e.g 4.00 at

25 °C (3.99 at 20 °C) and

accept the value with

<ENTER> The second

buffer solution is

mea-sured Exit the calibration

mode with <STOP>

The calibration data can

be viewed with <CAL:

DATA> The key

CALDATE BUFFER BUFFER CAL4EMP

SLOPEREL



DATE CAL

PARAMETERS

CALIBRATION

STATISTICS

°C (6.881 at 20 °C) and the buffer solution pH = 3.557 at 25 °C (3.57 at 20

= 7.00 to 0 mV cally

electrode is stored in the electrolyte solution c(KCl) = 3 mol/L.

The pH value is of great importance for biological systems In wines it plays

a larger role than the titratable total acidity The pH influences the growth of microorganisms, the color and shade, taste, redox potential, the ratio of free to bound SO2, the stability, the possibility of forming or preventing iron phosphate turbidity, etc There is no direct relationship between the pH value and the content of titratable total acidity; in contrast, there is an (empirical) relationship between the pH value and the potassium hydrogen tartrate / tartaric acid ratio.The pH of a solution (wine) is also temperature-dependent This temperature dependency cannot be compensated by the instrument, which only adjusts the electrode slope! This means that, when giving the pH value, it is essential that the temperature at which the pH was measured is also mentioned Example:

pH = 3.52 at 18.2 °C.

The pH value of wines is normally in the range 3.3 to 3.8:

Table wines 3.1 3.6; sparkling wines 3.0 3.6; dessert wines and late-vintage wines 3.4 3.8



P(



P(

#

• Titrant: c(NaOH) = 0.1 mol/L, e.g Merck no 109141, or dissolve 4.0 g NaOH

in CO2-free dist H2O, make up to 1000 mL and mix

• Standard substance: potassium hydrogen phthalate, e.g Merck no 102400

The titrant c(NaOH) = 0.1 mol/L is available commercially as a ready-to-use

solution, its titer has been adjusted by the manufacturer to 1.000 at 20 °C We recommend the use of such a titrant The titer of NaOH solutions is not stable (CO2 absorption from the air) To prevent this absorption as far as possible, soda lime (e.g Merck no 106839) should be filled into the drying/absorber tube

of the Exchange Unit

The titer is determined by comparison with so-called standard substances These hardly change their content at all, are available with a defined degree

of purity, can be dried and are directly traceable to standard reference als (e.g National Institute of Standards and Technology – NIST, USA) Such a standard substance (secondary standard) is potassium hydrogen phthalate,

materi-M = 204.23 g/mol

Potassium hydrogen phthalate is dried overnight in a drying oven at 105 °C and allowed to cool down in a desiccator for at least 1 h Care should be taken that the titrations are carried out at a constant temperature

The titer determination is normally carried out three times and the mean value is used The mean value of the titer is stored in the Titrino, e.g as Common Vari-

able C30.

Approx 200 mg KH phthalate is weighed out into the titration beaker with an accuracy of 0.1 mg and dissolved in approx 50 mL dist H2O The solution is im-

mediately titrated against c(NaOH) = 0.1 mol/L until after the first endpoint.

1 mL c(NaOH) = 0.1 mol/L corresponds to 20.423 mg KH phthalate

• Titrant: c(NaOH) = 0.1 mol/L (method 3)

• Possibly nitrogen from a pressure cylinder

The total titratable acidity is understood to be that fraction of acids contained in the must and/or wine (with the exception of carbonic acid) that are determined when the must is neutralized with NaOH to an agreed or predefined pH value These titratable acids are mainly weak acids (tartaric acid, malic acid, etc.) Their neutral point is above pH = 7.0 (at approx pH = 8.2) It is therefore obvi-ous that lower values will be obtained by titrating to pH = 7.0 than when titrating

to pH = 8.2 To be able to compare the analytical values it is essential that the titration is carried out to the agreed pH value As this latter is defined differently,

it is best to record the whole titration curve and to allow the titrant consumption

up to the given pH value to be recalculated (by the titrator)

CH, EU, Israel and RSA Titration to pH = 7.0

Au and USA Titration to pH = 8.2 or to the point of inflection

The sample is degassed by passing nitrogen through it, by briefly boiling and cooling it down rapidly or under vacuum (CO2 removal) The given sample vol-ume is diluted with CO2-free dist H2O and titrated immediately with c(NaOH) =

0.1 mol/L

A) CH, EU, Israel, RSA

Titrate 10 mL degassed sample plus 10 mL dist H2O (CO2-free) with c(NaOH)

= 0.1 mol/L up to pH = 7.0

B) Au

Titrate 10 mL degassed sample plus 50 mL dist H2O (CO2-free) with c(NaOH)

= 0.1 mol/L up to pH = 8.2 or, preferably, to the inflection point of the titration curve

C) USA

Titrate 5 mL degassed sample plus 100 mL dist H2O (CO2-free) with c(NaOH)

= 0.1 mol/L up to pH = 8.2 or, preferably, to the inflection point of the titration curve

D) SA

Titrate 20 mL degassed sample with c(NaOH) = 0.1 mol/L up to pH = 7.0

Re-sult also given in g/L H2SO4

g/100 mL) and/or in milliequivalents (meq.) per liter.

g/L tartaric acid = EPn x C30 x 7.5 / C00

g/L sulfuric acid = g/L tartaric acid x 0.653

g/100 mL tartaric acid = EPn x C30 x 0.75 / C00

meq./L = EPn x C30 x 0.1 x 1000 / C00

= EPn x C30 x 100 / C00

EPn = mL NaOH up to pH = 7.0 or pH = 8.2 or up to the inflection point of the curve

C00 = sample volume in mL

C30 = titer of the NaOH solution used (method 3)

7.5 = equivalent weight of tartaric acid

The determination of the total titratable acidity is important for:

– musts, to be able to adjust the acidity and add the correct amount of SO2;

– wines, to be able to follow the change in pH and the tartaric acid

concentra-tion

After acid degradation the values for the total titratable acidity normally lie

be-tween 4.0 and 6.5 g/L (red wines 4.0 5.5 g/L, «dry» wines 6.0 9.0 g/L)

Calculation

Remarks

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY



DATE

$%4

Method parameters and calculation method A – red wine

Titration curve method A – red wine

Result method A – red wine



USER DATE P(CINIT lX STOP

$%4 DEF

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY

 DATE

$%4

Method parameters and calculation method A – white wine

Titration curve method A – white wine

Result method A – white wine

 USER

DATE P(CINIT lX STOP

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY



DATE

$%4

Method parameters and calculation method B – red wine

Titration curve method B – red wine

Result method B – red wine

tFR



USER DATE P(CINIT lX STOP

$%4 DEF

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY

 DATE

$%4

Method parameters and calculation method B – white wine

Titration curve method B – white wine

Result method B – white wine

 USER

DATE P(CINIT lX STOP

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY



DATE

$%4

Method parameters and calculation method C – red wine

Titration curve method C – red wine

Result method C – red wine



USER DATE P(CINIT lX STOP

$%4 DEF

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY

 DATE

$%4

Method parameters and calculation method C – white wine

Titration curve method C – white wine

Result method C – white wine

tFR

 USER

DATE P(CINIT lX STOP

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY



DATE

$%4

Method parameters and calculation method D – red wine

Titration curve method D – red wine

Result method D – red wine



USER DATE P(CINIT lX STOP

$%4 DEF

FORMULA

SILO

COMMON

REPORT

MEAN

TEMPORARY

 DATE

$%4

Method parameters and calculation method D – white wine

Titration curve method D – white wine

Result method D – white wine

 USER

DATE P(CINIT lX STOP

• Titrant I: c(NaOH) = 0.01 mol/L, e.g Titrisol, Merck no 109961, or dissolve

0.40 g NaOH in CO2-free dist H2O, make up to 1000 mL and mix

• Standard substance: potassium hydrogen phthalate, e.g Merck no 102400

• Titrant II: c(I2) = 0.01 mol/L (0.02 N) Make up 200 mL c(I2) = 0.05 mol/L, e.g Merck no 109099, to 1000 mL with dist H2O and mix Alternatively: Dissolve 4 5 g potassium iodide, e.g Merck no 105043, in approx 10 mL dist H2O in a 1000 mL round-bottomed flask and add 2.55 g iodine, e.g Merck no 104761 The sealed flask is shaken, without the addi-tion of any more water, until all the iodine has dissolved The solution is then made up to the mark with dist H2O and mixed

• Titrant III: Iodide-iodate solution, c(I2) = 1/128 mol/L (N/64), e.g Titrisol, Merck no 109099, or dissolve 0.5573 g potassium iodate (dried at max

150 °C), e.g Merck no 105051, in approx 700 mL dist H2O Add 3.5 g sium iodide, e.g Merck no 105043, and dissolve; make up to 1000 mL with dist H2O and mix

potas-• Sulfite standard: Weigh out 102.0 mg Na2SO3 w = 98%, e.g Merck no

106657, into a 100 mL volumetric flask, dissolve in O2-free dist H2O, then make up to the mark and mix

1 mL standard contains 1 mg Na2SO3

As the solution is not stable, it must be prepared immediately before use

• Sulfuric acid: w(H2SO4) = 25%, e.g Merck no 100716

• Sodium hydrogen carbonate: NaHCO3, e.g Merck no 106329

• Potassium iodide: KI, e.g Merck no 159226

The titrants c(NaOH) = 0.01 mol/L and c(I2) = 1/128 mol/L are commercially available as ready-to-use solutions; their titers have been adjusted by the manu-facturer to 1.000 at 20 °C We recommend the use of such titrants In contrast,

you must prepare the titrant c(I2) = 0.01 mol/L yourself

Many titrants are unstable, which means that the titer must be checked larly This is done by comparison with so-called standard substances These hardly change their content at all, are available with a defined degree of purity, can be dried and are directly traceable to standard reference materials (e.g National Institute of Standards and Technology – NIST, USA) Such a standard substance (secondary standard) is potassium hydrogen phthalate, M = 204.23 g/mol Unfortunately no such standard substance exists for the direct titer determination of the iodine solutions You must prepare the sulfite standard solution yourself This is done by using a substance whose minimum content is guaranteed by the manufacturer The small error of approx 1% that could occur can, in our opinion, be neglected

regu-Recommended

accessories

Reagents

General

This titrant is unstable as it absorbs CO2 from the atmosphere To prevent f this

absorption as far as possible, soda lime (e.g Merck no 106839) is filled into the

drying/absorber tube of the Exchange Unit

Potassium hydrogen phthalate is dried overnight in a drying oven at 105 °C and

allowed to cool down in a desiccator for at least 1 h Care should be taken that

the titrations are carried out at a constant temperature

The titer determination is normally carried out three times and the mean value is

used The mean value of the titer is stored in the Titrino, e.g as Common

Vari-able C31.

Approx 20 mg KH phthalate is weighed out into the titration beaker with an

accuracy of 0.1 mg and dissolved in approx 30 mL dist H2O The solution is

immediately titrated with c(NaOH) = 0.01 mol/L until after the first endpoint

C 1.2 Orienting Ripper method c(I2) = 0.01 mol/L (0.02 N) Au, SA, USA

This titrant is unstable as iodine is volatile We recommend that you determine

the titer of this titrant at least once per week Care should be taken that the

titra-tions are carried out at a constant temperature

The titer determination is normally carried out three times and the mean value is

used The mean value of the titer is stored in the Titrino, e.g as Common

Vari-able C32.

40 mL dist H2O and 5.00 mL sulfite standard are placed in the titration

bea-ker After the addition of 5 mL w(H2SO4) = 25% and approx 1 g NaHCO3, the

solution is titrated with c(I2) = 0.01 mol/L up to the endpoint (double Pt-sheet

electrode)

1 mL c(I2) = 0.01 mol/L corresponds to 1.2604 mg Na2SO3

Titer = C00 / C01 / EP1

EP1 = mL iodine solution consumed up to the endpoint

C00 = 5 (weight of sulfite standard in mg)

C01 = 1.2604

Calculation of titer

C 1.3 Orienting Ripper method c(I2) = 1/128 mol/L (N/64) CH, RSA

This titrant is relatively stable Nevertheless, we recommend that you determine the titer at least once per month Care should be taken that the titrations are carried out at a constant temperature

The titer determination is normally carried out three times and the mean value is used The mean value of the titer is stored in the Titrino, e.g as Common Vari-

able C32.

40 mL dist H2O and 5.00 mL sulfite standard are placed in the titration beaker

After the addition of approx 1 g KI and 5 mL w(H2SO4) = 25% the solution is

titrated with c(I2) = 1/128 mol/L up to the endpoint (double Pt-sheet electrode)

1 mL c(I2) = 1/128 mol/L corresponds to 0.985 mg Na2SO3

Calculation of titer

Titer = C00 / C01 / EP1

EP1 = mL iodide-iodate solution consumed up to the endpoint

C00 = 5 (weight of sufite standard in mg)

C01 = 0.985

• Titrant II: c(I2) = 0.01 mol/L (0.02 N), method 5, Au, SA, USA

• Titrant III: iodide-iodate solution, c(I2) = 1/128 mol/L (N/64), method 5, CH, RSA

to sulfate (sulfuric acid) by iodine

A double Pt-sheet electrode that is polarized by applying a current (e.g 1 μA) is used for determining the endpoint This is known as bivoltammetry (two elec-trodes polarized by applying a current, the voltage is measured) As long as

an SO2 excess is present, the resulting voltage remains relatively high and proximately constant (about 300 mV) As soon as iodine is present in excess the electrodes become depolarized and the voltage drops toward 0 mV (L-shaped titration curve)

ap-SO2 + H2O = H2SO3 (sulfurous acid)

H2SO3 + I2 + H2O = H2SO4 (sulfuric acid) + 2 HI

As a result of the oxidation of the platinum surfaces (new electrodes or trodes that have not been used for a long time) the electrode response be-comes poorer Either no voltage differences at all or only small ones are ob-tained Mechanical cleaning has no effect The electrode must be regenerated electrochemically:

elec-This is done by connecting the two platinum sheets to the minus pole of a DC source (e.g 4.5 V battery) A further platinum electrode or an iron nail (do not use copper) is attached to the plus pole and both are immersed in a solution

of dilute sulfuric acid, to which a little sulfite can also be added Electrolysis is carried out under stirring for 3 min – gas bubbles should form on the electrode surfaces The electrodes are removed (still under current) and rinsed with dist

H2O This regeneration method is also described on the leaflet accompanying the electrode

Pipet the prescribed amount of sample into a beaker, add sulfuric acid and sibly NaHCO3 and KI and titrate with iodine solution up to the endpoint

pos-A) Au, USA

Pipet 50 mL sample into a beaker, add 5 mL w(H2SO4) = 25% and approx 1 g NaHCO3 and titrate with c(I2) = 0.01 mol/L up to the endpoint

B) SA

Pipet 10 mL sample and approx 20 mL dist H2O into a beaker, add 1 mL

w(H2SO4) = 25% and approx 0.2 g NaHCO3 and titrate with c(I2) = 0.01 mol/L

Pipet 50 mL sample into a beaker, add approx 1 g KI and 5 mL w(H2SO4) = 25%

and titrate with c(I2) = 1/128 mol/L up to the endpoint

The free sulfurous acid is given in mg SO2 per liter sample

1 mL c(I2) = 0.01 mol/L corresponds to 0.641 mg SO2

1 mL c(I2) = 1/128 mol/L corresponds to 0.500 mg SO2

mg/L SO2 = EP1 x C01 x C32 x 1000 / C00

EP1 = mL titrant up to the endpoint

C00 = sample size in mL (50 or 10)

C32 = titer of titrant (method 5)

• For sulfurization of the mash and the must, SO2 is added from a gas cylinder

or, less frequently, a potassium disulfite (K2S2O5) solution is added

«Sulfu-rous acid» is one of the most important must treatment agents It is used

primarily for:

– Inhibiting or killing unwanted microorganisms

Acetic and lactic acid bacteria generally react more sensitively to the

addi-tion of SO2 than yeasts The addition of 100 mg/L SO2 to the must delays

fermentation for only 1 2 days, but has the disadvantage that a large part

of the SO2 is bound to acetaldehyde by the yeasts, which means that the

total sulfurous acid balance is increased to an unacceptable level As a

result only 40 50 mg/L SO2 are usually added

– Inhibiting the oxidation enzymes (polyphenoloxidases)

These enzymes favor the formation of brown-colored entities by oxidation

of the natural colorants and tannins In red wines this color loss could not

be remedied Tyrosinase is deactivated to 90% by the addition of 40 mg/L

SO2 and to 100% by 80 mg/L SO2 The laccase (formed in rotten grapes

by the fungus Botrytis cinerea) is hardly deactivated by the addition of SO2

(brief heating to 70 °C)

• This method also determines ascorbic acid (vitamin C) This latter must be

determined separately and the result corrected accordingly

• The maximum permissible amounts of free SO2 differ greatly according to the

local regulations and are in the range 5 70 mg/L SO2 (Greek white wine up

to 100 mg/L SO2) White wines normally have a higher SO2 content than red

wines

Calculations

Remarks

3/

DATE 5INIT SMPL

%0 3/

3/

DATE 5INIT SMPL

%0 3/

3/

DATE 5INIT SMPL

%0 3/