Citation preview
PowerPoint Presentation GM of Maleta Winery in
Niagara-on-the-
Lake, Ontario (Canada)
Winemaking (Véhicule Press, 2008) &
Electrical Engineer – 20 years in telecom
Copyright © Daniel Pambianchi 2012
Acid–Base Reactions
Acid-RS-Alcohol-Tannin Balance
Acids in juice vs. wine and their characteristics and impacts on
juice/wine
Acidification and Deacidification
Copyright © Daniel Pambianchi 2012
An ionic compound that produces or donates hydrogen ions (H+), aka
protons, or accepts e– pairs, aka an electrophile, in an aqueous
solution.
We normally say that “an acid dissociates into its ions” and
represent the chemical equation as:
HA(aq) H+ (aq) + A−
(aq)
where A− represents the anion of an atom or group of atoms.
Examples
Acetic acid: CH3COOH(aq) H+ (aq) + CH3COO−
(aq)
(aq)
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Copyright © Daniel Pambianchi 2012
An ionic compound that produces or accepts hydroxide ions (OH−), or
donates e– pairs, aka an nucleophile, in an aqueous solution.
BOH(aq) B+ (aq) + OH−
(aq)
where B+ represents the cation of an atom or group of atoms.
Examples
(aq)
(aq)
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Copyright © Daniel Pambianchi 2012
As we are dealing with aqueous solutions, the subscript (aq) is
usually not written and often H2O is written over the arrow
symbol.
HA(aq) H+ (aq) + A−
which can also be written as:
HA + H2O H3O + + A−
Water can behave as an acid or as a base; the reaction is
represented as:
H2O(l) + H2O(l) H3O +
(aq) + OH− (aq)
Copyright © Daniel Pambianchi 2012
An acid with only one hydrogen atom capable of dissociating is
called a monoprotic acid.
Some acids have extra hydrogen atoms capable of dissociating.
General equation for a diprotic acid:
H2A(aq) H+ (aq) + HA−
H2A(aq) H+ (aq) + HA−
(aq)
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Acetic acid, C2H4O2, CH3COOH, CH3(COOH)
Diprotic acids
H2T(aq) H+ (aq) + HT−
(aq) H+ (aq) + T2−
Triprotic acid
Copyright © Daniel Pambianchi 2012
Notice that many wine acids have a COOH group – this is called a
carboxylic group – hence these wine acids are carboxylic acids.
Sometimes called hydroxy acids.
Lactic acid is a monocarboxylic acid; tartaric acid is a
dicarboxylic acid; citric acid is a tricarboxylic acid.
Carboxylic acids are central in biochemical systems (i.e. yeast and
bacteria fermentations) as well as in wine chemistry
(enology).
Most often involved in decarboxylation reactions where CO2 gas is a
by-product.
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Copyright © Daniel Pambianchi 2012
Strong acids & bases almost completely dissociate (ionize) into
their ions, i.e. the reaction is favored to the right and is
represented by the symbol .
Weak acids & bases dissociate into their ions to a much smaller
extent until the reaction is in equilibrium, and is represented by
the symbol .
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Copyright © Daniel Pambianchi 2012
The extent of ionization of an acid is determined by its
dissociation constant Kd, which is simply the ratio of ion
concentrations (shown in [ ]) to free acid concentration at
equilibrium, or:
Kd = [H3O +] [A−] / [HA]
the greater the Kd, the stronger the acid.
But Kd have very low values (e.g. 9.10 x 10−4) & their
scientific format is cumbersome to work with – enter pKa.
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Copyright © Daniel Pambianchi 2012
pKa is calculated as the negative logarithmic (base 10) value of Kd
or:
pKa = –log10Kd
So now, for example, if Kd = 9.10 x 10−4, then pKa = 3.04.
the smaller the pKa, the stronger the acid.
pKa increases in alcoholic solutions, but we’ll simplify our
analysis using pKa values in aqueous solutions.
pKa represents the value at which substances at equilibrium exist
in equal proportions.
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RCOOH Weak carboxylic acids 3–5
Pure H2O Acid/Base 14
ROH Alcohols 15–19
NH3 (Ammonia) Base ~ 35
R stands for substituents, e.g. in acetic acid (CH3COOH),
R=CH3
and in ethanol (CH3CH2OH), R=CH3CH2.
pKa values must be specified at what temperature they were
measured; usually at 25°C (77°F).
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Copyright © Daniel Pambianchi 2012
The first dissociation equilibrium has a first pKa of pKa1, the
second pKa2, etc.
pKa1 > pKa2 > pKa3 …
(aq)
For example, tartaric acid has pKa1 = 2.98 and pKa2 = 4.34.
pKa1 pKa2
Copyright © Daniel Pambianchi 2012
Acidity is a measure of the concentration of acids in solution and
is expressed in g/L or %; for example, 0.5% tartaric acid is
equivalent to 5 g/L. Small concentrations are expressed in
mg/L.
pH is a measure of the concentration of H3O + ions
and therefore a measure of the strength of acidic (or basic)
solutions. It is unitless and is calculated as:
pH = –log10[H3O +]
solution.
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Copyright © Daniel Pambianchi 2012
pH range is 0–14. pH of pure water is 7 (neutral).
pH < 7.00 is an acidic solution; the lower the pH, the more
acidic the solution. Juice and wine are acidic solutions.
pH > 7.00 is a basic solution; the greater the pH, the more
alkaline the solution.
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Copyright © Daniel Pambianchi 2012
pKa can be shown to be the pH at which two substances in
equilibrium are present in equal proportions.
Example: Tartaric acid (pKa1=2.98, pKa2=4.34)
0 5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100
[H2T] [HT–] [T2–]
Copyright © Daniel Pambianchi 2012
pKa2 of wine acids is always greater than wine pH, which is usually
in the 3.00–4.00 range (more on this later).
So we can greatly simplify our acid analysis by ignoring the second
(and third) dissociation and assume that it contributes
insignificantly to acidity.
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Copyright © Daniel Pambianchi 2012
In general, an increase in acidity causes a decrease in pH, and
vice versa, but …
Consider the general dissociation equation of an acid:
HA + H2O H3O + + A−
to [HA], i.e. the concentration of the undissociated acid.
This means that there can be instances where acid concentration
increases without an increase in pH, or vice versa.
This is known as the buffering effect.
Buffer capacity is exceeded when there is a change in pH.
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Acid–base reactions are involved in juice/wine deacidification
processes and titration procedures for measuring total
acidity.
The reactions we are mainly concerned with are neutralization
reactions with the generalized equation:
HA + BOH AB + H2O
AB is a salt that can precipitate depending on its solubility;
usually depicted as AB(s) or AB↓.
Solubility of salts involves some more intricate knowledge of
compound chemistry but, in general, salts are more soluble at
higher temperature, i.e. they can precipitate at low
temperature.
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First reaction
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Summarized reaction
Why is this all important?
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H2T=150 g CaCO3=100 g K2CO3=138 g
In example #1, using CaCO3, we need 100 g of CaCO3 for every 150 g
of H2T to deacidify.
In example #2, using K2CO3, we need 138 g of K2CO3 for every 300 g
(2x150 g), or 69 g for every 100 g of H2T to deacidify.
So less K2CO3 is required (CaCO3 also leaves an earthy
taste).
Predicting acidity reduction: 1 g/L of K2CO3 reduces acidity by
approx. 100/69 g/L or 1.5 g/L.
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Copyright © Daniel Pambianchi 2012
Calculating acidity and pH involves some complex math and
assumptions beyond the scope of this session. We’ll simply be
concerned with how to measure these.
pH is easy; just need a pH meter. Make sure to calibrate pH meter
before every use and store according to manufacturer’s
instructions.
+].
Copyright © Daniel Pambianchi 2012
By neutralizing all the acid present in a solution with a base, a
process known as acid-base titration, the amount of base used
corresponds to the total titratable acidity of the sample.
The point at which all the acid is neutralized is called the
equivalence point or titration endpoint.
It can be visually detected by adding a color indicator solution (a
weak acid, e.g. phenolphthalein ) whose color varies with pH; it
changes from a colorless color as a weak acid to a pinkish color at
the titration endpoint to a dark pink.
Color change may be difficult to assess, esp. with reds. Titrate
using a pH meter to a pH of 8.2.
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Total Acidity = Total Titratable Acidity
But in juice/wine, alkaline metal ions (Na+, Ca2+, etc.) neutralize
weak acids and therefore reduce total titratable acidity, and
so:
Total Acidity = Total Titratable Acidity + [alkaline metal
ions]
In winemaking, TA always refers to total titratable acidity .
Total titratable acidity then refers to the concentration of what
we call fixed acids, i.e. non- volatile.
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Copyright © Daniel Pambianchi 2012
Total Titratable Acidity is calculated based on the amount of NaOH
used, as follows:
TA (g/L) = ( 75 × mL of NaOH × N NaOH ) / mL of sample
where N NaOH is the concentration of the NaOH solution.
Example
If 4.5 mL of 0.10 NaOH solution was used to titrate a 5-mL wine
sample, then:
TA (g/L) = (75 × 4.5 × 0.10 ) / 5.0 = 6.8 g/L or 0.68%
In multi-acid solutions where acids all have different MW, one acid
is used as a reference (i.e. all calculations are based on its MW)
– in wine, tartaric acid is the reference in NA.
“7.0 g/L TA” means “7.0 g/L of TA as if all acids were tartaric
acid”
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Copyright © Daniel Pambianchi 2012
But don’t fuss too much with how precise your measurement is and
how close you are to the equivalence point because:
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BUT …
Make sure your NaOH solution is fresh; rotate every 6 months and
keep container well stoppered in cool place.
Make sure you know the concentration of the NaOH solution, i.e.
0.1N vs. 0.2N etc.
Standardize NaOH solution with potassium acid phthalate (KaPh)
before every test session.
Titrate KaPh sample as you would for wine, then:
N NaOH = (mL of KaPh × N KaPh ) / mL of NaOH
And then …
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Copyright © Daniel Pambianchi 2012
But juice/wine is again complicated by the presence of volatile
acids (e.g. acetic acid), meaning these must be measured by steam
distillation. The sum of volatile acids is known as volatile
acidity or VA.
Here too, since acetic acid is the major VA in wine, it is used as
the reference in VA measurements, i.e. “0.3 g/L VA” means “0.3 g/L
of VA as if all VAs were acetic acid.”
VA magnifies the taste of fixed acids and tannins but, itself, is
masked by high levels of sugar and alcohol.
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Copyright © Daniel Pambianchi 2012
Use the Pearson Square to determine the TA of a blend of two or
more solutions.
Pearson Square cannot be used for pH since this is a non-linear
relationship and involves buffering effects.
A D
A = concentration of solution A or wine to be used
B = concentration of solution B or the wine to be “corrected”
C = calculated or desired concentration
D = number of parts of solution A or wine to be used and is equal
to C–B
E = number of parts of solution B or wine to be “corrected” and is
equal to A–C
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“A wine tolerates acidity better when its alcoholic degree is
higher; acid, bitter and astringent tastes reinforce each
other;
the hardest wines are those which are at the same time acid
and also rich in tannins; a considerable amount of tannin is
more acceptable if acidity is low and alcohol is high.
The less tannic a red wine is, the more acidity it can
support
(necessary for its freshness); the richer a red wine is in
tannins
(necessary for its development and for its longevity) the
lower
should be its acidity; a high tannin content allied to a
pronounced acidity produces the hardest and most astringent
wines.”
Peynaud, Émile. The Taste of Wine: The Art and Science of Wine
Appreciation. Translated by
Michael Schuster. London, England: Macdonald & Co. (Publishers)
Ltd, 1987.
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Acidity
Alcohol
Flat, thin, insipid Alcoholic, supple to
mellow, rich to heavy
Acidity
Sweetness
Tannin
imbalance
imbalance
Tartaric 1–7 1–7 Decreases during cold stabilization
Malic 1–4 0–4 Decreases slightly during alcoholic fermentation
by
certain yeasts; can be completely converted by MLF
Lactic 0 1–4 Mainly from MLF but a small amount also produced
during yeast fermentation
Citric 0.15–0.30 0.15–0.30 A small amount is converted to acetic
acid during MLF
Succinic 0 0.5–1.5 By-product of yeast fermentation
Acetic 0* 0.2–0.4 By-product of yeast and LAB fermentations.
*Present in significant concentrations in spoiled grapes.
Total 6–12 6–12
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Copyright © Daniel Pambianchi 2012
Tartaric acid remains fairly constant once synthesized in grapes,
and relatively unaffected by alcoholic fermentation.
Malic acid starts decreasing at veraison.
Cool-climate or poor-vintage varietals will have higher acidity due
to malic acid and lower pH.
What is the ideal TA range?
Really depends on style.
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Ideal pH range: 3.2–3.6
Below 3.2, wine is very acidic and harsher.
Above 3.6, wine is at high risk of microbial spoilage and requires
more sulfite as SO2 is less effective at higher pH.
And remember – stems decrease TA with a slight increase in
pH.
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Copyright © Daniel Pambianchi 2012
Many other acids … but most are very weak &/or only present in
minuscule amounts
Phenolic acids
o Non-flavonoids (hydroxybenzoic and hydroxycinnamic acids)
o Example of an HCA: Caftaric acid – major phenolic acid
responsible for phenolic oxidation in musts
Oxalic acid
Fumaric acid
Amino acids
H2SO3 and H2CO3 contribute to VA.
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Tartaric 150 2.98 4.34
Citric 192 3.13 4.74
Malic 134 3.46 5.10
o Carbonate salts
o Double-salt precipitation
o Calcium sulfate
o Phosphoric acid
o Schizo. pombe
o S. uvarum
GENERAL CONSIDERATIONS
Be sure you understand wine’s buffering capacity and the impacts on
TA and pH.
TA impacts pH, and pH affects pigment polymerization & color
stability in reds, microbial stability, effectiveness of free SO2
& bentonite treatments, solubility of proteins, oxidative and
browning reactions, and freshness.
Often the challenge is having to effect one without affecting the
other, e.g. increase TA without affecting pH in low-TA, low-pH
wine.
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Copyright © Daniel Pambianchi 2012
GENERAL CONSIDERATIONS (cont’d)
Best to make major acid adjustment before alcoholic fermentation to
allow yeast & bacteria to perform under balanced
conditions.
The challenge for home winemakers is determining relative
concentrations of tartaric and malic acids.
Enzymatic test
Paper chromatography
Freezer test
FREEZER TEST
(adapted from Clark Smith in January 2012 issue of Wine &
Vines)
Prepare a 10% tartaric acid solution.
Measure the TA of a juice sample.
Using a 100-mL juice sample, monitor the pH and incrementally
add
the 10% tartaric acid solution until the juice reaches a pH of
3.6.
Transfer the sample to a 250-mL flask, stopper, and place in
the
freezer overnight.
Transfer the sample from the freezer to the refrigerator to let
the
sample thaw. Once thawed, you should notice tartrate crystals
at
the bottom of the flask.
Transfer, or preferably, filter the sample to a beaker to separate
out
the crystals.
Measure the TA. A large TA drop means that the juice has high
potassium content; otherwise, high TA is likely due to high
malic
acid content.
Tartaric acid – best but expensive.
Malic acid – look for D-malic as it does not get converted to
lactic acid by LAB. Commercial malic acid is usually
D,L-malic.
Lactic acid – softer but 70% more required than tartaric acid to
achieve same effect.
Citric acid – common acidulant in food/beverage industries;
effective but can be metabolized into diacetyl and acetic acid by
LAB in MLF.
Acid blends – only recommended if you know exact contents &
concentrations; many include citric acid.
Fumaric acid – common acidulant in food/beverage industries;
recommended for increasing TA where MLF is not desired; inhibits
MLF at > 500 mg/L.
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3:2:1 (T/M/C)
Fumaric acid 116 +1.3 +1.0 –0.1
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H2T + KHCO3 KHT + H2O + CO2
Deacidifying agent MW (g) Amount
(g/L)
53
SIHADEX, Acidex, Neoanticid
Comprise calcium carbonate (CaCO3) as the deacidifying agent with a
small volume (e.g. 1%) of calcium malate-tartrate as a seed.
Quick and efficient
Recommended for high-TA musts/wines with a greater ratio of malic
acid.
We’ll look at this closer once we examine dissociation behaviors of
H2T and H2M.
54
pH Tartari
Succini
c
Fumari
c
Most important (and strongest) acid in wine.
Contributes to wine’s backbone and structure, gives freshness, and
provides protection against spoilage effects.
The acid of choice for increasing TA or decreasing pH.
Can be reduced using carbonate salts, double-salt precipitation
(and amelioration, blending and electrodialysis).
But highly affected by cold temperatures in the presence of
potassium ions; used as a TA- reducing technique.
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0 5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100
%
[H2T] [HT–] [T2–]
Copyright © Daniel Pambianchi 2012
At pH < 3.70, a [HT−] reduction (e.g. from cold stabilization)
causes a shift in equilibrium to the right, which causes an
increase in [H+], resulting in a decrease in pH.
At pH > 3.70, a [HT−] reduction causes a shift in equilibrium to
the left, which causes a decrease in [H+], resulting in a increase
in pH.
58
OBJECTIVES
To protect wine against the effects of cold storage or
handling.
To reduce TA by reducing tartaric acid content.
EFFECTS
Harmless but affect appearance.
Affects primarily white wines due to higher tartaric acid
content.
Must be avoided in sparkling wine; tartrates will become nuclei for
CO2 formation and cause excessive gushing during disgorging in
traditional- method production.
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From soil and/or additives, e.g. potassium bicarbonate, calcium
carbonate.
K+: 1–2 g/L, Ca2+: 30–200 mg/L
Combine with HT– and T2– to form soluble potassium bitartrate and
calcium tartrate salts.
Solubility of tartrate salts decreases as ethanol increases or
temperature decreases, and causes crystallization (tartrate
instability).
The greater the concentration of H2T, K+ and Ca2+, the greater the
potential for tartrate instability.
HT– + K+ KHT T2– + Ca2+ CaT
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Copyright © Daniel Pambianchi 2012
Other factors affecting crystallization:
Polyphenols, sulfates and proteins.
Can bind with tartaric acid or its ions and thus reduce
availability of these ions to form KHT or CaT.
Crystallization causes a decrease in total acidity (TA) due to
decreasing tartaric acid concentration. Difficult to quantify; can
expect a drop of up to 1.6 g/L.
Impact of pH depends on wine pH. Difficult to quantify; can expect
a change between 0.1–0.2.
62
Effects of pH
As pH increases, [H2T] decreases and both [HT–] and [T2–]
increase.
By increasing [HT–] and [T2–] we can decrease [H2T] by adding a
seed, e.g. potassium bitartrate (KHT) or calcium tartrate
(CaT).
But! At pH =3.7, [HT–] is at its maximum and decreases as pH
increases further, and causes re-equilibrium. What this
means:
pH < 3.7, tartrate crystallization causes a decrease in TA and
pH.
pH > 3.7, tartrate crystallization causes a decrease in TA but
an increase in pH.
63
Fridge Test
Hold sample at 0ºC (32ºF) for 4–6 days; no crystals = wine is
stable.
Conductivity Test
Uses a conductivity meter.
Stability determined by measuring conductivity drop (% ΔC);
considered stable if % ΔC < 5%.
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Hold wine below 0ºC (32ºF) for several days or more.
Add KHT as a seed to hasten crystallization
50–100 g/hL or 10–20 g in a 20-L/5-gal carboy
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But slowly hydrolyzes into tartaric acid; inhibition potential
diminishes and the potential of tartrate formation increases.
Requires wine to be stored at cold temperature.
Recommended primarily for early-drinking wines. Not very
stable.
Add 10 g/hL; 2 g in carboy.
Add gum arabic to enhance action.
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CMC is a cellulose gum polymer.
Common food additive used as a thickener and to stabilize
emulsions.
Inhibits KHT formation in wine.
Good solubility at both cold and hot temperatures.
CMC has good stability over time and at a wider range of
temperatures.
First test for protein stability to avoid CMC-protein colloidal
instabilities.
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Copyright © Daniel Pambianchi 2012
Can also interact with anthocyanins (color pigments) in red and
rosé wines, resulting in color loss and colloidal
instabilities.
Color can be stabilized using gum arabic prior to CMC
treatment.
Add up to 100 mg/L.
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Copyright © Daniel Pambianchi 2012
Very significant acid in wines from cool-climate regions or from
poor vintages; can exceed tartaric acid content.
Has a very sharp taste; same acid as found in green apples.
Can be reduced (and converted to lactic acid) by MLF, double-salt
precipitation, malolactic wine yeast (ML01), Schizo. pombe yeast
(and amelioration, blending).
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0 5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100
%
[H2M] [HM–] [M2–]
knowing that hydrogen malate can be precipitated
at high pH, higher than 4.30 (compared to
hydrogen bitartrate which peaks at 3.65, i.e. in
wine pH range), and that hydrogen malate and
malate ions exist in equal proportions at a pH of
around 5.1 (see figure). Note that precipitation
must be made to happen at a pH higher than 4.30;
otherwise, more tartrate salt precipitates.
H2T H+ + HT− 2 H+ + T2−
H2M H+ + HM− 2 H+ + M2−
2.98 4.34
5.10 3.46
0
10
20
30
40
50
60
70
80
90
100
%
[H2M] [HM–] [M2–]
volume of juice by adding a calculated amount of calcium
carbonate (CaCO3) as to raise the pH to 4.30 and cause the
double-salt to form and precipitate and the TA to drop close
to
zero, and then add the treated volume back to the batch to
complete the deacidification procedure. As calcium carbonate
is added and pH increases, calcium tartrate begins to
precipitate until a pH of 4.3 and then the calcium malate
tartrate
(Ca2MT) salt starts to form and precipitate; therefore, the
amounts of tartaric and malic acid precipitated are not
exactly
equal. The reaction is quick and the salts are relatively
insoluble and heavy and therefore precipitate quickly, which
must be removed promptly from the juice; it should also be
filtered.
H2T + H2M + 2 CaCO3 CaT + CaM + 2 H2O + 2 CO2 Ca2MT + 2 H2O + 2
CO2
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Copyright © Daniel Pambianchi 2012
Only found in wines that have gone through MLF, i.e. the result of
malic acid conversion.
Can also be found in wines with various types of spoilages.
Has a much softer taste than malic acid; same acid as found in
dairy products.
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0 5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100
%
[HL] [L–]
Copyright © Daniel Pambianchi 2012
Naturally occurring in grapes; adds some freshness and zing but can
impart sharpness if excessive (not usually a problem unless added
exogenously).
Metabolized into acetic acid and diacetyl by LAB during MLF !!
Therefore, only add citric acid after MLF is complete and wine has
been stabilized if you want to add citric acid. Tartaric acid
remains the acid of choice to increase TA.
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0 5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100
%
pH
Relative concentrations of Molecular Citric Acid and Citrate Ions
vs pH
[Citric acid] [Hydrogen citrate] [Dihydrogen citrate]
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Acid found in vinegar and almost solely responsible for VA.
Theoretically, there should not be any in perfectly- harvested
grapes; that seldom happens, so there is always some small
amounts.
Yeast fermentation produces small amounts (below detection
threshold), but adds flavor complexity to wine.
Detection threshold is ~ 0.6 g/L; above 2.0 g/L, the wine is
considered spoiled.
Dehydrated, damaged and/or rotten grapes can have high amounts, but
then, you may have other, more serious problems (i.e. polyphenol
oxidation by laccase enzymes).
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0 5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100
%
[Acetic Acid] [Acetate]
Copyright © Daniel Pambianchi 2012
By-product of yeast fermentation.
Proportional to the amount of ethanol produced, typically in the 1
g/L range but can be as much as 2 g/L depending on yeast strains.
Bayanus strains, for example, produce higher amounts.
Can also impart slightly salty and bitter tastes.
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Due to residual, dissolved CO2.
Many metabolic processes produce CO2.
Unstable and so has a tendency to decarboxylate spontaneously into
CO2 and H2O under acidic conditions found in wine.
CO2•H2O H2CO3 H+ + HCO3 − 2 H+ + CO3
2−
0 5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
100
%
Relative concentrations of Carbonic Acid and Carbonate Ions vs
pH
[H2CO3] [HCO3–] [CO32–]
Copyright © Daniel Pambianchi 2012
A small amount of carbonic acid is desirable to maintain freshness
and balance, as well as to help volatize all those wonderful
aromas.
Every style of wine has an ideal residual CO2 content range, which
depends on wine chemistry—namely, acidity, and polyphenolic and
alcoholic concentrations—and the winemaker’s preference.
Wine type/style Recommended
CO2 range (mg/L)
White 500–1800
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Used to lower pH without significantly affecting TA.
Reacts with tartaric acid to form calcium tartrate precipitate, and
lower pH, with any molecular tartaric acid available to ionize
further, and maintain TA.
H2T + CaSO4 CaT + SO4 2− + 2 H+
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Copyright © Daniel Pambianchi 2012
Aka orthophosphoric acid; a common acidulant in food/beverage
industries, particularly in cola drinks as well as active buffering
agents or pH- adjusting ingredients.
H3PO4 H+ + H2PO4 −
Practice of adding water to reduce acidity.
Dilutes color, aromas, flavors and many other compounds that
contribute to the quality of the wine.
H2O also binds to anthocyanins to reduce color – known as bleaching
effect.
Adding 20% H2O reduces TA by ~10% because water increases the
solubility of KHT and less precipitates before and after
fermentation. (Zoecklein’s Enology Notes #5).
Because of wine’s buffering capacity, amelioration does not
significantly alter pH.
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Copyright © Daniel Pambianchi 2012
Used to convert the sharper L-malic acid to the softer L-lactic
acid (and CO2).
Also to decrease TA, but raises pH; so beware!
And for stylistic reasons for those varietals that are
MLF-compatible.
Difficult to predict TA/pH changes since those are pH-dependent,
with 3.4 being the focal point (Kunkee, 1977).
TA was shown to drop by 1 g/L in wine pH range, except at a pH
around 3.4 where it dropped by 2.0 g/L; and pH increased by 0.1 at
the low wine range pH and by 0.2 at the high end.
Remember … do not add citric acid if you will conduct MLF.
88
Schizo. pombe
It has been demonstrated experimentally that 0.1% alc/vol ethanol
is produced from approximately 2.3 g/L of malic acid (Scott Labs
ProMalic), and so, ethanol increase in high-malic wines is
relatively small compared to total ethanol content in wine.
S. uvarum
Max. theoretical yield of 2 moles of L-malate per more of glucose,
i.e. 180 g of glucose yields 268 g of malic acid.
89
http://TechniquesInHomeWinemaking.com
http://TechniquesInHomeWinemaking.com/blog
Pambianchi, Daniel. TECHNIQUES IN HOME WINEMAKING: The
Comprehensive Guide to Making Château-Style Wines. Newly- Revised
& Expanded Edition. Montréal: Véhicule Press. 2008.
Copyright © Daniel Pambianchi 2012