Daniel Pambianchi ACIDS IN WINE - nys-homewine.info

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
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)
6
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)
7
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)
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)
9
Acetic acid, C2H4O2, CH3COOH, CH3(COOH)
Diprotic acids
H2T(aq) H+ (aq) + HT−
(aq) H+ (aq) + T2−
Triprotic acid
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.
11
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 .
13
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.
14
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).
16
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
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.
18
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.
19
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–]
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.
21
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.
22
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
24
Summarized reaction
Why is this all important?
25
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.
26
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.
+].
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.
29
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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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 …
32
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.
33
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
34
“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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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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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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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–]
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.
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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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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.
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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.
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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.
67
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.
68
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.
69
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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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–]
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]
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–]
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+
85
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.
87
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.
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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.
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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.

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Daniel Pambianchi ACIDS IN WINE - nys-homewine.info