Acids

Overview

Many different acids are present in wines. For the needs of this paper, we will stay focus on these 4 :

Tartaric (TH₂) : an inherent winee acid, which is synthecized and stocked in such organs of the young plants as leaves ands berries. It has a huge impact on the TA of wines/juices and is often used to adjust the acidity and pH.

Malic (MH₂): It is synthecized in the organs of an adult plants (leaves and berries) through the synthesis of the sugars. During the ripening process, it is used by the winees as a metabolism resource for energy production. This means that its final concentration after the ripening process will have strongly decreased. It is also used during the winemaking process for the acidification of wines and juices.

Citric (CiH₃) : It is mostly found in rotten berries infected by Botritis cinerea or in other processes as "passerillage". It is not recommended to use it to adjust acidity but it is usefull to add it at the bottling stage to prevent iron hazes.

Lactique (LH) : Its synthesis is due to the bacteria metabolism that occurs during the malolactic fermentation (FML)This fermentation occurs after alcoholc fermentation and involved lactic bacteria (Oenoccocus oeni) which transform malic acid into lactic acid. Winemakers can choose to let theirs wines go through this fermentation depending on the desired wine style. The FML is a excellent way to soften wines, decreasing acidity, stabilizing and create new aromas.. It can also be added in wines/juices for its acidifying properties.

Total acidity (TA)

The TA represents the sum of all titratable acids in a wine/juice sample (mainly : tartaric, malic and citric).

It is expressed in milliequivalents per milliliter (meq/L) or can be converted on current acids scales, in g/L of tartaric acid (TH₂) or in g/L of sulfuric acid (H₂SO₄). During the winemaking process, the TA will be extremely variable due to the characteristics changes of the medium (temperature, alcohol, sugars...). Winemakers can influence the AT by using chemicals, physics techniques or natural process (FML). Some are described below.

Other ways to decrease acidity

Run a FML.

Electrodialysis.

The use of malic's metabolizer yeast (Schyzosaccharomyces).

Diminishing the winee's vigor by decreasing the surface of the leaves, increasing weeds competition, diminishing nitrogen nutrients, remowineg leaves.

Blending.

Tips

An earlier acidification before or during fermentation will not affect it or delay FML's launch but an acidification right before FML will.

A good pH will prevent micro-organism spoilages.

It is strongly discouraged to use citric acid for acifying juices/wines. In fact, it can be metabolized by lactic bacteria and produce diacetyl and acetic acid.

It is usually recommanded to aim around 3.3 pH and stay below 8 g/L TH₂ (5.2 g/L H₂SO₄) for whites/rosés. As for red wines, aim at 3.4 pH and stay below 7.5 g/L TH₂ (4.9 g/L H₂SO₄).

A low pH will facilitate settling down heavy lies and tartar precipitation.

Adding tartaric acid may cause potassium bitartrate precipitation.

To insure good homogeneization, acids must be first dissolved in a small wine/juice volume then added to the tank during pumping over (red) or mixing (whites).

The gap between chemistry and practice

Chemistry

meq/L	gH₂SO₄/L	gTH2/L	gMH2/L	gLAC/L

Acid	Conversion (g/L)	Tartaric acid (g/L)	Sulfuric acid (g/L)	Lactic acid (g/L)	Malic acid (g/L)	Citric acid (g/L)
Tartaric
Sulfuric

In practice

You must be extremely careful when acidifying or deacidifying time comes up because the effects could be very different compare to the theory..

In fact, it is really complicated to anticipate the final TA concentration for different reasons :

The manipulation of the berries (pressing, destemming, pumping, maceration...) will affect the release of malic acid, tartaric acid, potassium and others acids (succinic acid).

Temperature variations and ethanol synthesis modify molecule solubilization.

Juice/wine chemical and physical equilibrium will affect tartar precipitation.

It is recommanded to adjust pH and TA right before or at the beginning of the alcoholic fermentation depending on the final wine desired. In case you still need one more adjustement, pH can be changed after the FML.

Acidification

Lab trial
Prepare a 100 g/L tartaric acid solution (10g in 100 mL of distilled water) and make a lab trial. Try different concentrations, measure and taste each solution before selecting the one that fits your expectations. You can use our lab trial tutorial to help you.

Increase the TA Warning, the last section of the table named "pH should decrease by" is purely theoric. It is highly recommended to proceed a laboratory trial to confirm the new pH and TA values ! You can follow the protocol above and use our lab trial tutorial to help you.

Current TA (g/L of )	Desired TA	Volume (hL)	Lactic acid stock concentration

Tartaric acid (kg)	Malic acid (kg)	Lactic acid (L)	pH should decrease by... (depends on tartaric)

Decrease the pH in theory Warning, This table is strictly theoric and it is here to give you some guidance. It is highly recommended to proceed a laboratory trial to confirm the new pH and TA values ! You can follow te protocol above and use our lab trial tutorial to help you.

Current pH	Desired pH	Volume (hL)

Tartaric acid (kg)	TA should increase by... (g/L of )

Deacidification

Lab trial
Prepare a 50 g/L solution of KHCO₃ or CaCO₃ (5 g in 100 mL of distilled water) and make a lab trial. Try different concentrations -let it sit for at least 2hours in the fridge and shake each becher every 15min-, then filter, measure and taste each solution before selecting the one that fits your expectations. You can use our lab trial tutorial to help you.

Deacidification

Calcium carbonate (CaCO3) is used during winemaking process and make calcium tartar crystals (CaT) precipitate.

Potassium bicarbonate (KHCO₃) is used for small corrections to make potassium bitartrate cristals (KTH) precipitate

Dissolve the product in a small volume of juice/wine then add it while pumping over (reds) or mixing tank (whites).

Adding the product will create a dense foam (CO₂), in consequence, be sure there's enough space to avoid overflows.

1-2 weeks after addition, mix the bottom of the tank to increase crystals precipitation.

1 g/L potassium bicarbonate decrases TA by 0.5 g/L H₂SO₄ plus 0.25 g/L after mixing which means 0.75 g/L H₂SO₄ or 1.15 g/L TH₂ in total.

1 g/L calcium carbonate will decrease TA by 1 g/L de H₂SO₄ or 1.53 g/L TH₂.

Current TA	Desired TA	Volume (hL)	Product

Required quantity (kg)

French legislation

Careful, depending on appellation, some process may change or can be restrained. See the appellation's legislation for more information.

Process	Medium	Maximum legal dose
Acidification (commom)	Must	+0.98 g/L de H₂SO₄ soit +1.5 g/L de H2T
Acidification (commom)	Wine	+1.63 g/L de H₂SO₄ soit +2.5 g/L de H2T
Acidification (tartaric)	Must	150 g/hL
Acidification (tartaric)	Wine	250 g/hL
Acidification (malic)	Must	130 g/hL
Acidification (malic)	Wine	230 g/hL
Acidification (lactic)	Must	180 g/hL
Acidification (lactic)	Wine	300 g/hL
Deacidification (commom)	Both	-0.65 g/L de H₂SO₄ soit -1 g/L de H2T
Deacidification (Potassium bicarbonate)	Wine	150 g/hL
Deacidification (Calcium carbonate)	Wine	65 g/hL
Iron haze	Wine	1 g/L ofcitric acid for bottling