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FermCalc - Acidity Calculations Introduction The Acidity Calculations panel performs two types of calculations: titration and acid balancing. The titration calculator determines the acidity from the results of a titration with NaOH. The acid balancing calculator determines the amount of acid to add to a given must or wine to raise the acidity to a specified level, and it can also estimate the amount of calcium carbonate, potassium carbonate, or potassium bicarbonate required to reduce the acidity to a target level. Making a Calculation To make a calculation, follow these steps:
Titration Calculation Details Acid titration makes use of the neutralization reaction between NaOH and the acids present in wine. In this reaction, the OH- ions donated by the NaOH and the H+ ions donated by the wine acids combine to form water, H2O. The reaction is complete when all of the H+ ions have been neutralized by OH- ions. Since each OH- ion neutralizes one H+ ion, we can write a balance between the H+ and OH- ions as:
where ia = number of H+ ions donated by each molecule of acid The mass of the acid in solution is simply the acidity multiplied by the volume or:
where a = acidity, grams/liter Combining equations (1) and (2) and solving for acidity we get:
By titrating for acidity, all we've really determined is the number of available H+ ions in the solution and not the types of acid present. For this reason we must choose an acid as a reference in order to express the acidity as a concentration. Tartaric acid is frequently used as a reference, and is the default acid reference in FermCalc. For tartaric acid, mwa is 150.09, and ia is equal to 2, so equation (3) becomes: Back to top Acid Balancing Calculation Details There are two scenarios we need to consider for this calculation.
For the first scenario, FermCalc will calculate the amount of acid required to increase the acidity to the specified target. For the second case FermCalc will calculate the amount of deacidifier to add. If you are diluting a must with water, blending juices, or blending wines to adjust acidity, use the Blending panel to calculate the proportions required to achieve the desired acidity. Case 1: Initial Acidity is Less Than the Target Acidity For this case we'll be adding acid to increase the acidity. FermCalc first converts the initial and target acidity values to the tartaric reference using the conversion factors explained in the Acidity Conversions discussion. To calculate the required addition of the selected acid we need to write a molar balance equation for the H+ ions in the wine. The final (or target) number of H+ ions must equal the initial number of H+ ions plus the number of H+ ions added, or:
where it = number of H+ ions per molecule for tartaric acid Rearranging to solve for the mass of acid to add we get:
Values of molecular weight and number of H+ ions per molecule are shown in the table below.
For Acid Blend, the composition is assumed to be 40% tartaric, 40% malic, and 20% citric acids. Back to topCase 2: Initial Acidity is Greater Than the Target Acidity For this case we'll need to add either calcium carbonate (CaCO3), potassium carbonate (K2CO3), potassium bicarbonate (KHCO3), or potassium hydroxide (KOH) to reduce the acidity. All of these work by neutralizing tartaric acid, or H2T, where T represents a tartrate ion (C4H4O6). The reaction equations are (based on Margalit, 2004, and Beelman et. al., 1979):
To calculate the required amount of any of these additives, we need to know their molecular weights as well as the number of H2T molecules that are neutralized by each molecule of deacidifier. These parameters are tabulated below.
We can calculate the required mass of deacidifier to add by balancing the initial and final quantities of H2T molecules present against the number of molecules neutralized, or:
where n = molecules of H2T neutralized per molecule of acidity reducer Solving for the amount of acid reducer we get:
Based on equation 12 above, FermCalc calculates the following addition rates to reduce acidity by 0.1% (1 g/l) tartaric.
For additional information on using these additives, see this article by Bill Collings. Back to top
© 2007-2010 Steve Gross |
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