Calculation Methods for Winemaking Adjustments
©Copyright Ben Rotter 2005-2008
The ability to calculate accurate adjustments in winemaking empowers the winemaker to meet precise goals. This is of increased importance when a winemaker wishes to control certain winemaking parameters. Some winemakers are, however, daunted by the mathematics this might involve. The following article outlines simple mathematical approaches to common winemaking adjustments.
It is often required that a must or wine be chaptalised (i.e., have sugar added to it). As sugar is added to a must/wine, the volume of the must/wine changes due to the addition. This volumetric increase can significantly off-set the concentration of sugar in the liquid. Thus, when calculating sugar additions to meet a target sugar concentration, both the quantity of the addition and the volume change should be taken into account. The following calculation assumes that the addition of 1600 g of sugar to must/wine raises the volume by 1 litre. This value has proved to be relatively accurate in practise.
The amount of sugar, A, to add to a must of volume, Vi, and sugar content, Si, is equal to:
A = the quantity of sugar to add to the must [g]
Vi = the initial volume of must [L]
Si = the initial sugar concentration in the must [g/l]
Sf = the desired (final) sugar concentration in the must [g/l]
b = number of grams of sugar required to raise volume by 1 litre [g] = 1600
Note: the b factor here has been determined from a number of winemaking sources and, whilst volume changes due to sugar additions are not strictly linear, the value of 1600 is relatively accurate for use over a wide range of typical sugar additions in winemaking.
Following the addition, the final volume of must, Vf, will be approximately:
For example, the SG of the must is 1.030. From the table (first table under Hydrometer/Sugar/Alcohol Tables) this is approximately equivalent to 83 g/l of dissolved sugar. It is desired to take the must to SG 1.090, which is approximately equivalent to 242 g/l of dissolved sugar. The volume of the must is 12 litres.
Using the second equation above, the quantity of sugar required to make this SG rise is:
Thus, 2248 grams of sugar are required to make this SG rise. The must volume after this addition has been made will be:
Thus, when the SG has been raised to 1.090 with the addition of 2248 g sugar, the new volume of the must will be 13.4 litres.
Inverse Stock Solution Make-up Calculation
Sometimes a winemaker wishes to make up a stock solution such that a specific volume of stock solution will result in a particular increase of a compound in a given volume of must/wine.
The total stock solution volume will be T (ml). It is desired that the stock solution will deliver D (mg/l) of compound when S (ml) of this stock solution is added to V (litres) of must/wine. The stock solution is made by weighing out Q (mg) of compound and adding water to volume T, where Q is:
For example, it is desired that bentonite be added to a must/wine at a rate of 20 mg/l when 5 ml of 500 ml bentonite slurry solution is added to a 30 L volume.
T = 500 ml
V = 30 L
D = 20 mg/l
S = 5 ml
To make the solution, weigh out 60 g of bentonite and make up the volume to 500 ml with water. A 5 ml dose of this slurry will add 20 mg/l bentonite to a 30 L volume of must/wine.
Wine A has an abv/TA of Ca, and wine B has an abv/TA of Cb. It is desired to add wine B to wine A to achieve an abv/TA of Ct. Wine A has a volume Va and wine B has a volume Vb. What volume (V) of wine B is required to be added to the total volume Va of wine A to achieve this?
This can be used for alcohol or TA. Note that this is not applicable to pH due to the impact of buffering compounds in wine.
For example, wine A has a TA of 4 g/l and wine B has a TA of 10 g/l. It is desired to add enough of wine B to wine A to obtain a TA of 6 g/l. There is 20 L of wine A.
Thus, 34 L of wine B must be added to the 25 L of wine A to obtain the desired TA of 6 g/l in the blended wine.