** Alcohol Determination for Fortification ** -

- When producing sweet fortified wines the fermentation has to be arrested at a specific time by the addition of alcoholic spirit to prevent the yeast fermenting the wine to dryness.

- The timing and volume of the alcoholic spirit is critical to achieve the final desired alcoholic strength and sugar concentration.

- To calculate the timing of the fortification the formula below can be used.

X = 0.33S + 1.262W - 0.262G

Where -

X = is the sugar level or^{o}Bé of the fermenting must when fortification is required.

S = the final desired alcoholic strength (%v/v) of the wine after fortification.

W = the final desired sugar level or^{o}Bé of the fortified wine.

G = the initial sugar level or^{o}Bé of the grapes used.

To understand this formula lets run through the following example.

- The volume of spirit required can be calculated by applying the calculations below based on the Pearson's-square.

- X = V(C - A) / B - C

Where -

X = the volume of fortifying spirit required in liters (? L)

V = the volume of must or wine to Bé fortified litres (678 L)

C = the final alcohol content aimed for (18.0%v/v)

A = the required alcohol content of the fermenting wine at fortification (4.32%v/v - calculated above)

B = the alcoholic strength of the fortifying spirit (95%v/v)

Therefore -

X = 678 L (18.0 - 4.32) / 95.0 - 18 = 120 L

Therefore 120L of 95%v/v alcoholic spirit has to be added.

Final volume of wine is 678 L+ 120.5 L = 798 L

- Assume -

- First we need to realise that the final 4.0
^{o}Bé required, does not reflect the true final^{o}Bé or sugar concentration as would be determined for a sugar/water solution, due to the presence of alcohol.

This is because alcohol has a lower density than water and will obscure the 'true'^{o}Bé by 0.262^{o}Be/1 %v/v of alcohol.

i.e. 18%v/v * 0.262^{o}Bé / 1%v/v = 4.68^{o}Be (obscuration).

or obscuration =**S*** 0.262

therefore the final true Baumé or sugar concentration of the fortified wine will be 4.0 + 4.68 = 8.68^{o}Be.

or final true^{o}Bé = 0.262**S**+**W**

The initial 13.0^{o}Bé minus final 8.68^{o}Bé is 4.32^{o}Bé (13.0 - 8.68 = 4.32)

i.e.**G**- (0.262**S**+**W**)

Therefore the wine should be arrested by fortification after 4.32^{o}Bé has been fermented to alcohol to leave 8.68^{o}Bé of sugar.

The formation of 4.32 %v/v alcohol, (@ 1%v/v alcohol/1^{o}Bé), will obscure the true Bé of 8.68^{o}Bé by -

4.32%v/v * 0.262^{o}Bé / 1%v/v = 1.12^{o}Bé obscuration

i.e. (**G**- 0.262**S**+**W**) * 0.262

Therefore the Be to fortify at is the true Bé - the obscured Bé

i.e. 8.68^{o}Bé - 1.12^{o}Bé = 7.56^{o}Bé

i.e. (0.262**S**+**W**) - 0.262(**G**- 0.262**S**+**W**)

i.e. 0.262**S**+**W**- 0.262**G**- 0.068**S**+ 0.262**W**

i.e.__0.33__**S**+ 1.262**W**- 0.262**G**

i.e 0.33 * 18 + 1.262 * 4.0 - 0.262 * 13

= 7.56^{o}Bé

- The Pearson's Square can be use to calculate the volume of alcohol that needs to added to a solution (must/wine) to achieve the desired final alcoholic strength.

A | B | |||

\ | / | |||

X | ||||

/ | \ | |||

C | D |

Where -

X = is the final desired alcohol concentration (18.0%v/v)

A = alcohol concentration (%v/v) of the must/wine to be fortified (4.32 %v/v)

C = the alcoholic strength/concentration of the fortifying spirit (95.0%v/v)

D = the difference between X and A (18.0 - 4.32 = 13.68)

B = the difference between C and X (95.0 - 18.0 = 77.0)

4.32 | 77.0 | |||

\ | / | |||

18.0 | ||||

/ | \ | |||

95.0 | 13.68 |

Then the volume ratio of the fortifying spirit to must/wine = B/D = 77.0/13.68 = 5.63 = 1/5.63

i.e. for 678 L of must/wine add 678L * 1/5.63 = 120L

i.e. 120L of 96%v/v fortifying spirit will need to be added to 678L of must/wine, (@ 4.32%v/v alc.), to finish with a fortified wine of 18%v/v alcohol.