Alcohol Determination for Fortification

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Alcohol Determination for Fortification -

Introduction

Timing of Fortificatiom

Timing of Fortification - Example

Volume of Fortification Spirit Required

Pearson's Square

Introduction to 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.

Timing of fortification

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 ^oBé 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 ^oBé of the fortified wine.

G = the initial sugar level or ^oBé of the grapes used.

To understand this formula lets run through the following example.

Volume of alcoholic spirit required spirit

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

Timing of fortification - Example

Assume -
- we start with grapes with a sugar concentration of 13.0 ^oBaumé (G).
- and want to finish with a wine with -
  - a final alcoholic strength of 18%v/v (S)
  - and a sweetness level of 4.0 ^oBé as measured by hydrometry (W)
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' ^oBé by 0.262 ^oBe/1 %v/v of alcohol.

i.e. 18%v/v * 0.262^oBé / 1%v/v = 4.68 ^oBe (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 ^oBe.

or final true ^oBé = 0.262S + W

The initial 13.0^oBé minus final 8.68^oBé is 4.32^oBé (13.0 - 8.68 = 4.32)

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

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

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

4.32%v/v * 0.262^oBé / 1%v/v = 1.12 ^oBé obscuration

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

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

i.e. 8.68^oBé - 1.12^oBé = 7.56^oBé

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

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

i.e. 0.33S + 1.262W - 0.262G

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

= 7.56 ^oBé

Pearson's Square

A				B
	\		/
		X
	/		\
C				D

4.32				77.0
	\		/
		18.0
	/		\
95.0				13.68

Note: