Winegrowers Supplies - Enrichment (Chaptalisation) of grape must
At the outset it is necessary to define the terms/jargon used to describe alcohol:-
Prior to fermentation: total alcohol = natural alcohol plus
potential alcohol arising from enrichment by adding sugar (or rectified concentrated grape must).
In fermented or bottled wine: total alcohol = actual
alcohol plus potential alcohol content of any unfermented sugars.
Natural alcohol is the %vol that would be produced by fermentation of the
juice/must if no enrichment were to take place. In Germany
this is called 'available alcohol' which I think is a better term.
Under European Comission regulations applying to the United Kingdom the minimum permitted natural alcoholic strength of a must is 5 %vol (44 °Oechsle) for Table Wines, or 6 %vol
(50 °Oechsle) for Regional (Table) Wines and Quality Wines. Other countries have higher levels for Quality Wine.
I believe that the level for United Kingdom Quality Wine should be raised to 60 °Oechsle (7.7 %vol).
°Oechsle is simply specific gravity minus 1, then multiplied by 1000.
Actual alcohol is the %vol of the wine (in tank or bottle), measured by analytical techniques. This will be lower than total alcohol according to the amount of residual sugar in the wine.
For example: if the natural alcohol is 9.1 %vol and this must/juice is enriched by 2.3 %vol the total alcohol is 11.4 %vol; if the wine does not
fully ferment out the actual alcohol will be slightly less than 11.4 %vol but the total alcoholic strength will still be 11.4 %vol.
Subsequently, if you add Süss-reserve at 11.4 %vol total alcoholic strength (84 °Oe) this 'dilution' will reduce the
actual alcohol %vol but not the total alcohol; if the Süss-reserve is less than 84 °Oe then the total alcoholic strength will be reduced very slightly.
Regulations state that the actual alcoholic strength by volume (%vol) of wine in bottle shall be at lowest 8.5 %vol and not more than 15.0 %vol.
1) Firstly it is necessary to measure the temperature-corrected natural alcoholic strength of the must in °Oechsle (or Brix) at 20 °C, with a refractometer or hydrometer.
You can then look up the alcohol %vol in the UK Wine Standards Branch table; however, WSB figures are inaccurate (especially above 94 °Oe)
so I have added (in brackets) accurate figures from German tables:-
°Oechsle = alcohol %vol = Sugar g/l = % mas Sacch = Brix
44 5.1 (5.13)
87 10.94
45 5.3 (5.29)
90 11.18
46 5.5 (5.45)
92 11.42
47 5.6 (5.61)
95 11.66
48 5.8 (5.76)
98 11.90
49 5.9 (5.92)
100 12.14
50 6.0 (6.08)
103 12.37
51 6.2 (6.24)
106 12.61
52 6.4 (6.39)
108 12.85
53 6.6 (6.55)
111 13.08
54 6.7 (6.70)
114 13.32
55 6.9 (6.86)
116 13.55
56 7.0 (7.02)
119 13.79
57 7.2 (7.17)
122 14.02
58 7.3 (7.33)
124 14.26
59 7.5 (7.49)
127 14.49
60 7.7 (7.65)
130 14.72
61 7.8 (7.81)
132 14.96
62 8.0 (7.96)
135 15.19
63 8.1 (8.12)
138 15.42
64 8.3 (8.27)
140 15.65
65 8.4 (8.43)
143 15.88
66 8.6 (8.59)
146 16.11
67 8.7 (8.74)
148 16.34
68 8.9 (8.90)
151 16.57
69 9.1 (9.06)
154 16.80
70 9.2 (9.22)
156 17.03
71 9.4 (9.37)
159 17.26
72 9.5 (9.53)
162 17.49
73 9.7 (9.69)
164 17.72
74 9.8 (9.84)
167 17.95
75 10.0 (10.00)
170 18.18
76 10.2 (10.16)
172 18.40
77 10.3 (10.31)
175 18.63
78 10.5 (10.47)
178 18.86
79 10.6 (10.63)
180 19.08
80 10.8 (10.79)
183 19.31
81 10.9 (10.94)
186 19.53
82 11.1 (11.10)
188 19.76
83 11.3 (11.26)
191 19.98
84 11.4 (11.41)
193 20.21
85 11.6 (11.57)
196 20.43
86 11.7 (11.73)
199 20.65
87 11.9 (11.88)
201 20.88
88 12.0 (12.04)
204 21.10
89 12.2 (12.20)
207 21.32
90 12.4 (12.35)
209 21.54
91 12.5 (12.51)
212 21.77
92 12.7 (12.67)
215 21.99
93 12.8 (12.83)
217 22.21
94 13.0 (12.98)
220 22.43
95 13.0 (13.14)
223 22.65
96 13.1 (13.30)
225 22.87
97 13.3 (13.45)
228 23.09
98 13.4 (13.61)
231 23.31
99 13.6 (13.76)
233 23.53
100 13.8 (13.92)
236 23.75
101 13.9 (14.08)
239 23.96
102 14.1 (14.24)
241 24.18
103 14.2 (14.40)
244 24.40
104 14.4 (14.55)
247 24.62
105 14.5 (14.71)
249 24.83
106 14.7 (14.87)
252 25.05
107 14.8 (15.02)
255 25.27
108 15.0 (15.18)
257 25.48
109 15.2 (15.33)
260 25.70
110 15.3 (15.49)
263 25.91
2) Decide on the total alcoholic strength of the enriched must, according to the type of wine you are making. The maximum enrichment allowed (from 2009 harvest onwards) is 3.0 %vol; unless a formal Request to increase the limit to 3.5 %vol is approved.
For Sparkling wine, I aim for 10.5 %vol, as the secondary fermentation will add a further 1.5 %vol.
For dry white wine, I aim for 10.5 or 11.0 %vol, according to the vine variety.
For medium-dry or medium white wine, I aim for 11.5 %vol (the maximum permitted for enriched white wine), since this will be reduced later by the addition of Süss-reserve before bottling.
For rosé, I aim for 11.5 or 12.0 %vol (the maximum permitted for enriched rosé wine).
For red wine, I aim for 12.0 %vol (the maximum permitted for enriched red wine).
3) Calculate the weight of dry sugar required to achieve the desired total alcoholic strength; water may not be added to dissolve the sugar. Concentrated grape must or rectified concentrated grape must can also be used, but normally these are not used in UK.
Beet sugar or cane sugar may be used, beet sugar contains less pectin so is more likely to give a protein haze. Beet sugar is cheaper and hence is normally used, although cane sugar has more flavour.
a) For white wine or rosé, Wine Standards Board's figure of 16.5 grams of sugar per litre of must, to produce 1 % alcohol by
volume, is slightly low; they admit it is conservative. German data is 16.85 g/l, Australia (according to Bryce Rankine) is 16.95 g/l
and France (according to Peynaud) is 17 g/l.
According to Peynaud, cane sugar was used exclusively for white wines, although I doubt it is used in France today. The land around Champagne is a major sugar beet growing area.
Hence, for white wine or rosé: total grams of sugar to be added =
total litres of must x (desired total alc %vol - natural alc %vol) x 16.85 g/l
Enrichment by 3.0 %vol (the maximum normally allowed) is achieved with 50.55 grams of sugar per litre of must.
It is essential to rouse continuously while sugar is being added, else the sugar will form a solid lump on the tank bottom.
b) For red wine, which is generally fermented at a higher temperature, 19 (according to Bryce Rankine) or 20 (according to Peynaud) grams of sugar per litre
is needed to produce 1% alcohol by volume, because of loss of alcohol by evaporation during pumping over of the warm wine. It is the free-run wine that is
most enriched; the press wine more or less keeps its initial strength. According to Peynaud, there is no distinction made between using beet or cane
sugar for red wines.
Discussion in the UK has concluded that about 18.3 grams of sugar per litre of must, should be added in order to produce 1% alcohol by volume.
Hence, for red wine: total grams of sugar to be added =
total litres of mash x forecast %-extraction x (12.0 alc %vol - natural alc %vol) x 18.3
Forecasting the %-extraction (% of must/juice that will eventually be pressed out from the de-stalked mash) is not easy and relies on experience.
Each variety and vintage year is slightly different, according to the juiciness of the particular grapes. In my vineyard with the varieties Pinot
Noir, Rondo, Regent, Dornfelder and Dunkelfelder, the overall average has been 83.3%, but individual wines have varied from 77 % (small dry berries)
to 89 % (large juicy berries):-
Pinot Noir (thin skins): from 82 % to 89 %, average 84.5 %
Rondo is the most consistent: from 81.5 % to 84.5 %, average 83 %
Regent/Dunkelfelder: from 77 % to 86.5 %, average 82.5 %
Dornfelder: from 80 % to 89 %, average 83.5 %
This constitutes a possible error in enrichment of up to +-0.23 %vol.
Because red wine is fermented 'on the skins' it is not possible to use a rouser in the tank to dissolve the sugar, so an alternative method has to be used:-
- if an open-top tank is being used, the sugar can be added gradually day-by-day, simply tipping some on to the top of the mash just before the skin-cap is pushed down.
- or the technique of 'pumping over' can be employed. The sugar needed is tipped little by little into a small container fed by must from the tank. The resulting syrup is
stirred continuously and pumped back to the top of the tank over the skin-cap.
This is usually done in one step at the beginning of fermentation when the fermenting must is starting to get warm and the pomace cap is just forming.
Sugar dissolves more easily in warm must.
Other sources of error in the enrichment process:-
1) Measurement of the volume of must:-
The % error for every 1 mm error in measurement of height in a vertical cylindrical tank = 1 divided by the height in mm; eg. for 1000 mm high must the error is 0.1 %. The diameter of the tank is less significant.
For tanks that do not have a flat base there is the additional problem of allowing for this.
The temperature of the must can lead to volume calculation errors.
A must that is not completely settled will contain suspended solids which will contribute a small volume calculation error, as would sludge in the bottom of the tank.
2) Initial measurement of grape-sugar (natural alcoholic strength):-
There are several methods of measuring the sugar content of a liquid, all require a representative, homogenous sample.
A hydrometer reading is affected by the temperature of the must and by the presence of material other than glucose/fructose in the must (which would increase the apparent must weight). The temperature effect can be eliminated by the use of a water bath, at 20 °C, to maintain a constant temperature for the measurements.
A refractometer reading is affected by the temperature of the must and by the presence of material other than glucose/fructose in the must (which could either increase or decrease the refractive index of the must and therefore give an apparent must weight that was higher or lower than the actual). The temperature effect is compensated for by a adding or subtracting a correction factor according to the measured temperature. The latest refractometers have built-in automatic temperature compensation.
Chemical analysis for reducing sugars is affected by other substances that reduce CuII to CuI (this would have the effect of increasing the apparent must weight). The analysis technique is straightforward.
Enzymic methods are affected by other substances that react with the enzyme or interfere with its action (leading to an apparent must weight that was higher or lower than the actual).
The only really accurate method, of determining sugars in grape must, is liquid chromatography. Here glucose and fructose are separated from other sugars, and from other compounds, in a liquid chromatography apparatus. This apparatus is prohibitively expensive to buy or operate.
3) Sugar addition:-
The scales used to weigh out the sugar may be inaccurate, leading to too little or too much alcohol being produced.
The sugar may not completely dissolve in the must, settling out in the sludge at the bottom of the tank, leading to too little alcohol being produced.
The types of sugar used for enrichment (granulated beet sugar, cane sugar, rectified concentrated grape must) will produce slightly different amounts of alcohol.
4) Natural variations in the fermentation:-
C6H12O6 = 2 C2H5OH + 2 CO2
Glucose/fructose = ethanol (ethyl alcohol) + carbon dioxide. 180 g = 2 x 46 g + 2 x 44 g
So, theoretically, 180 grams fructose/glucose = 92 grams alcohol
Similarly, 2.04 g sugar gives 1 g carbon dioxide (0.51 litres) at 20 °C.