Winegrowers Supplies  -  Making White Wine - from concentrated grape juice

1) Diluting the concentrated juice:

    For white wine I suggest aiming for:-
         11.4% alcohol = 84 °Oeschle juice (specific gravity 1.084) = 20.2 Brix

The concentrate may not be exactly 65 Brix, it could be up to 68% Brix, so:-

Pump good-tasting fresh water into the tank until it is 62% full. For concentrate at 65 Brix, 2.215 parts water to 1 part concentrate would give 20.2 Brix.

Start the tank-rouser running.

Use a Fork Lift Truck, with a rotary drum fitting, to lift a drum above an open top variable-capacity tank and slowly tip the concentrated grape juice into the water. Add more drums until the tank is about 90% full, empty the drums completely.
Note: finally there will need to be at least a 50mm air space at the top of the tank, between the juice surface and the lid, to accomodate the fermentation foam. This is about 2% of the tank volume.

Measure the specific gravity (°Oechsle) of the diluted juice, with a refractometer.
Record the volume of diluted juice in the tank.
Calculate how much more water needs to be added to reduce the specific gravity to the intended 84 °Oe. Add this amount of water and re-measure and adjust until correct.

Take a sample of the diluted juice and measure the level of free SO2.
Add wine sulphur to raise the free SO2 to 20 mgm/litre.

Switch the rouser off but leave it in the tank.

2) Preparing the juice for fermentation:-

a) Prepare bentonite; for removing any excess protein.

b) Measure the acidity of the juice with a test such as the Sulfacor.

    Calculate the amount of citric acid to adjust the acidity to 8.0 g/l.
    Turn the rouser on again and add the acid crystals to the top of the tank, so that they are dissolved in the juice.

c) Add the bentonite suspension, after draining off excess water, and rouse in.

d) Add yeast nutrients (should be added before the addition of the yeast) and rouse in.

e) Rehydrate the selected yeast (Oenoferm Klosterneuberg); rehydration procedure.
    Add to the must, rouse in, then switch off the rouser and remove it from the tank.

f) With the cooling plates fitted to the lid, lower it into the tank so that it is about 50 mm above the surface of the juice. Pump up the sealing tube to 0.5 bar so that the lid is supported.

Leave the juice to ferment. Monitor the temperature regularly, it should be at least 15 °C initially. When the fermentation starts and the temperature rises, run cooling liquid through the cooling plates, adjust the speed of flow to keep the temperature at about 10 °C.

The cooling liquid can be cold water. For a more efficient method then a closed circuit system using a glycol (antifreeze) solution recycled through a heat exchanger, enables the water-mixture to be cooled to a much lower temperature. A low speed pump is needed for circulation, with controllable flow rate to enable the temperature of the fermenting wine to be adjusted.

3) After the fermentation is complete: lower the lid of the variable-capacity tank so that it floats on the wine.

4) First racking: normally it takes about 4 weeks after the end of fermentation for the dead yeast to settle; however, this can be speeded up by chilling the wine to about 2 °C, in which case a few days at this temperature should be enough. This will also help to achieve tartrate stability (excess tartrate will precipitate on the walls of the tank). After this the wine can be 'racked' (pumped) off from the sediment.

    Normally racking is carried out through the flap-valve. If a tank is without a man-way door it is possible to rack off through the bottom outlet of the tank, although this is not normal practice; if the yeast-lees are compact enough only a small amount of lees is carried through. The first litre or so can be run off into a large jug or bucket, the juice from this can then be poured into the receiving tank leaving the solid sediment to be  discarded. Pump into the bottom inlet of the receiving tank (clean and sterile); put the floating lid inside (with pneumatic seal deflated, and cooling tubes removed) so that it rides up with the wine.

    To minimise the aeration which occurs when racking; make sure there is no leak on the suction side of the pump. The colder the temperature the more oxygen the wine can dissolve (leading eventually to greater oxidation). Each racking will reduce the ultimate quality of the wine, so plan to rack only the minimum number of times necessary.

    Before starting to pump, put into the receiving tank a calculated amount of wine sulphur; 7 grams per 100 litres of wine; providing up to 35 mg/l free SO2.

5) Every week: take a sample of the wine and measure the level of free SO2.

    If necessary add wine sulphur to raise the free SO2 to 35 mg/l.
Some grape varieties 'consume' free SO2 more quickly than others so need more frequent sampling and addition.

    In the first week, measure the acidity of the wine with the Sulfacor test.
Calculate the amount of citric acid to adjust the acidity to 7.0 g/l.
If any acid needs to be added, use the rouser and add the acid crystals to the top of the tank, so that they are dissolved in the juice.

6) Sterile Filter and Bottle:

    The wine usually needs rousing (for some hours) to remove excess CO2, unless you like spritzig/petillant wines. A small amount of Nitrogen gas can be squirted into the wine, with the lid off, but this would remove all of the CO2, which may not be desirable.

    Test for protein stability.

    Measure and adjust the free SO2 level so that it is 30 to 35 mg/l.

    To make off dry wines: if there are no legal regulations about the sweetening of the wine, it will be much cheaper to do this with some of the concentrated grape juice (rather than Süss-reserve), between 1% and 3% depending on the acidity chosen; carry out tastings at 0.5% intervals to ascertain the optimum % addition.
    Add the desired amount and rouse in well.
    Re-test for protein stability.

    Sterilise the bottles with 2% free SO2 solution, rinse with pure water afterwards.

    Filter and bottle.