The blending of wines is the mixing of different wines from different containers according to specifications (like alcohol and sugar concentrations) which were identified for different products. The processes of wine blending can be divided into different stages. Firstly, the quantities of the different wines must be calculated. The blend must then be mixed in small scale in the laboratory, where after it is evaluated and the necessary adjustments are made to the blend. Usually a fining (like gelatine or bentonite), which is also applied in small scale in the laboratory, is required. After the pilot blend has been approved, a work instruction will be compiled by the winemaker. The following particulars will be included in such work instruction
The number, wine description and quantity of wine which will be used from each tank.
The number and capacity of the receiving tank(s) where the wines will be mixed, as well as the cleaning process of these tanks, before it is used.
The sequence in which the different containers will be transferred to the receiving tank(s).
The expected wine quantities in the receiving tank(s).
Which pumps will be used for the transfer and whether the mixing will be done by pump overs or mixers.
Which samples must be drawn after the mixing for tasting and analysis (for example alcohol content, volatile acid concentration, sulphur dioxide concentration, acid concentration, sugar concentration and pH).
Adjustments after the analysis by adding for example acid and sulphur dioxide and mixing it properly with the wine.
Additions of fining agents (for example bentonite and gelatine) and how it must be prepared and mixed with the wine.
How (for example by rackings or filtration) the wine will be clarified after mixing, additions to be made, and to which tanks the clarified wines should be transferred.
Which samples should be drawn again for tasting and the necessary analytical purposes.
All these actions of the work instruction must also be documented and recorded.
After the work instruction has been received, preparations must be made to execute it and it is especially important to attend to the following:
Ensure that the container numbers, wine detail and volumes of the wines to be mixed are correct.
Taste the wines in the different tanks to ensure that they correspond with the details of the work instruction.
Control whether the volume capacity of the receiving tanks is sufficient to accommodate the wine and control whether these tanks are empty and clean and no equipment like lights, valves or gaskets were left inside.
Ensure that the tank covers of all tanks are open, before the pumping of the wine is commenced. If it is not done, the delivery tank can implode.
The delivery tank and receiving tank(s) can be connected by fixed pipelines or wine hoses which were cleaned beforehand. Wine hoses are usually fixed to the racking valve of the supply tank and the bottom valve of the receiving tank. The pump must be as close as possible to the supply tank, where it is fixed with a flexible hose to the racking valve. The hose must be long enough to bend into the doorway, if the wine is racked from lees.
If air contact needs to be avoided, the fixed pipelines, wine hoses and receiving tank(s) can be flushed with inert gasses like nitrogen, carbon dioxide (dry ice) or argon. This can be done by connecting the hoses to the pump, opening the bypass of the pump and flushing the line until inert gas has reached the end of it. The hose can then be connected to the bottom valve of the receiving tank to flush it also. It is preferable to put dry ice in both tanks while the wine is transferred.
To ensure that no leakage occurs and valves are open, it is advised to attach all the hoses, open the bypass of the pump and then without starting the pump, open the valve of the supply tank. The flow of the wine can consequently be followed and potential problems can be identified and solved.
If barrels need to be mixed, it is always better to evaluate it individually, before it is mixed.
Tank covers must be open before wine transfers. An imploded tank.
During the transfer of wines no leaks should occur and sound hoses and tight fittings must be used. Damaged parts of leaking hoses can host undesirable micro-organisms, which can spoil the wine. After the transfer action has been completed and the pump was switched off, all tank valves must be closed and the hoses loosened and drained. All equipment, containers and hoses must therefore be cleaned according to the cellar’s work instructions.