Bottling is the final process before a wine reaches the consumer. It is consequently of cardinal importance to execute it in such a way that the wine quality is not influenced negatively, but also that the right wine will be in the right market at the right stage. Seeing that it is a mechanical process with different physical inputs, its logistical planning is the core element of the process. Many cellars use mobile bottling nowadays, which applies more pressure on its orderly planning.
Depending on the applicable activity, the scheduling of wine bottling can be divided in different time frames:
Eight weeks to four months prior to bottling
The composition of the required blend is the first process that needs to be addressed prior to bottling. This will determine the style, for example the intensity of wood character and final basic analysis of the wine like alcohol, total acid, pH, volatile acidity and residual sugar concentrations. Apart from the influence of these concentrations on the sensory characteristics of the wine, it is also important regarding the compliance with legal and export requirements. Different stabilisation processes will also be determined by the final composition of the blend and it must be remembered that the mixing of different stable components will not necessarily lead to a stable blend of the components.
Six to eight weeks prior to bottling
If required, the macro-chemical and tannin wood profile adjustments of the blend must be made during this period.
Macro-chemical adjustments include especially alcohol, total acid, volatile acidity and sweetening adjustments. It can lead to pH-changes, which has an influence on the wine stability. Different tannin or alternative wood products in powder or liquid form can be used to adjust the structure or wood profile of the blend, but it must be done in time before the wine is stabilised.
Four to six weeks prior to bottling
Although protein and tartrate stability are the most important stability requirements, the colour and microbiological stability of wines must not be underestimated.
As result of the high tannin concentration of red wines they are usually protein stable. Protein unstable white and rosé wines can increase in temperature or over time become turbid as result of pH changes. A bentonite fining, followed by filtration is usually applied for the protein stability of white and rosé wines. The fining dosage must be determined by laboratory trials and care must be taken that the same bentonite is used for the laboratory trials as in the cellar. White and rosé wines are usually seen as protein stable when a sample shows a reading of two or less NTU after two hours at 80°C.
The tartrate (cold) stability of wines can be obtained and evaluated in different ways. The aim thereof is the visual absence of cream of tartar (potassium bitartrate) crystals in the wine. It is once again especially important in the case of white and rosé wines, because these wines are usually chilled before being drunk and lower temperatures facilitate the formation and precipitation of these crystals. Tartrate stability can be obtained by cooling, crystal seeding, electrodialysis or ways of inhibiting the crystal formation. The latter includes amongst others the addition of substances like mannoproteins, arabic gum or carboxymethylcellulose (CMC). Cooling and crystal seeding can, however, take up to three weeks and consume much energy as opposed to the use of CMC which is easy, but different precautionary actions must be adhered to. Different methods exist to determine the tartrate stability of wines, but an absolute standard does not exist and cellars will make individual decisions in this regard.
One to two weeks prior to bottling
The stable blend can be filtered in different ways prior to bottling. It can either include a diatomaceous earth-EK combination or a nominal 0.45 cross-flow filtration for clarification of the wine, before the final 0.45 micron membrane filtration in the bottling line. It is more difficult to filter cold wine seeing that the filtration flow rate decreases by 2% for each one °C drop in the wine temperature. Oxygen also dissolves much easier in colder wine and it is consequently recommended that wine is not bottled at lower than 15°C. In spite of a low NTU value, it can still be difficult to filter wine as result of dissolved pectins, beta-glucans and protein colloids. The treatment of wines with pectinase and beta-glucanase enzymes can prevent it.
48 to 72 hours prior to bottling
Final adjustments can still be made at this stage. It includes the addition of arabic gum for the improvement of the mouth-feel and colour stability. Certain mannoproteins can also be added to improve the mouth-feel and protect the colloidal and tartrate stability of the wine. It is important to use laboratory trials to determine the dosage of the additives, as well as to take note of the suppliers’ prescriptions, because filtration can be influenced thereby. Free sulphur dioxide analyses must be done and if necessary, the required adjustments must be done. If necessary the temperature of the wine must be increased to 15°C and the final dissolved oxygen and carbon dioxide concentrations must also be determined. Both can be decreased by nitrogen dosing. The recommended dissolved oxygen concentration prior to bottling is less than 1.0 ppm for red and less than 0.75 ppm for white wines and the dissolved carbon dioxide concentrations are less than 400 ppm for red and between 750 to 900 ppm for white wines respectively.
Final sulphur dioxide and gas adjustments can be made if necessary, before the final sensorial approval of the wine for bottling. It must also be ensured that the bottling pipelines and equipment do not contain any water.
The safest way to ensure that all actions have been executed and approved is the use of a comprehensive checklist as in Table 1. The example is not complete, but only a template, which can be comprehensively compiled by cellars.
Crowe, A., 2017. Checklist: Getting your wine ready for bottling day. Wine Business Monthly, June 2017: 27 – 33.