Oxygen management of especially white wines is accepted by winemakers as common practice. Specific points in production dictate the amount of oxygen exposure that a wine could potentially endure and is managed in different ways to minimise the effects. After picking, en route to the cellar and during crushing are the times at which oxygen exposure reaches its peak. Incidentally, juice is also more readily oxidised than wine because enzymatic and not chemical oxidation is at play. From this point during the winemaking process oxygen uptake is supposed to decrease rapidly until only very small amounts of oxygen come in contact with wines, for instance during ageing or post-bottling (bottle ageing). During the bottling process, however, it has been found that macro oxygenation can, in some instances take place. More importantly this oxygen uptake during bottling can vary between bottles due to filler head differences.
Recent advances in oxygen measurement technology have contributed to quantify the level of oxygen exposure of each step of the wine production process, thus making it possible to investigate the role of oxygen in the shaping of a wine’s characteristics. The oxygen levels were determined using a NomaSenseTM oxygen analyser which is based on oxo-luminescence technology. This analyser is capable of measuring oxygen non-destructively in the dissolved phase and gas phase as well as through closed objects like a wine bottle. Key findings of relevance for oxygen management in the winemaking, bottling and preservation steps for South Africa and internationally is currently being researched.
White and red wines from South Africa were tested for dissolved oxygen (DO) and headspace oxygen (HS). DO in the holding tank, bottle and therefore also the pickup, HS oxygen of the bottles under screwcap and natural corks and the combination of the bottle DO and HS to form the total package oxygen (TPO) of a wine from a particular bottling line. It was found that TPO values varied between 0.7-7.5 mg/L, with head space oxygen being dominant.
Materials and Methods
Nomasense oxygen analysing equipment
NomaSense oxygen measurements are based on oxo-luminescence technology; this is a non-invasive, non-destructive and ready to use system. A blue light (high in energy) is transmitted towards a sensor spot which is in contact with the liquid or gas that is to be measured. This light excites the particles which in turn collide with oxygen. Red light (lesser energy) is transmitted back to back at the analyser. The difference in this energy between the two lights is correlated to the amount of oxygen in the liquid or gas that is measured.
The NomaSense oxygen analyser consists of a console and a selection of two probes. The dipping probe and the sensor probe. The dipping probe can be used in any liquid while the sensor probe is used to read sensor spots through any clear surfaces to quantify the oxygen content. Sensor spots are placed in positions where measurements are desired prior to the use thereof.