If there are still a few grams of residual sugar, light sulphiting at 1g/hL can be applied to temporarily block the growth of lactic acid bacteria, thereby providing the time necessary for the yeast to break down the sugars. The risks of deviation are then minimal.
This depends on the winemaker's objectives. If clarification is desired, a lower temperature is recommended to favour precipitation. If a quick start to malolactic fermentation is preferred, a higher temperature of 20°C is more appropriate.
Micro-oxygenation consists of adding a certain amount of oxygen to the wine in a controlled manner which helps improve colour, structure and aromas. A steady supply of oxygen is the objective, but the rate of supply should always be lower than the wine's consumption rate so that there is no accumulation of oxygen in the environment. The benefits include:
Increase in colour intensity. The oxygen supply creates ethanal molecules that enable tannin-anthocyanin bonds. This compound combination is stable over time, thereby preserving colour intensity in the long term.
Reduced perception of vegetal notes. Although micro-oxygenation does not reduce the quantity of IBMP present in the wine, it does have a "masking effect" on the wine's vegetal notes.
Softening of tannins and increased body/richness. This technique reduces the reactivity of tannins that are perceived as rustic during tasting. The reactive (or green) tannins are replaced by firm (harder) tannins. The perception of richness is increased, giving the wine a fuller, "coated" character.
If the vat needs to improve one of the three criteria mentioned above, micro-oxygenation may be appropriate. Tasting and the final wine profile are the key tools when deciding whether or not to apply micro-oxygenation.
Sulphites that will combine with ethanal. It is therefore necessary to carry out micro-oxygenation prior to sulphiting. There is however an exception. When micro-oxygenation is required between AF and MLF, with a sulphur addition at 1 g/hL slows down bacteria development without affecting micro-oxygenation, since there is only a very low presence of sulphites.
Turbidity also impacts micro-oxygenation efficiency because the lees will consume the oxygen provided. A low turbidity (<300 NTU) is necessary for successful micro-oxygenation.
Temperature impacts the oxygen dissolution in the wine. It is therefore important to ensure that the temperature is not too low. If oxygen is added to a wine that is too cold, it may accumulate and cause oxidative problems. The optimal temperature is between 16 and 18°C. Note that an excessively high temperature can trigger the start of MLF.
Maximum oxygen flow rate in relation to temperature (source: Vivelys)
There are several criteria when it comes to monitoring micro-oxygenation. The two critical aspects to monitor are:
The amount of dissolved oxygen. If an accumulation of oxygen starts to be observed, it means that the wine is not using all the oxygen that is being supplied, so this should be reduced or even stopped.
The taste of the wine, especially regarding ethanal perception. Ethanal evokes various aromatic notes depending on its concentration, ranging from light chocolate to mustiness.
Colourimetric monitoring is also possible, in particular by tracking the bluish tint evolution to measure the beneficial aspects of micro-oxygenation on the colour.