Once the wines have all been blended together, the resultant blend is chilled at around -4°C. This stabilises the wine through inducing the crystallisation of tartaric acid in a controlled environment so it doesn’t occur in bottle while ageing. The wine is held at this low temperature for at least a week (often longer), or if the process needs speeding up cream of tartar crystals are used. The process of renewed clarification then leaves the wine perfectly clear.
If a wine is bottled while unstable, the wine is at risk if exposed to cool temperatures (even as little as having the bottle in the fridge to chill before serving), this can trigger crystallisation from the reaction between potassium and tartaric acids. While it is undesirable to have solids within your wine, it is the shift in pH levels that gives a greater impact on your tastebuds, and if gone unnoticed the wine would taste out of balance.
With the grapes crushed into juice, and now the juice fermented into wine, there are still a few more steps which a winemaker can choose to take. Fining and filtration are treatments that further refine the wine to be more appealing to the wine drinker.
The first step is to add an agent into the barrels of wine that binds itself to certain targets, such as tannins and proteins. This creates a precipitate of unwanted elements that are then removed through another racking. It is recommended to only use a fining agent in the smallest doses as too much can cause a loss of flavour and complexity in the wine. The fining process is often used by red wine producers to take away the last few harsh and astringent elements within the wine and clarify it to a nice clear red liquid.
As wine is a complex structure not all fining agents work the same, leaving the winemaker to make an important decision on which agent to use for each wine.
Types of Agents:
These agents physically remove the unwanted elements from the wine.
Egg Whites - Containing the protein Albumen, egg whites are ideal for reducing harsh and astringent tannins while clearing the wine of other particles.
Gelatins - Specialised purified proteins, gelatin can be used to help clarify the wine while also reducing tannins to an extent.
Potassium Caseinate - a milk-derived protein used to soften a red wine’s tannin structure.
Rather than removing the elements, additive agents work to coat and add to the molecules that cause the harshness and tannins in wine. They are able to modify the characters rather than eliminating them all together, meaning it is less of a risk of stripping a wine of all its character.
Oenological tannins - used during the ageing period, they help develop the mid-palate structure and mouthfeel of wine. Best used to round out thin and aggressive wines, and adds a layer of protection against oxidation.
Opti Red/Booster Rouge - specially designed, yeast-derived protein fractions used to add body and mouthfeel to wine.
Similar to filtering coffee, the wine is then passed through a material with very small pores that only allow liquid and miniscule solids through. Why filter wine? Winemakers opt to perform this step to stabilise their wines further and improve the aesthetic of the wine in the glass. As a side effect, filtration also softens the edges of a wine. For wines without flaws, filtration is not necessary and is more a decision about how structured you want your wine. Wines with flaws such as residual sugar or Malic acid left in the wine, then filtration is the only way to guarantee microbial stability for the wine.
The size of filtration materials can vary depending on how many solids you wish to keep in your wine. Generally speaking the pores are between 0.45 and 5 microns. 2-micron filters are best for removing yeasts, while 0.45-micron filters are needed for the removal of bacteria.
Nominal vs Absolute
Nominal filters are generally cheaper and less effective by removing most but not all particles from the wine. Best for wines without flaws, where the winemaker just wishes to filter out most of the solids in the wine. Absolute filters are the top of the range products that ensure no particles make it past unless smaller than the pour size. They are ideal for flawed wines that need protection and stability before bottling.
Cartridges vs Pads
There are two different forms of filtration materials; cartridges and pads. Cartridges are more expensive but come with their own housing and are able to be reused several times through. Contrastingly pads need both a plate and frame for the set up and are single use products. While pads are more messy to work with there is the ability to discard them straight away rather than the cleaning process that must be done for the reusable cartridges.
Finally, once the wine is at its peak and the winemaker is happy with their product, the process of putting the wine into glass bottles begins.
Bottles are washed and corks prepared for the (often mechanised) process of pouring wine into bottles and pressing the cork to seal it. To prevent as much oxidation as possible, the process must be seamless with no splashing of wine when being poured. Filled to about a centimetre below the position of the base of the cork, this ensures minimum aeration for any range of cellaring. A cork is then promptly pressed into the neck of the bottle to seal it up. The bottle must then be left standing upright for a few days as the cork expands to the full size of the neck and pressure normalises in the bottle, so when it is laid down on its side there is no leakage. The winemaker can then choose to place a seal over the cork either with wax, a foil, or some other form of branding that suits the wine label.