After watching Stephane’s last video on how to make a beef consommé, I thought this week could be interesting to talk a bit about wine clarification. If you think about it, is it not strange that a fermented grape juice turns into perfectly crystal clear liquid? If I squeeze an orange and I make a glass of orange juice, the result is anything but clear. It is cloudy and there is pulp floating around, but if you pour yourself a glass of wine (especially a white) you can always see through it. Let us start from the beginning. Once the grapes have been harvested and brought to the winery, they get processed in different ways depending on what type of wine is being produced and then fermented. During this phase basically, the sugar contained in the grape juice get transformed in alcohol, CO2 and heat by the yeast. As you can imagine this process leaves behind many different byproducts. A lot of them are left in the fermentation vessel when the fermented wine is transferred to the next phase, but a lot of them stay in the wine. Again, think about your fresh squeezed orange juice. A lot of the pulp will stick to the tool that you are using to squeeze the orange, but a small part will get into the glass you are pouring it into. At this point depending on the process we might be looking at some more aging in which case again part of the byproducts of the fermentation will fall to the bottom of the vessel leaving most of the wine less cloudy, but still not completely clear. How do we get to that crystal clear result then? There are many techniques, but we can basically summarize them in three groups:
Fining is the process where a substance (fining agent) is added to the wine to create a bond with the unwanted suspended particles in order to create larger particles. Gravity will make these bigger and heavier particles fall at the bottom of the vessel more readily allowing the fined wine to be removed from the vessel leaving the sediment at the bottom. Unlike filtration, which can only remove a certain size elements such as dead yeast cells and grape fragments, fining can remove soluble substances such as tannins and proteins; proteins can cause haziness and tannins can increase astringency. Many substances have historically been used as fining agents and egg whites is one of the many examples. It is important to mention that even if the fining agent is added to the wine, it will not affect the flavor of the wine because once it bonds to the particles and falls to the bottom of the vessel it will be left behind. This also explains why not all wines are vegan or vegetarian friendly.
While fining clarifies wine by binding the fining agent added to the wine to suspended particles and precipitating them out as larger particles, filtration is achieved by passing the wine through one or more filters that capture particles larger than the filter’s holes.
This is the less obvious of the processes but it is also often used in order to achieve consistency since wines are shipped across the globe. Once bottled, a wine may be exposed to extremes of temperature and humidity, as well as violent movement during transportation and storage. This may cause cloudiness, sedimentation, the formation of tartrate crystals and ultimately, it may also cause spoilage. In order to avoid these problems, a lot of producers decide to expose the wine to extreme temperatures (hot or cold) in order to encourage the formation of crystals or to kill yeast and bacteria before bottling. The basic idea behind this process is to guarantee the freshness of the product regardless of where and when it will be opened.