The other day I received a notice from the traffic department, a speeding fine. I required a large glass of wine before opening it, but fortunately not too bad…. However, did you know that fining often also takes place when wine is made? No, I am not referring here to a disciplinary action, but rather to a winemaking step or intervention.
Wine fining refers to the practice of adding something to a wine (called a fining agent) that removes something else from the wines. The fining agent can be in a liquid or solid form and basically binds to certain compounds when added to the wine and let it settle down to the bottom of the tank due to gravity. Now why would one like to remove stuff from wine? Rather drink it one would think… Winemakers sometimes use fining to clarify wine, to remove unwanted aromas of other compounds that can cause instability in the wine at a later stage, or soften the taste of the wine.
Wine fining agents can be classified according to what they remove in wine or what they consist of. One of the most commonly used fining agent in especially white wine is called bentonite. This is a type of clay that is added to white wines to remove proteins and to clarify the wines. These proteins originate from the grapes and can cause turbidity in the wine after bottling. At wine pH these proteins have a positive charge and the bentonite a nett negative charge. We all know that opposites attract and the bentonite basically binds to the proteins and it settles out to the bottom of the tank. After a week or two the winemaker can then rack the wine from the so called settling lees (the latter contains the settled proteins bound to the bentonite) and thus separate it from the wine. Do not ask me how a clay ended up being used in winemaking, but bentonite is used in a number of other industries as well. It is imperative that the winemaker first do a trail to assess what is the minimum amount of bentonite required to remove most of the proteins, if too much bentonite is added the wine can be stripped of some of its aroma compounds, while more wine is also lost in the process, while too little bentonite will not do the trick.
Proteins fining agents are also often used, especially in red wine making. These actually consist of proteins and have a positive charge at wine pH. Rembert that these proteins are not the same as those originating from the grapes. Protein fining agents are normally used to remove too much tannins or other phenolic compounds from wine, as the protein bind to the tannins. Ox blood has been used in the past as a protein fining agent, but for obvious reasons this practice has been discontinued. Egg white, containing egg albumin, is a very old fining agent (already used in the times of the Romans). Gelatin and casein are also used, the former is normally produced from animal hides and the latter from milk. Nowadays proteins originating from potatoes, rice and soy are also being or in the process of being approved for usage for wine customers who are vegan. These protein based fining agents thus binds to tannins in red wines, or oxidised phenolics in white wines, and lower their levels in the wine.
Figure 1: Red wine on the left without gelatin, the one on the right has been fined with gelatin. The settling lees can be seen at the bottom of the container.
Other fining agents include activated carbon and PVPP. Carbon is normally used with caution, as it can easily strip a lot of flavour and colour from wine (hence the reason why it is used in aquariums due to its strong affinity to bind stuff). PVPP is mostly used to prevent white wines from becoming pink (more on this strange phenomena at a later stage!).
Factors that affects the efficacy of wine fining is the temperature of the wine, how well the fining agent is mixed with the wine, the clarity of the wine and how the wine was made. There are also a number of other fining agents available to the wine producer which I will not touch on now, but it is important to realize that most fining agent are not necessarily always added to wine. The wine maker must decide if a wine needs to be fined, as it adds extra costs to the process. Some wines come on the market that has not been fined at all. Coming back to fines, I’ll have to keep a better eye on my speedometer in future (-;