Once the wine is in tank, and the headspace is gassed with Argon (to displace any residual oxygen) it is time to take a sample of the wine to test its final chemistry. The chemistry analysis will determine whether there is any remaining bacteria in the wine that can cause flaws or faults in the wine. At this point we will be able to make decisions as to whether or not the wine needs to be fined or filtered before bottling. Fining is the process of clarifying a wine, removing any micro solids, bacteria, yeast and polyphenols (i.e. harsh tannins). A traditional fining solution would be egg whites. Today there are also other gelatins that produce positive activity that will bind with the unwanted cells. Said addition is mixed into the barrel before racking or tank post-racking and then allowed to settle to the bottom of the vessel pulling out the unwanted particles that have remained in suspension in the wine. Filtering takes fining to the next level. Filtering can play an important role in the production of the final product. When you filter a wine, you guarantee that the whole body of the wine will be subject to electrokinetic activity that once again helps remove any microbacteria. Fining and filtering can help ‘polish' a wine by removing its rough edges and improving its texture and clarity.
A History of a Wine's Chemistry Analysis
Chemistry analysis is an important contributor throughout the life of the wine making process. During the cold soak, we will look at the wine's nutrient profile, sugar content and acid which will guide us through the pending fermentation and cue us in as to whether we will need to be adding any nutrients to facilitate a healthy conversion of grape juice to young wine. Once the wine finishes fermentation the standard chemical analysis of the wine will include: pH (the general indicator of acidity in a wine; water is neutral at 7 pH, while white wines will be in the low 3's and red wines in the mid to upper 3's; thus acidic); RS (“residual sugar” or the glucose and fructose that remain in a wine after these sugars have converted to ethanol concentration or alcohol; each wine and each winemaker will have their own threshold as to what is acceptable RS in a wine. We consider our wines to be ‘dry' (i.e. lacking sugar) at less than 1 g/L. Late harvest or dessert wines can be judged as such if they have more than 4g/L residual sugar); Alcohol (self explanatory) and VA (or “volatile acidity” which is predominantly acetic acid that is produced by spoilage yeast and bacteria in a wine and can cause the development of unwanted sensory effects. Wines with high acetic numbers can also cause the formation of ethyl acetate that is a common microbial flaw. At high levels, ethyl acetate produces the dreaded nail polish remover character in a wine; at lower levels it can produce a potential sweet, richness).
Throughout the life of the wine's maturation the sulfur levels are monitored and adjusted to preserve the wine. Appropriate levels of sulfur in a wine during aging will act as an antioxidant and will prevent microbial growth. The absence of sulfur in a wine and the presence of oxygen is the biggest threat to the wine's health. During the wine's life in barrel, we strive for sulfur levels in the mid-30's and we will bottle our wines at levels around 25 to 28 mg/L (or parts per million, PPM).
With the basic chemistry established and at acceptable levels throughout maturation, it is now time, pre-bottling, to determine whether or not the wine has any remaining spoilage yeasts and bacteria that produce off character(s) in wine. The most common ‘flaws' that develop during primary and secondary fermentation are as follows: Oenoccoccus, a malolactic bacteria that will produce high levels of acetic acid; Brettanomyces is an easily distributed volatile acid, ester and phenol that is responsible for the off-aromas and barnyard flavors we commonly know as Brett; Lactobacilius, another malolactic bacteria that forms during sluggish fermentations produces that buttery character in a wine; Pediococcus is yet another lactic bacteria that can cause textural defects that suppress the fruit character in a wine and prevent the healthy aging of a wine. The appropriate chemistry analysis of these bacteria will let you know if you have any of these miscreant cells remaining in your wine. Although some of these cells may be present, there is a good chance that they are ‘dead cells' that were neutralized during the healthy process of sulfur maintenance. If we feel that the wine is in jeopardy due to high levels of any of these cells, we will make the decision to filter the wine.
A short cut to checking if a wine has problems is to check its turbidity, i.e. the wine's clarity or haziness. Turbidity will help determine whether a wine has any suspended solids. Those solids may include the yeast cells or the microbacteria listed above; however, as mentioned, those solids may or may not be active in deteriorating the wines. It is up to the winemaker to make the judgment based on the full chemistry analysis as to whether or not they wish to clarify the wine further through filtration, to finish and polish the final product or to free it from the potential danger of those bacteria attacking the character of the wine.
As I type this, I am happy to report that we have the full chemistry analysis of our Merlot blend, Firebelle. The wine has a pH of 3.9, RS of less than 1g/L, VA of less than 1g/L, Alcohol at 14.5% and no spoilage bacteria whatsoever. The turbidity of the wine is 25 NTU and we'd like to see that lower than 15; so, we are going to rack the wine from tank to tank because during the process of moving the wine from barrel to tank, it is likely that you will shake up some solids which we are comfortable knowing will settle out once again in the weeks ahead pre-bottling. So, looks like a near perfect (chemical) wine. But most importantly, how does it taste? Well, that is for you to decide when the wine releases January 2010. I'll report back in a couple of weeks with a photo essay of the bottling process. Until then, thanks for reading.
Larkmead Vineyards in Napa Valley. Dan has an MBA from New York University and worked as an Ad Exec in New York for several years, before switching it up and trading his suit for a move out west