The fall of financial markets in 2008 led to several significant changes at our winery. While the reduction of cash flow was certainly one of them, it was the creation of a new brand and market which amazed me most. We are by no means a super premium winery, but our target market used to consist of a lot of over $20 a bottle drinkers. To stay competitive in our rapidly shrinking market, we had to come up with a way to make the same quality wine at a cheaper price. At first, this may seem like an oxymoron, but with a sharp decrease in demand the prices for grapes fell significantly. This was the first hurdle to overcome, and a relatively easy one. The real challenge began after the grapes landed on the crush pad.
Wine making can be oversimplified into two facts: the juice must be made into wine, and that wine must be packaged. The wine does not care what bottle it ends up in, or what the label looks like. In creating a good drinkable wine at a lower price point, the packaging choices were obvious. What the wine does care about is the closure in which it resides under. With cheaper packaging comes the decision of cork or screwcap. Before the inception of this brand, I used to scoff at screwcaps. To the inexperienced drinker, it is often a sign of low quality, reductive wines. But with the taming of the screw comes the respect of the screwcapper (in the words of Ferris Bueller, 'if you have the means I'd highly recommend picking one up'). A screwcap is a beast of a different nature, and as we learned more about the closure it taught us much more about the nature of wine in this closure.
Now for some chemistry. Thanks to the rise of the screwcap, we have a plethora of 3 letter acronyms in the bottling room. They mostly refer to the relationship of oxygen and wine, and the efficiency of oxygen in passing by the closure. In a very well known wine movie, there is a scene describing a bottle of wine as a living thing, something that matures and changes with age. This is certainly true, but not all change is good. The 'life' that drives the wine is a complicated and reversible matrix of chemical reactions involving the 'redox,' or reduction/oxidative potential of the wine. I would love to give a gen chem lesson right here, but to keep things simple I will use the acronym that I was taught. OIL RIG - oxidation is loss, reduction is gain. This refers to electron movements between molecules within the wine. To be oxidized is to lose electrons (there is a definied number for each molecule in each oxidation state). Some molecules want electrons more than others, and this difference in affinity gives rise to cascading chemical reaction. That is to say there is a strong interconnection between A and D when A reacts to form B, B reacts to form C, and C reacts to form D. What stops that reaction from reaching equilibrium and hence ceasing to age? OTR, or oxygen transmission rates. Each modern closure lets a predictable amount of oxygen react with the wine during aging ( perhaps this gives rise to bottle shock? oxygen is introduced during bottling and then the wine is closed. it would seem to me a macro-equilibrium would need to take effect, thus explaining the change in taste after bottling).
I could write for days about the reactions of oxygen and wine, but for now I want to concentrate on the reductive qualities associated with a screwcap. The approach to winemaking must consider the closure which the wine will end up under, and the period of time the winemaker has to stabilize the redox state of the wine.
Wines begin their life with a huge desire for oxygen. Yeast have a hunger for oxygen, and if they do not get it poor fermentation and off aromas will develop. After primary fermentation, the wine still needs a substantial amount of oxygen to aid in the aging process (like every rule, there are exceptions to this. and also I am thinking WV pinots here). Anyone who has opened a tank to the smell of deep cooked meat and earth has seen this first hand. An excellent indicator of reduction in the early stages of winemaking is the formation of hydrogen sulfide, H2S. H2S is in a redox equilibrium with SO2 (or O2S of you would prefer). Organic chemistry simplifies redox relationships to say a molecules' oxidation state changes when the number of oxygen bonds change. This is a firsthand example. In a reduced environment, sulfur easily exchanges its oxygen molecules for two hydrogen molecules. Upon introducing excess oxygen, H2S is oxidized from its farty smell back to the wonderfully choking SO2 stench. Cellar operations during harvest use this principle, the winemaker should splash rack in order to provide the necessary oxygen and age the wine. The oxygen consumption potential of a young red wine is huge, oxygen is in high demand and is broken down from atmospheric dioxygen into individual molecules which fit like puzzle pieces in the chemical matrix. As the wine is allowed to use oxygen where it is needed, the consumption potential begins to fall. This is where the winemaker must make educated decisions about the timing of bottling under screwcap (a post for another day...the best time to treat H2S and mercaptans is in a very reductive state, more to come...).
A major concern when bottling under screwcap is the presence of disulfides and mercaptans (thiols). The two are closely related. A mercaptan is the sulfur containing analog of an alcohol. For example, methanol has the formula CH3OH. Methanethiol has the formula CH3SH. Sulfides have a unique property of forming a disulfide bridge. The two sulfur atoms can form a covalent bond and stick together in the formula CH3SSH3C. This will occur in a reductive environment and is of significant concern. The human nose has a 20 part per billion sensitivity for DMDS, versus a sensitivity in the parts per million range for a thiol. I say it is a significant concern because under screwcap, reduction is imminent. Even though the wine smelled clean before bottling, disulfides can rear their ugly head after a year or two under screwcap, making the wine offensive and unpalatable. The younger the wine, the more aggressive the reduction will be. A young red wine bottled under screwcap should raise a large red flag in the winemaker's brain, because it risks harming the potential of the vintage. The goal of bottling is to have the wine come out as good or better than when you put it in there. Modern wine making with screwcaps requires a modern approach.
The first approach I typically see is sulfide remediation. this involves sealing the wine after introducing a strong reducer, ascorbic acid, and letting the disulfide bridges revert back to thiols. This is a slow process, but it will work. After a predetermined amount of time, the winemaker must then treat (after a lab trial!) with copper sulfate. The copper serves as a much stronger bridge between thiols. When it enters the wine, it leaves the sulfate to complex 2 thiols. The resulting complex drops out and is lost either during racking or filtration. If it is not, no worries; the bond will not break. The copper oxidizes the thiols and is referred to as an oxidizing agent. For this reason, we use copper as a preventative treatment under all screwcap. As reduction begins to set in, the copper should 'mop' up any thiols which begin to form. Since the offending chemicals are often in ppb concentrations, and the legal limit of residual copper is 0.5ppm, copper should always be the excess reagent and capable of reacting. This can be a particularly useful technique if the wine is to be bottled a few months after fermentation.
A second technique I have seen is a macro-oxygenation of the wine at bottling. I call it macro because the oxygen is not slowly metered in, we literally ram it in with and air pump and a sparging stone. Once it reaches our desired concentration, estimated by cellar trials, we bottle. The idea is to still have some dissolved oxygen present in the bottle to delay the onset of reduction. I have only seen this done on wines designed to be depleted within 1 year of the bottling date. And I am not completely sold, because it almost always comes with a complimenting increase in the SO2 before bottling to offset the SO2 loss associated with oxygen pickup (and Ascorbic if you used that).
A third solution is slowly developing, and that is screwcaps with designed differences in OTR. If the winemaker knows most of the wine will be drank within 1 year, it is an option for them to select a screwcap with a much greater OTR than cork. This runs a huge risk of turning the bottle to vinegar, but generally those things are worked out with sales and marketing ahead of time.
So the next time you drink wine out of a screwcap and it tastes good, I hope you have more of an appreciation for the work that went into making that wine. I can promise you that the winemaker does.