May 18-20 is the Pint of science Festival, a nonprofit movement to share and discuss science in a local and casual setting. The goal is to have 2-3 scientists at a couple of bars in each city giving 20min TED style talks to lay audiences, helping spread the word on the work that they are doing. So far, 9 cities are hosting, and hopefully in years to come, this event will grow! Check out their podcasts from previous events and be sure to attend if your city is hosting!
Most foods are best as fresh as possible. I remember picking peaches at my grandfather’s ranch in Northern California and eating them on the spot. What a taste! But the exceptions to this rule are the many wines that actually need some aging to taste their best. Winemakers know this, and work to control the aging process including decisions they make about how to bottle up their product.
One aspect of aging has to do with the reaction of fruit acids with the alcohol. This process reduces sourness in the wine, but it’s really only important for very tart wines, the ones coming from cold climates.
The complex oxidation process is the second aspect of aging. When oxygen interacts with a wine, it produces many changes – ultimately yielding an oxidized wine that has a nutty aroma. This is a desired taste for sherry styles, but quickly compromises the aromas in fresh white wines.
However the oxidation process provides benefits along the way to that unwanted endpoint. Many wines develop undesirable aromas under anaerobic – no oxygen – conditions; a small amount of oxygen will eliminate those trace thiol compounds responsible for the aroma of rotten eggs or burnt rubbber. Oxidation products also react with the red anthocyanin molecules from the grapes to create stable pigments in red wine.
The way a bottle is sealed will directly affect how much oxygen passes into the wine each year. That will directly affect the aging trajectory and determine when that wine will be at its “best.”
Glass is a hermetic material, meaning zero oxygen can pass through it. But all wine bottle closures admit at least a smidgen of oxygen. The actual amount is the key to a closure’s performance. A typical cork will let in about one milligram of oxygen per year. This sounds like a tiny bit, but after two or three years, the cumulative amount can be enough to break down the sulfites that winemakers add to protect the wine from oxidation.
There are three major closure options available: natural cork and technical cork, its low budget brother made of cork particles, the screw cap and synthetic corks. Natural cork closures appeared about 250 years ago, displacing the oiled rags and wooden plugs that had previously been used to seal bottles. It created the possibility of aging wine. Until 20 years ago natural corks were pretty much the only option for quality wine. It’s produced from the bark of the tree, and harvested every seven years throughout the life of a cork oak tree, Quercus suber. The cork cylinder is cut from the outside to the inside of the bark.
A small fraction of corks, 1-2% today, end up tainting the wine with a moldy smelling substance, trichloroanisole. This TCA is created via a series of chemical reactions in the bottle: chlorine from the environment reacts with the natural lignin molecules in the woody cork to make trichlorophenol, which is in turn methylated by mold. TCA has one of the most potent aromas in the world – some people can smell as little as 2 parts per trillion in wine. So, in every eight cases of wine, one or two bottles will smell like wet cardboard or simply not taste their best. This is why restaurants let you taste the wine before pouring – to let you judge if the wine is tainted. A 1% failure rate seems high in today’s world.
Synthetic corks are made from polyethylene, the same stuff as milk bottles and plastic pipes. After years of research and development, these corks now perform nearly the same as the natural version with three exceptions: they have no taint, they let in a bit more oxygen and they are very consistent in oxygen transmission.
Their consistency is a major selling point to winemakers because the wine will have a predictable taste at various points in time. In fact, winemakers can tweak the oxidation rate of their wine by choosing from a range of synthetic corks with different rates of known oxygen transmission.
Screwcaps are actually two parts: the metal cap and the liner inside the top of the cap that seals to the lip of the bottle. The liner is the critical part that controls the amount of oxygen getting into the wine. Back when screwcaps were only used on jug wine, there were just two types of liners available. But today multiple companies are jumping in to offer their take on what rate of oxygen transmission is best, as well as to replace the tin used in one of the traditional liners. The standard liners admit either a bit more or a bit less oxygen than good natural corks. Screwcaps, being manufactured, are also very consistent.
Performance of the manufactured closures, made with 21st century technology, is excellent. Generally they approximate our expectations, based on over two centuries of experience aging with natural cork closures.
For the regular wine you might purchase for dinner this weekend or to keep for a year or two, any of these closures are perfectly good, while the manufactured closures avoid taint. In fact, your choice is more a matter of preference for opening the bottle. Do you want the convenience of twisting off the cap, or do you want the ceremony of removing the cork?
For long aging however, the only closure with an adequately long track record is natural cork. So to be safe, that is the closure to choose. Once we have solid long-term evaluations of synthetics and screw caps, it will be possible to judge their suitability for extended aging, such as more than ten years.
Over centuries, winemakers have consistently taken advantage of new technology to improve their product, from oak barrels to bottles to modern crushing and pressing equipment and micro-oxygenation. While manufactured closures have some key advantages, it is proving difficult to displace natural cork due to its centuries-old tradition, albeit with a few problems, and its connection to the natural environment.
This article is part of The Conversation’s holiday series on wine. Click here to read more articles in the series.
A report out in Human Reproduction by Pacey and colleagues analyzed the impact of lifestyle factors of 2,249 men on their sperm quality (specifically sperm morphology). While most lifestyle choices had little impact on sperm quality (examples: BMI, underwear preference, alcohol, cigarettes), smoking cannabis did significantly impact sperm quality. Two other factors also affected sperm quality, the season and abstinence. The results of this study contradict previous studies and historically held beliefs, including underwear choice, alcohol, and tobacco use. This study has the advantage of being large, and uniformity in analyzing sperm quality. However, it also only looked at sperm morphology as a measure of sperm quality. It is entirely possible that some of the lifestyle choices could negatively impact other aspects of sperm quality or semen quality.
Only three factors were independently related to case status after adjustment for clustering within centre: men who produced their sample in summer (June to August) and younger men who used cannabis in the 3 months prior to sample collection were more likely to have sperm morphology <4% normal.
This suggests that an individual’s lifestyle has very little impact on sperm morphology and that delaying assisted conception to make changes to lifestyle is unlikely to enhance conception.