Our last context discussion was on sugar in wine, if you missed it you can find it here. This time around I wanted to discuss Sherry and clarify what type of wine this can be, as it's often misunderstood, and why it is actually that way from a process standpoint. There are two major camps of process that will dictate the finished style - biologically aged and oxidatively aged. Both of these approaches will include the fractional blending system of solera but they differ in the inclusion or exclusion of flor.
Let's start with the easy one, oxidative aging, which is fairly self explanatory in the title. The wine is introduced to barrels in the criadera of the solera and is aged there until the scales are run and it's fractionally been blended with another criadera and so on until it is bottled. This process usually takes years and during this time the wine is exposed to oxygen just like any other still wine is during barrel aging, but at a more subjected degree due to the extended time in barrel. So what you end up with are very oxidative characteristics in the wines - toffee, roasted nuts, dry caramel, dried/dessicated fruits, torrefaction etc. They are very aromatic and rich, which is where the name oloroso is derived from, meaning odorous in Spanish. These wines are defined as being chemically oxidized, meaning that the entire wine in all it's components have been exposed to oxygen and transformed due to that exposure. Phenols, anthocyanins, alcohol and other components in the wine are together altered to create what we perceive in the the glass and is the magic of the style.
Biologically aged wines on the other hand will be aged in criaderas with the inclusion of flor living in tandem with the wine. Flor is a type of yeast and is an amazing collection of little organisms that grow on top of the wine and feed off a number of things in the wine including alcohol (both ethanol and glycerol), sugars and most importantly for this initial discussion - oxygen. The film of flor on top of the wine will protect it from oxygen from above and will consume any oxygen dissolved in the wine from ingress through oak and or racking from below. This makes all biologically aged wines reductive wines. The definition of reductive is the absence of oxygen, but I often hear fino or manzanilla being described as oxidative which is not the case. Now, there are characteristics that invoke flavors reminiscent of oxidation like almonds, saline and such, therefore it is easily confused. These are a result of a process of flor that will biologically oxidize one particular component of the wine which we'll dive into on the next post. All the other components are not oxidized.
See you in the next post for the nerdy details!
Ok gang, not on to the details of what flor is doing to that ethanol and how it becomes oxidized without being exposed to oxygen. Flor has a survival mechanism that is designed to provide a future food source for if/when all the goodies run out in its current environment. This delicious dish is called pyruvate, and it can be converted from an essential part of what we love about biologically aged styles : acetaldehyde. Acetaldehyde is naturally present in ripe fruit, bread and coffee among other things and has a sour green apple type of aroma and flavor. In Sherry, it is produced by flor producing an enzyme that will snip a hydrogen from the ethanol, oxidizing it and transforming it into acetaldehyde for future use for food. It doesn't have the chance to ever utilize it as the solera is refreshed with newer wine with plenty of food for the flor, and then the wine is separated and bottled without flor, but we benefit from that sour and tasty acetaldehyde in our sherry. Amusing enough, acetaldehyde is also primarily responsible for causing the feeling of a hangover as well, so be sure to drink plenty of water with your Sherry
We call this biological oxidation.
Another quick and interesting fact is that biological styles of Sherry are some of the most lees affected wines in the world. It has flor growing on top of the wine, strands of flor from recently deceased and/or dying flor cells hanging from the live raft down into the wine, and then dead flor cells on the bottom of the barrel. Photo courtesy of bitter booze.com
Thought this article might be of interest.
Acetaldehyde as Key Compound for the Authenticity of Sherry Wines: A Study Covering 5 Decades
Thank you Chris. Lovely reading about the bio oxidation. Tons of thanks for the information
Do you think it's fair to refer to Fino/Manzanilla production as a reductive winemaking style? I read one article that referred to it as such, and I never really thought of it that way, but I suppose it's technically true.
Hoping you discuss acidity in Sherry next. I love how many wine people are quick to bash any New World wine that has had its acid adjusted, whilst admiring their large and esoteric Sherry collection.