Sherry
Flor yeast on the surface of the wine. Biological ageing that prevents oxidation. Or deliberate oxidation at 17–18% ABV. And a solera that may be 200 years old.
Codex Definition
Sherry (Jerez-Xérès-Sherry) is a fortified wine produced in the Marco de Jerez, a defined DO zone in the provinces of Cádiz and Sevilla, Andalusia, southern Spain — centred on the cities of Jerez de la Frontera, Sanlúcar de Barrameda, and El Puerto de Santa María (the 'Sherry Triangle'). Sherry is regulated by the Consejo Regulador del Vino Jerez-Xérès-Sherry y Manzanilla-Sanlúcar de Barrameda. The base wine is produced from three permitted grape varieties: Palomino Fino (~90% of production — neutral, low-acid grape ideal for fortification and biological ageing), Pedro Ximénez (PX — very sweet, sun-dried raisined grapes for sweet sherries), and Moscatel (small quantities, very sweet). The base wine is fortified with grape spirit to 15–15.5% ABV for biologically aged styles (Fino, Manzanilla, Amontillado in its early stage) or 17–18% ABV for oxidatively aged styles (Oloroso, Palo Cortado). The critical biological ageing mechanism is flor — a layer of film-forming yeast (Saccharomyces beticus and related species) that forms on the surface of the wine in barrels partially filled with headspace, protecting the wine from oxidation while consuming residual sugars and glycerol.
Flor — the yeast that defines Fino and Manzanilla
Flor (Spanish for "flower") is a film of yeast — primarily Saccharomyces cerevisiae var. beticus and related strains including S. montuliensis, S. rouxii, and S. cheresiensis — that grows on the surface of Fino and Manzanilla sherry in the partially filled American oak butts (butts are filled to approximately 5/6 capacity — the remaining headspace allows flor to develop). Flor acts as a biological barrier between the wine and the air — consuming oxygen and protecting the wine from oxidative browning while simultaneously metabolising ethanol (consuming approximately 0.1–0.3% ABV per year), glycerol, and acetic acid, and producing acetaldehyde (the primary compound responsible for Fino's characteristic green apple / oxidative / manzanilla biscuit aroma) and other metabolites.
The reason flor grows at 15–15.5% ABV but not at 17–18% ABV: the film-forming yeast strains that produce flor are ethanol-sensitive — they can survive and grow at 15%, but are killed or suppressed above approximately 16–16.5%. Fortifying to 17–18% for Oloroso deliberately kills or prevents flor from forming — leaving the wine to age oxidatively instead of biologically.
Manzanilla (from Sanlúcar de Barrameda, on the Atlantic coast) develops a particularly thick and active flor year-round due to the cooler, moister Atlantic microclimate — producing a lighter, more delicate, saltier Fino style with more pronounced flor character than Jerez-based Fino.
The solera system — how Sherry is aged
Sherry is aged in a solera — a tiered system of American oak butts arranged in rows (criaderas) stacked or arranged by age. When Sherry is drawn for bottling from the oldest row (the solera), it is replenished by wine from the next-oldest row (primera criadera), which is itself replenished from the segunda criadera, and so on — with new wine added to the youngest row (the añada). This continuous blending means that no bottled Sherry wine has a vintage year — it is always a blend of multiple vintages — but it also means that each bottle contains traces of very old wine (the solera may be decades or centuries old in the most historic bodegas).
Sherry styles — the complete classification
| Style | Ageing | ABV | Character |
|---|---|---|---|
| Fino | Biological (under flor), min 2yr | 15–17% | Pale, delicate, dry, green apple (acetaldehyde), almond, saline, very low oxidation. Drink young and cold. |
| Manzanilla | Biological (under flor), Sanlúcar de Barrameda DO only | 15–17% | Lighter and more delicate than Fino. Distinctive saline, maritime quality from Atlantic influence. Can be "En Rama" (minimally filtered). |
| Amontillado | Biological then oxidative | 16–22% | Begins as Fino (biological), then flor dies → oxidative ageing begins. Amber. Hazelnut, dried fruits, rich, complex. Can be dry or slightly sweet. |
| Oloroso | Oxidative (no flor), min 2yr | 17–22% | Fortified to kill flor. Dark amber to mahogany. Walnut, dried fruit, tobacco, leather. Bone dry unless blended with PX. |
| Palo Cortado | Biological then oxidative (rare, difficult to achieve) | 17–22% | Begins as Fino, flor collapses unexpectedly → oxidative ageing. Combines Amontillado nose with Oloroso palate. Rare and expensive. |
| Pedro Ximénez (PX) | Oxidative, extended, from sun-dried grapes | 15–22% | Black-brown, extremely sweet, viscous. Raisin, molasses, chocolate, coffee. One of the world's sweetest wines. Used to sweeten Cream Sherries. |
| Cream / Pale Cream | Blended (Oloroso + PX sweetening for Cream; Fino + grape must for Pale Cream) | 15.5–22% | Commercial sweet styles. Cream = dark, sweet, dessert wine (Harvey's Bristol Cream). Pale Cream = sweet but pale. |
Acetaldehyde chemistry — why Fino smells like green apple and almonds
The defining aromatic compound of Fino and Manzanilla Sherry is acetaldehyde (ethanal, CH₃CHO) — produced by flor yeast oxidising ethanol via alcohol dehydrogenase (ADH). Acetaldehyde has a detection threshold of approximately 50–100 μg/L in wine, and an aroma described as green apple, almond, paint thinner, and dried bread at higher concentrations. In Fino, acetaldehyde concentrations typically range from 300–500 mg/L — dramatically higher than in unfortified wine (where acetaldehyde at such concentrations would be a serious fault). The combination of acetaldehyde with SO₂ naturally present in the wine produces 1-acetaldehyde-SO₂ adducts that are less aromatically active — a process that contributes to the modulation of acetaldehyde character in bottled Fino over time.
The flor yeast also metabolises glycerol (a fermentation by-product that adds sweetness and body to regular wine) — removing it from the Sherry and contributing to Fino's characteristic bone-dry, lean palate despite the wine's sugar-rich origin. Source: Berlanga et al. (2004) American Journal of Enology and Viticulture; Moreno-García et al. (2018) FEMS Microbiology Reviews.