How Aluminum Corrosion Actually Happens in a Wine Can

Aluminum cans are protective because the metal forms a thin oxide layer (Al2O3) on contact with air or water. In wine's acidic environment (pH typically 3–4), that protective layer starts to dissolve once pH drops below about 3.9 — exposing bare aluminum underneath the liner wherever it's imperfect or damaged, and kicking off corrosion.

Once exposed, aluminum corrodes in a fairly specific, localized way called pitting corrosion: small pits form at weak points in the oxide layer, driven partly by chloride ions in the wine, which help break down the passive layer and accelerate metal dissolution at the anode. This is a two-step process — initiation (the pit starts) and propagation (corrosion products diffuse outward into the wine) — and it's the same basic mechanism seen in other packaged acidic beverages.

The wine-specific twist is sulfur dioxide. Unlike a plain acidic beverage, wine and cider are typically preserved with SO2, and once aluminum is exposed, SO2 reacts with it to generate hydrogen sulfide gas directly: aluminum metal donates electrons that reduce SO2 to H2S, while the aluminum itself dissolves into the wine as Al3+. This reaction is favored thermodynamically over the alternative pathways that produce other, less-pungent sulfur off-flavors (like methanethiol), which is why H2S specifically — not other reduced-sulfur compounds — dominates canned wine off-aromas.

A useful way to think about a can's redox environment: wine inside a sealed can has essentially no oxygen ingress, so its redox potential stays low (reducing) throughout storage, unlike a corked or screwcapped glass bottle where the redox potential slowly rises as trace oxygen gets in. That low, unchanging redox potential is exactly the condition under which H2S and other reduced sulfur compounds are thermodynamically favored and stay in their smelly, "free" form rather than shifting to odorless oxidized or metal-bound complexes. This is part of why canned wines, on average, contain more than 10x the H2S of the same wines in glass.

Practically, this points to the same levers producers already have available: molecular SO2 and pH management before canning, minimizing labile copper (which can catalyze pitting and also forms H2S-releasing complexes), and — as covered in our other liner-focused articles — choosing a liner chemistry and supplier proven to resist this specific chemistry, since the liner is the only thing standing between the wine and this reaction in the first place.

Source: Versari, Ricci, Pavez Moreno & Parpinello (2023), "Packaging of Wine in Aluminum Cans – A Review," American Journal of Enology and Viticulture 74:0740022.