Egg White Protein Coagulation Sequence — Ovalbumin and Conalbumin

The systematic study of egg white protein fractions dates to mid-twentieth century food chemistry, but Harold McGee's 2004 revision of On Food and Cooking gave working cooks a coherent framework for understanding why egg whites firm at different temperatures depending on which proteins dominate. Heston Blumenthal and the Fat Duck kitchen operationalized this research directly into precise low-temperature cooking protocols for set custards and meringue work.

Egg white is not one protein — it is a committee, and the committee members disagree about when to set. Conalbumin, which makes up roughly 12–13% of egg white solids, begins denaturing and coagulating around 61–62°C. Ovalbumin, the dominant protein at roughly 54% of total solids, does not fully coagulate until 80–84°C. This staggered sequence is the whole game when you are cooking egg whites to a specific texture. If you pull a white at 65°C, conalbumin has set and the structure is just barely holding — yielding a trembling, barely-opaque gel. That is what you want for a soft-set white in a slow-poached egg or a delicate warm custard. Push to 80°C and ovalbumin catches up, tightening everything down into the firm, rubbery texture most people have been eating their whole lives and calling 'overcooked.' The window between conalbumin set and ovalbumin set is your working zone. Outside of temperature, pH matters. Acid — cream of tartar in a meringue, vinegar in poaching water — shifts the isoelectric point of the proteins toward a tighter network at lower temperatures, which is why acidulated poaching water produces a more compact, cohesive white. Salt does the opposite at low concentrations, slightly loosening network formation and producing a more tender curd. Sugar in a meringue delays ovalbumin coagulation significantly, which is why Italian meringue survives hot syrup without curdling the foam. McGee's data on these temperature thresholds, cited in On Food and Cooking pages 100–102, maps directly to the graduated textures you can produce by controlling a water bath or a low-heat pan to within two or three degrees. The practical takeaway: treat egg white proteins as a two-stage system, not a single on/off switch, and your poached whites, hot soufflés, and angel food structures gain real precision.

High-heat ovalbumin coagulation above 80°C triggers the Maillard-adjacent degradation of sulfur-containing amino acids — primarily cysteine and methionine — releasing hydrogen sulfide and other volatile sulfur compounds. This is the 'rubbery boiled egg' smell and flavour. Keeping whites below 80°C by working in the conalbumin-only window produces almost no sulfurous volatiles, and the flavour remains clean, milky, and lightly savory. The Maillard reaction itself is suppressed in the presence of high water activity and low reducing sugars typical of plain egg white, so browning and associated roasted notes only develop when surface moisture evaporates — as in a dry-heat meringue or baked white — not from internal coagulation temperature alone.