Egg white is a base, not an acid. At the moment a hen lays an egg, the white (albumen) already sits at a pH around 7.6 to 8.5, which is slightly alkaline. Within days, that number climbs above 9.0 and keeps rising, pushing egg white firmly into basic territory. The reason for the shift involves a gas you breathe out every few seconds, and understanding it explains a surprising number of kitchen puzzles, from why old eggs peel more easily to why angel food cake recipes call for cream of tartar.
What Happens Right After an Egg Is Laid
Inside the hen’s oviduct, the freshly formed egg is saturated with dissolved carbon dioxide. That COâ‚‚ acts like a weak acid in solution, holding the albumen’s pH relatively close to neutral. Measurements taken at the moment of laying typically put it in the range of 7.6 to 8.5.1Poultry Science. Influence of carbon dioxide on the activity of chicken egg white lysozyme Even at this early stage the white is already on the alkaline side of the pH scale, where 7.0 is neutral. So there is no point in the egg’s life when the white is acidic under normal conditions.
Once the egg leaves the hen, things change fast. The eggshell looks solid but is riddled with thousands of tiny pores that allow gas exchange. Carbon dioxide escapes through those pores into the surrounding air, and as it does, the buffering acid it provided disappears with it. The result is a steady climb in pH. Research tracking this process found that the albumen pH rises from about 7.6 at oviposition to values exceeding 9.0 within four to five days, regardless of whether the egg is stored at refrigerator or room temperature.2Food Hydrocolloids. Storage induced conversion of ovalbumin into S-ovalbumin in eggs impacts the properties of pound cake and its batter Room temperature just gets the egg there a bit faster.
How Alkaline Egg White Gets During Storage
The pH does not rise forever, but it reaches a surprisingly high plateau. Fresh egg whites in one study started around pH 9.0 and climbed to about 9.4 during storage.3Journal of Food Protection. Effect of Temperature and Time of Storage on Protein Stability and Anti-Salmonella Activity of Egg White Another study tracked uncoated eggs and recorded albumen pH rising from 8.23 all the way to 9.51 over the storage period.4PubMed. Oil coating affects internal quality and sensory acceptance of selected attributes of raw eggs during storage To put a pH of 9.5 in perspective, that is in the same ballpark as a dilute baking soda solution. It is noticeably alkaline.
The speed of the shift depends on temperature and the condition of the shell. Warmer storage accelerates CO₂ loss, which is part of why eggs stored at room temperature in a market lose freshness faster than refrigerated ones. Eggs stored at around 23 °C reached a pH of 9.5, while those at 6 °C reached 9.3 over the same period.2Food Hydrocolloids. Storage induced conversion of ovalbumin into S-ovalbumin in eggs impacts the properties of pound cake and its batter The difference sounds small, but in cooking and food science even a fraction of a pH unit changes how proteins behave.
Why Would a Natural Defense System Be Alkaline
The egg white is not just a cushion for the yolk. It is the egg’s immune system, packed with proteins whose job is to stop bacteria from thriving. Lysozyme, the most famous of these, physically breaks apart certain bacterial cell walls. Ovotransferrin binds iron so tightly that bacteria starve for it. Together, the proteins create a hostile environment for microbes, and the high pH is part of the hostility.
Most foodborne bacteria prefer a near-neutral environment, roughly pH 6 to 7.5. By pushing its pH above 9, egg white makes life difficult for organisms that might invade through a cracked shell. Lysozyme’s activity is itself influenced by the amount of dissolved COâ‚‚ in the white, tying the gas-escape process directly to antimicrobial function.1Poultry Science. Influence of carbon dioxide on the activity of chicken egg white lysozyme The rising pH also changes how other defense proteins fold and interact, reinforcing the protective barrier around the developing embryo or, in the case of unfertilized grocery-store eggs, around the yolk.
What Rising pH Does to Egg White Proteins
As the albumen becomes more alkaline during storage, the proteins in it do not simply sit there unchanged. One of the most studied transformations involves ovalbumin, the single most abundant protein in egg white. Over time at high pH, ovalbumin converts into a form called S-ovalbumin, which is more heat-stable and resists denaturation. Higher pH and higher storage temperatures both accelerate this conversion.2Food Hydrocolloids. Storage induced conversion of ovalbumin into S-ovalbumin in eggs impacts the properties of pound cake and its batter The practical consequence is that older eggs behave differently in baking. Pound cake batter made with aged, high-pH egg whites produces a different texture than batter made with fresh whites, partly because S-ovalbumin does not unfold and set the same way during baking.
Lysozyme, the antimicrobial protein, also has an interesting relationship with pH, though from a stability standpoint it actually prefers a mildly acidic environment. Research on lysozyme’s thermal behavior showed it is most thermally stable around pH 5.0, with stability declining as pH rises toward 7.0 and above.5PubMed Central. Thermal stability of high concentration lysozyme across varying pH: A Fourier Transform Infrared study This might seem contradictory given that the egg white is naturally alkaline, but it makes sense when you consider that lysozyme evolved to work at the pH of the egg white, not to survive a frying pan. Its antibacterial action at high pH is separate from its heat tolerance.
Why This Matters in the Kitchen
The alkalinity of egg white quietly shapes some of the most common cooking outcomes people complain about or celebrate.
Hard-boiled eggs are the classic example. Anyone who has tried to peel a hard-boiled egg made from very fresh eggs knows the frustration: the white clings to the shell membrane in ragged chunks. The reason is pH. At lower pH, the proteins in the white bond more tightly to the inner shell membrane. As pH rises during storage, that bond weakens. Research specifically confirmed that the pH of raw albumen is a reliable predictor of how easily the cooked egg will peel, with a pH above about 8.9 producing easy-to-peel results.6Poultry Science. Effect of Storage Conditions on Albumen pH and Subsequent Hard-Cooked Egg Peelability and Albumen Shear Strength This is why many cooks recommend using eggs that are at least a week old for boiling, and why some add baking soda to the cooking water: it nudges the pH even higher.
In baking, the opposite concern sometimes comes into play. Angel food cake depends on whipped egg whites for its structure, and the natural alkalinity of the whites can work against you. A very alkaline white produces a coarser, less stable foam. That is where cream of tartar, an acid salt, earns its place in the recipe. Adding it lowers the pH of the egg whites, tightens the protein network in the foam, and produces a finer, more stable structure. Studies on angel food cake found that increased cream of tartar decreased pH and improved both the tenderness and the appearance of the finished cake, including a whiter interior crumb.7Family and Consumer Sciences Research Journal. Effect of Cream of Tartar Level and Egg White Temperature on Angel Food Cake Quality Lemon juice and vinegar serve a similar function: they are kitchen acids counteracting the natural basicity of the egg white.
Slowing Down the pH Rise
Since the pH climb is driven by COâ‚‚ escaping through the shell pores, anything that blocks those pores slows the change. Coating eggs in oil is one of the oldest and simplest preservation tricks, and it works remarkably well for this specific purpose. In a study comparing coated and uncoated eggs, the albumen pH of uncoated eggs climbed from 8.23 to 9.51 during storage, while oil-coated eggs barely budged, staying around 8.32.4PubMed. Oil coating affects internal quality and sensory acceptance of selected attributes of raw eggs during storage Glycerol-coated eggs fared almost as badly as uncoated ones, suggesting the coating needs to form a truly gas-tight seal to work.
An even more targeted approach involves exposing eggs to carbon dioxide gas before sealing the shell with oil. Early research in Canada showed that if you first lower the albumen pH by saturating the egg with COâ‚‚ and then oil the shell to trap the gas inside, the egg retains its quality far longer than oiling alone.8Canadian Journal of Research. PRESERVATION OF EGGS: VII. EFFECT OF AGE OF EGG AND CARBON DIOXIDE CONTENT AT TIME OF OILING ON KEEPING QUALITY This COâ‚‚-then-oil method effectively reverses the pH rise by putting the gas back in, then locks the door. It improved yolk index, albumen height, and the proportion of thick white, all markers of freshness. Some modern egg producers use variations of this idea in commercial packing, though refrigeration has largely taken over as the primary shelf-life tool in many countries.
Century Eggs and Extreme Alkalinity
If normal storage takes egg white from mildly alkaline to moderately alkaline, century eggs (also called pidan or preserved eggs) blow past that range entirely. These traditional Chinese preserved eggs are cured for weeks in a mixture containing strong alkali, typically sodium hydroxide or potassium hydroxide packed in clay and rice hulls. The alkali penetrates the shell and drives the pH of the white far above anything that happens naturally.
Research tracking what happens to egg white proteins during this pickling process found that as pickling time increased, the pH of the preserved egg white kept climbing and the texture hardened.9PubMed. Relationship between protein structure changes and in vitro digestion of preserved egg white during pickling The proteins denature extensively, which is what transforms the white from a clear, viscous liquid into a dark, semi-translucent gel with an entirely different flavor profile. Interestingly, the protein digestibility of the preserved white peaked at day 14 and then dropped as pickling continued to day 42, suggesting there is a sweet spot where alkaline denaturation opens up the proteins for digestion, but beyond that point further structural changes, including an increase in tightly packed protein sheets, make the proteins harder to break down.
Laboratory studies on fresh egg white have also demonstrated a curious response to strong alkali exposure. When treated with increasing concentrations of sodium hydroxide, egg white goes through a sol-gel-sol transition: it starts as a liquid, sets into a firm gel, and then, at higher alkali concentrations, liquefies again.10PubMed. The sol-gel-sol transformation behavior of egg white proteins induced by alkali The gel that forms is stiffer and lighter in color, with altered surface chemistry, but it collapses back into a liquid as the alkali concentration climbs further. Century egg producers historically learned to navigate this chemistry by trial and error, landing on alkali concentrations and timing that produce a stable gel rather than overshooting into a runny mess.
Does the Alkalinity of Egg White Affect How You Digest It
The pH of egg white proteins at the time you eat them does influence what happens in your stomach, though not in the straightforward way you might expect. Your stomach acid is powerful enough (roughly pH 1.5 to 3.5) to overwhelm whatever pH the egg white started at, so the alkalinity of the white itself is not going to neutralize your stomach or change your body’s overall acid-base balance in any meaningful way.
What the pH does affect is the protein’s structure before it hits your digestive system, and structure determines how easily digestive enzymes can do their work. Research comparing egg white proteins pre-treated at different pH levels found that alkaline treatment (pushing the pH to 12 and then back down to 7) actually led to greater digestion in the stomach phase and generated more potentially bioactive peptides than acid-treated samples did.11Food Research International. Effect of pH treatment on egg white protein digestion and the peptidomics of their in vitro digests The likely explanation is that extreme alkaline conditions partially unfold the tightly coiled proteins, giving pepsin (the main stomach enzyme) more exposed surface to grab onto. All pH treatments in the study reduced overall protein digestibility compared to untreated whites during the gastric phase, but among the treated groups, the alkaline ones performed better than the acidic ones.
For the average person eating a regular cooked egg, this is academic. Cooking denatures the proteins far more dramatically than the natural pH shift does, and your stomach handles cooked egg white efficiently. But for food scientists working on protein supplements, infant formulas, or other processed egg-white products, the interaction between pH history and digestibility is a real design consideration.
Egg Yolk Is a Different Story
It is worth noting that the yolk does not follow the same pH trajectory as the white. Freshly laid yolks sit at a pH around 6.0, which is slightly acidic. Over storage the yolk pH rises too, but more slowly and to a lesser degree than the white’s, generally reaching about 6.4 to 6.9 depending on conditions. The yolk and white are separated by the vitelline membrane, which limits chemical exchange between the two compartments. So while the white is racing toward pH 9.5, the yolk stays much closer to neutral.
This pH difference between the two compartments has practical importance. The yolk’s near-neutral pH means it is a more hospitable environment for bacteria than the highly alkaline white. If the vitelline membrane weakens or breaks during storage (which also happens faster at higher temperatures and higher pH), bacteria that have survived in the white can migrate into the nutrient-rich yolk and start multiplying. This is one reason food safety guidelines emphasize keeping eggs cold: refrigeration slows both the pH rise and the membrane deterioration that eventually lets bacteria access the yolk.
The difference also matters to cooks. Yolk-based sauces and custards behave differently from white-based foams and meringues in part because the starting pH environments are different. Yolks do not need cream of tartar to bring down an excessively alkaline pH. Their chemistry sits in a fundamentally different range, which is one more reason recipes that call for separated eggs treat the two components so differently.