The chemical reaction that makes century eggs black (2024)

FAQs

The chemical reaction that makes century eggs black? ›

Sodium hydroxide is alkaline. As it breaks down the egg's protein into glucose and amino acids, the two chemicals react. This reaction, called the Maillard reaction, produces the distinct color of century eggs. It's also what causes browning when you fry bacon on a pan or roast meat in an oven.

Sodium hydroxide, produced by the reaction of sodium carbonate, water, and calcium oxide in the brine or coating paste, penetrates the eggshell, turning the egg white into a brown, semi-translucent gelatinous texture and the egg yolk into a dark green semi-solid or solid in 20–50 days depending on the method used (Wang ...

The egg white or albumen changes colour to a brown or greenish brown, with a gel-like texture; the egg yolk changes colour to blackish green, grass green or dark brown. The colour change has been partly contributed to the Maillard reaction between the glucose of the albumen and amino acids.

Chemical Fermentation

water (H2O) react to produce sodium hydroxide (NaOH). The NaOH diffuses through the eggshell and disassembles the 3-dimensional protein structure of the egg white. The protein fragments interact with one another, and with water, and the runny egg white gets converted to a gel.

The water that they are boiled in contains sulfur and iron, thus giving the shells their unique color. The black eggs, commonly called Kuro-Tamago by the locals, are perfectly safe, although they may smell like sulfur.

Sodium hydroxide is alkaline. As it breaks down the egg's protein into glucose and amino acids, the two chemicals react. This reaction, called the Maillard reaction, produces the distinct color of century eggs. It's also what causes browning when you fry bacon on a pan or roast meat in an oven.

To begin with, in a raw egg the long protein molecules are individually coiled up. However, as we heat them, these chains begin to unfold, a process known as 'denaturing'. Once unravelled, the proteins form a three-dimensional network, trapping water into tiny pockets in the network, and causing solidification.

While they still don't entirely understand it, they do know the basics: The Maillard reaction is many small, simultaneous chemical reactions that occur when proteins and sugars in and on your food are transformed by heat, producing new flavors, aromas, and colors.

If made properly, century eggs are completely safe. There was once a rumour that century eggs were made by soaking them in horse urine, but that's not true. If you buy your century eggs from a shop, check the label to make sure they weren't made with lead oxide – eating foods with lead oxide can be harmful.

Century eggs take about 4-5 weeks to make, a few minutes to work up the courage to open, and a few seconds to eat. Traditionally century eggs were made by preserving chicken or duck eggs in a mixture of salt, lime and ash, then wrapping in rice husks for several weeks.

Can Muslims eat century eggs? ›

Brief Answer: The ruling of eating the century egg is halal based on the Islamic legal maxim which states “The original rule for food is halal unless there is a dalil which states on its prohibition”.

Century eggs are a type of egg traditionally made in China and other Asian countries, like Hong Kong and Taiwan, by preserving the egg for many weeks or months in a mixture of clay, salt, wood ash, and quicklime.

The eggs are high in calories. So it's essential to consume them in moderation. Limiting your intake of century eggs to 1 or 2 eggs per day is recommended as a general guideline. It allows you to enjoy their unique flavor and nutritional benefits without over consuming them.

Black or green spots inside the egg may be the result of bacterial or fungal contamination of the egg. If you come across an egg with black or green spots discard the egg. Off color egg whites, such as green or iridescent colors may be from spoilage due to bacteria.

Ways to make century eggs

Using option one, mix rice hulls, clay ash, lime powder, and salt in an earthen pot. Place the duck eggs in the pot and cover them completely with the mixture. Cover the pot and place it in a dry, dark area for six to eight weeks. If you do not have clay ash, use a mix of clay or wood ash.

A chemical reaction occurs with between the vinegar and calcium carbonate. This reaction will create carbon dioxide. If you look closely, you may see tiny bubbles forming on the side of the eggshell and float to the surface. The reaction will eventually dissolve the eggshell.

“When an egg is cooked for too long and/or at too high a temperature, the sulfur in the egg white combines with the iron in the yolk and creates ferrous sulfide, which has a green tint,” she explains. Unfortunately, this chemical reaction—which scientists call denaturation—isn't limited to hard-boiled eggs.

Through the process, the yolk becomes dark greenish grey in color, with a creamy consistency and strong flavor due to the hydrogen sulfide and ammonia present, while the white becomes dark brown in color, with a translucent jelly-like appearance and salty flavor.

Acetic acid CH₃COOH reacts with calcium carbonate CaCO₃ contained in an egg shell, thus dissolving the latter. This reaction yields calcium acetate. The egg itself becomes soft and rubbery to touch.