The process of processing fresh eggs into preserved eggs is essentially a complex chemical reaction process. Although there are many recipes and different techniques for processing preserved eggs, the main raw materials generally include: quicklime (CaO), soda ash (Na2CO3), plant ash (the main component is K2CO3), salt, tea, etc. Based on the actual situation of students, I will only use two preserved eggs as an example to describe how to process them in the laboratory and the chemical principles involved:
l. Ash recipe
On the dining table Preserved eggs taste very delicious, but they are covered with an ugly "coat". Don't underestimate it, it is the key to making preserved eggs, which is the ash material. The formula of the ash material is: 50g quicklime, 3g soda ash, 1g plant ash, 2g salt, 20g water, and a trace amount of tea.
2． Ash preparation
According to the requirements of the ash formula, put the required ash into a container (a large beaker is enough) and prepare it with water. Quicklime first reacts with water to produce hydrated lime, and then the hydrated lime reacts with soda ash and potassium carbonate, the main component of charcoal, to produce sodium hydroxide and potassium hydroxide. The chemical equation of the reaction is expressed as follows:
CaO H2O=Ca(OH)2
Ca(OH)2 Na2CO3=CaCO3↓ 2NaOH
Ca(OH) 2 K2CO3= CaCO3↓ 2KOH
In order to fully react with the materials in the hair material, it can only be used after 24 hours after preparation.
3. Preserved egg processing
Roll the fresh eggs in the prepared ash material a few times to evenly coat the surface of the eggshell with a layer of ash powder. Take it out and roll it in rice bran or sawdust a few times. A layer of rice bran or sawdust is stuck on the ash material. Squeeze gently with your hands to tighten and place into the prepared container. The second fresh egg is treated in the same way, sealed in a sealed container, placed at an ambient temperature of 18 to 24°C, and can be eaten after 10 days.
During these 10 days of change, the inside of the egg is not as calm as a deep pool of water. The strong alkali (NaOH, KOH) in the ash penetrates into the egg white and egg yolk through the egg shell, and interacts with the protein in it, causing the protein to decompose, solidify and release a small amount of hydrogen sulfide (H2S) gas. At the same time, the infiltrated alkali will further neutralize the amino acids decomposed from the protein. The resulting salt crystals are deposited in the preserved egg whites of the gel peptide, and white "pine flowers" appear (this is also the name of preserved eggs). reasons). The hydrogen sulfide gas reacts with the minerals in the egg white and yolk to generate various sulfides, so the color of the egg white and egg yolk changes. The egg white takes on a special dark brown color and the egg yolk takes on a dark green color. Table salt can make preserved eggs shrink and separate from the shell, increasing the taste. The tannins and aromatic oils in tea can color the coagulated protein and increase the flavor of preserved eggs.