The process of processing fresh eggs into preserved eggs is essentially a complex chemical reaction process. Although there are many formulas and processes for processing preserved eggs, the main raw materials generally include: calcium oxide (CaO), soda ash (Na2CO3), plant ash (mainly K2CO3), salt, tea and so on. Based on the actual situation of students, this paper takes two preserved eggs as an example to explain how to process them in the laboratory and the chemical principle:
l.
Ash formula
The preserved egg on the dining table tastes delicious, but it is covered with an ugly "coat". Don't underestimate it, it is the key to making preserved eggs, and this is the ash. The formula of the ash is: 50g of quicklime, 3g of soda ash, plant ash 1g, 2g of salt, 20g of water and trace of tea.
2. Grey material modulation
According to the requirements of the ash formula, put the required ash into a container (just a big beaker) and mix it with water. Quicklime first reacts with water to produce hydrated lime, and then the hydrated lime reacts with potassium carbonate, the main component of soda ash and grass charcoal, to produce sodium hydroxide and potassium hydroxide respectively. 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 make the substances in the hair fully react, it can only be used after 24 hours of preparation.
3. Preserved egg processing
Roll the fresh eggs in the prepared ash several times, so that the surface of the eggshell is evenly coated with a layer of ash powder, take them out, and then roll them into rice chaff or sawdust several times, so that a layer of rice chaff or sawdust is stuck on the ash. Squeeze it gently by hand to make it tight, and put it into a container prepared in advance. The second fresh egg is also treated in this way. The container is sealed and placed at the ambient temperature of18 ~ 24℃. It can be eaten after 10 days.
During the change of 10 day, the inside of the egg is not as calm as a deep pool. The strong alkali (NaOH, KOH) in the ash material permeates into the egg white and egg yolk through the eggshell, and reacts with the protein in the egg white and egg yolk, so that protein decomposes, solidifies and releases a small amount of hydrogen sulfide (H2S) gas. At the same time, the infiltrated alkali will further neutralize the amino acids decomposed by protein, and the crystals of the generated salt will be deposited in the preserved egg white of the gel peptide, and white "Songhua" will appear (which is also the reason why the preserved egg is named). However, hydrogen sulfide gas reacts with minerals in egg white and egg yolk to generate various sulfides, so the colors of egg white and egg yolk have changed, with egg white showing a special dark brown color and egg yolk showing a dark green color. Salt can shrink preserved eggs from their shells and increase their taste. Tannin and aromatic oil in tea can color the solidified protein and increase the flavor of preserved eggs.
And why can't preserved eggs go bad for half a month or even months? First, because there is salt in it, salt has an antiseptic effect; First, alkaline substances killed the bacteria in fresh eggs that might cause corruption in protein.
10 days later. When you sit at the table and taste this delicious preserved egg, your heart will be filled with joy and you will be thinking about when to cook more. But the next time you prepare for mass production, don't forget to change the formula of ash proportionally.