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Changes in the bread baking process inside
Source： Time：2016-03-17 11:09:06 views：
Forming 1) bread billet temperature, moisture changes and internal structure
After the bread oven in the blank, while receiving heat sources or methods are: thermal radiation heating pipe, baking heat conduction, convection hot air furnace.
A. Early baking
a. Skin formation
Furnace started going green, the surface temperature is about 30 ℃, the first encounter hot air. Hot water in the air will be cold and blank condensed into water droplets adhered to the surface. But this happened in a very short period of time, and soon drops will vaporize and bread surface temperature quickly rose to above 100 ℃, so the surface will be dry and form a thin white skin.
b. Crust (shell) is formed
At the same time, the heat conduction to the inside, the inner temperature is rising, the temperature in a short time under the skin close to 100 ℃, formed outside the high low temperature gradient distribution. Such heat transfer direction (driving force) is outside-in.
The distribution of bread in the water is just the opposite, outer low in the high moisture gradient distribution. Such water is added from the inside out, and evaporated layer (due to a temperature close to 100 ℃) is formed in the lower epidermis.
However, due to the baking in progress, the internal temperature will continue to rise, when the temperature reaches gelatinized starch (higher than 50 ℃), water will be combined with starch, so that the internal complementary outwardly less and less water evaporated layer of water will reduce the temperature exceeds 100 ℃, and then dried to form a layer of dry bread crust bread shell (hygroscopic product softened after called crust).
A. Bake late
a. Bread capsule formation
Continue baking heat inwardly constantly transfer. Because of the barrier effect of the crust, and the interior gelatinized starch, diffusion out of the water is limited, but the temperature will continue to rise, eventually approaching 100 ℃, this protein will be denatured. And protein denaturation, bread shell portion is formed below the bread bag, which is also part of the aging actually.
b. Bread bag forming heart
Heat the geometric center portion of bread during the baking process have been the least, the slowest rate of temperature rise. Since the crust and the core temperature of the temperature difference is too large, the location in the middle parts of the bread bag both outward diffusion of water, condensate can penetrate inward portion. When face to face cyst formation, bread center water 2% higher than before, the final temperature generally rises to 90-98 ℃. And forming a bread bag heart.
2) inside the bread baking process microbiological and biochemical reactions occurring changes
A. Microbiology change
a. Activity of yeast
After the green into the furnace, the internal temperature of each part will rise, but the temperature rise is different. Regardless of the temperature of various parts of the bread are more than 50 ℃. Below 50 ℃, Angel Yeast has a strong gas production process, and then, as the temperature rises, reducing the yeast activity, until death. This process took about 5 minutes. But bread volume and shape are still affected.
b. Acidic microbial activity
Mainly lactic acid bacteria. Usually each part when the temperature exceeds 60 ℃, all died. If the temperature has not yet been to a balloon heart seeks baked, sometimes live bacteria can be detected.
B. Biochemical reactions
a. Amylase: α- amylase at 97 ℃, β- amylase at 82 ℃ passivation. They had been in the decomposition of starch.
b. Protease: at 80--85 ℃ passivation, after how many will break down proteins.
c. Gelatinized starch
Gelatinized starch down into maltose and dextrin. Dextrin combined with plenty of water, forming a starch gel is one of the soft palate and bread constitute an important factor.
d gluten protein denaturation: 60-70 ℃ denaturation solidification, releasing part of bound water to form a honeycomb or bread spongy tissue. This steel has a role in determining the shape of the bread is the main reason. as the picture shows.
e coupling reaction
Maillard Reaction: So 150 ℃ when large proteins, amino acids and sugars, amino carbonyl reaction of aldehydes occurred bread component. Formed from gray to golden color.
The reaction caramel: sugar above 180 after the formation of caramel color.
Enzymatic Ti change: at 40-60 ℃ polyphenol oxidase catalyzed reaction of phenolic compounds to form Ti color, which is a secondary coupling reaction.
