In the practice of biscuit production, the problem of cracking of biscuits is often encountered, and the cracking of biscuits due to external pressure or impact is customarily called abnormal rupture. This rupture is generally caused by external factors such as human factors and mechanical factors. Caused by the cause. Due to the rapid cooling of the biscuit, the internal stress is generated by the unbalanced stress, which is called the natural crack. This crack is mostly caused by the internal factors of the biscuit, and the influencing factors are more.
Generally speaking, abnormal cracking can be reduced or solved by strengthening management and improving packaging. However, the handling of natural cracking problems is complicated, which is a big problem that has been plaguing the biscuit industry. One of the reasons for the decline in benefits. Therefore, this article explores various factors affecting the quality of biscuit cracking and how to prevent and control it.
First, the factors affecting the cracking of biscuits
1, cooling ambient temperature
In actual production, cracking of biscuits is often found to be particularly severe at lower ambient temperatures. The study found that the cracking of the biscuit has a significant relationship with the cooling temperature. As the temperature decreases, the cracking rate increases significantly and has broken in a short time.
In general, the effect of ambient temperature on the cracking of biscuits has two aspects, the first is thermal shock, and the second is the excessive spread of moisture. When the biscuit is baked, the surface temperature is as high as 180 °C. When the temperature is lower than 15 °C, the temperature difference is as high as 160 °C. The biscuit is cooled rapidly, the surface moisture is rapidly evaporated, and the internal moisture is rapidly moved to the outer layer under the force of heat. Strong heat exchange and water volatilization cause strong stress inside the biscuit to change the relative position of the solid particles inside the biscuit. This deformation increases with time. When the deformation reaches a certain level, the combination of the biscuit itself has been Without this deformation, the cracks in the biscuit.
It has been observed that cracks in biscuits tend to start from the middle and then expand outward until the biscuit breaks, and cracks can be found on the 2nd day of production; in low temperature and low humidity, cracks can be found in 5 hours.
2, baking time and temperature
The baking process of biscuits is divided into four stages: expansion, shaping, dehydration and coloring. The dehydration phenomenon always runs through the whole baking process. In the early stage, the free water and the adsorbed water are mainly excluded, and the combined water is excluded in the later stage; the temperature of the combined water evaporation does not need to be too high, but it takes time, if the mesh belt rotates too fast, and the furnace temperature Too high, the moisture outside the biscuit is quickly drained, and the internal moisture is not completely removed, resulting in a difference in moisture inside and outside the biscuit. The extreme moisture gradient changes rapidly under thermal shock, and the biscuit is easily broken. Some scholars have found that the average furnace temperature is At 210 ° C, baking for 3 min, the natural rupture rate of biscuits is as high as 94.6%; baking is more than 5 min, the average furnace temperature is 176 ° C, the rupture rate is only 2.8%, the moisture content of biscuits decreases with the extension of baking time, and the natural rupture of biscuits The rate is also decreasing.
3, the amount of grease
It is found that the self-cracking rate of biscuits increases with the increase of oil dosage. When the value reaches a certain value, the self-cracking rate is the largest, and then the self-cracking rate decreases with the increase of the amount of oil, until it is zero. As the amount of oil increases, the gluten becomes broken and normal, and the toughness and elasticity are lowered.
On the palate, the finished biscuits are changed from tough and crispy to crispy. During the dough formation process, the gluten protein absorbs water and swells, and the water absorption can reach 150% to 200%. The more gluten is formed, the more water is formed, the more difficult it is to remove during baking, and the moisture imbalance inside and outside the biscuit is easily caused. The protein molecules lose their moisture during the baking process and agglomerate and deform until they are denatured.
About 25% of the amylose in the flour is also agglomerated and deformed due to water dispersion. When the improper baking causes the phenomenon of "uncooked outside the coke", the above agglomeration will continue to occur during cooling. At this time, since the shape of the biscuit is basically fixed, the aggregation phenomenon will generate a large stress.
The dried biscuits are a brittle material that lacks the properties of crack resistance. If there is no scar, it is very hard, and once there is a crack, it is easy to break. Although the presence of gluten can increase the crack resistance of the biscuit, it is the internal cause of the cracking of the biscuit. When the gluten fibers are arranged in a network, the crack resistance is strong, and when the dough is aligned due to the excessive calendering ratio, the self-cracking is more likely to occur.
As a result of observation, it was found that too many cracks and calendering directions were uniform, that is, in the same direction as the gluten fibers.
In summary, when the amount of oil is small, the gluten is formed more and the quality is better, which increases the crack resistance of the biscuit, and its strength is sufficient to resist the stress generated inside. When the amount of oil is large, although the crack resistance of the biscuit is low at this time, the stress generated by itself is small, so it is not easy to cause self-cracking. Only when the amount of oil is not too much and not too little, the stress generated inside the biscuit is large, and the crack resistance is small, so it is most likely to cause self-cracking.
4, sugar consumption
The cracking rate of the biscuit decreased with the increase of the amount of sugar. The gluten was broken and the viscosity decreased with the increase of the amount of sugar. On the taste, the biscuit became more and more hard and brittle. Due to the strong anti-hydration effect of the sugar, the formation of gluten in the dough is reduced, thereby reducing the chance of internal stress, and the gelation of the sugar improves the crack resistance of the biscuit. Therefore, the cracking rate of the biscuit decreases as the amount of sugar increases.
5, the design of the mold
The mold generally has pinholes and patterns. The pinholes are good for the release of the leavening agent gas and water vapor. If the pinholes are designed to be too wide, the water vapor is difficult to exclude evenly, and the cracks are more. If the pinholes are too dense, the gas is too fast to be excluded. It will affect the bulkiness of the biscuits. Practice tells us that an average hole per 2.5 square centimeter is better, and the flatness and rupture rate of the biscuit are better improved.
Second, the prevention and control measures of biscuit cracking
1, cooling ambient temperature
There are two solutions to the cracking of biscuits caused by low cooling ambient temperature. - If the conditions permit, extend the length of the cooling line as much as possible, and appropriately increase the temperature around the cooling line to prevent temperature and humidity conditions. The mutation causes residual stress. Secondly, a cover can be added to the front of the cooling line, and the cooling fan can be turned off to suppress the evaporation speed of the water, which plays an active role in preventing the biscuit from cooling too fast and avoiding self-cracking.
2, baking time and temperature
Reasonable adjustment of the temperature of the "bottom fire" and "face fire" in the oven during the baking process is the key to preventing the cracking of the biscuit. Generally speaking, in the front temperature zone, the "bottom fire" temperature should be appropriately increased, the "face fire" temperature should be lowered, the cake blank carrying mold should be heated rapidly to ensure the uniform expansion of the cake blank; the medium temperature zone should appropriately raise the "face fire" temperature. Correspondingly reduce the "bottom fire" temperature, so that both sides of the cake are in a high temperature state, in order to facilitate the evaporation of moisture inside the cake blank. In the final temperature zone, only part of the "face fire" temperature can be retained, the "bottom fire" can be eliminated, and the cake blank can be used to carry the mold. The heat is heated on the underside of the cake until it is baked.
3, the amount of oil and sugar
In view of the cracking of biscuits caused by the amount of raw materials, our general solution is to rationally design the formula, avoid sensitive critical points, improve the surface process, ensure that the dough gluten forms a network, and ensure a reasonable calendering ratio per roll during molding. The dough has self-regulating later time and so on.
4, the mold
Regularly inspect and clean the cake carrier mold to keep the mold clean, the needle height is moderate, prevent the pinhole on the cake blank from being penetrated, and the gas permeability of the cake blank can not meet the requirements. During the baking process, the cake is kept. The carrying mold of the blank is arranged in a "human" shape, which is beneficial to the flat shape of the biscuit and the expansion of the biscuit. At the same time, the "human" type has a high heat capacity, and is also beneficial for the slow cooling of the biscuit after baking.
Third, the conclusion
Cracking of biscuits is a comprehensive problem involving food chemistry, thermodynamics, materials science and production management. Can not be solved from a single aspect. Practice has shown that it is necessary to comprehensively consider the above factors to better suppress the cracking of biscuits.
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