Frozen dough is undoubtedly a breakthrough success in the field of modern baking. It has greatly changed the production and supply of baked goods and brought greater development opportunities to the entire baking industry.

Today, let us explore the principles behind frozen dough and the key factors that affect its quality and effect.

What exactly is frozen dough? How does it work? What factors will have an important impact on it? Let us unveil this mysterious veil together. (Reading to the end of the article will definitely give you a deeper understanding of frozen dough)

01 What is frozen dough

Frozen dough is a dough or semi-finished bread product obtained by interrupting a certain process in the normal production process of bread, which is rapidly frozen (below -30 degrees) and then stored in a stable environment of -18 degrees, and then thawed before being shaped.

02 Classification of frozen dough

1. Pre-divided frozen dough → directly divided and frozen after leaving the cylinder.
2. Pre-shaped frozen dough → directly shaped and frozen after dividing.
3. Pre-fermented frozen dough → directly frozen after forming and fermenting.
4. Pre-baked frozen dough → frozen after fermentation and baking. According to the above four categories, pre-divided frozen bread is more suitable for the production process of most bakeries, so we will analyze the pre-divided frozen dough in depth.

03 The principle of frozen dough

The principle of frozen dough is to use the effect of ice crystals. By rapidly cooling the dough, the water in the dough is rapidly crystallized to form ice crystals. As the temperature decreases, the number of ice crystals increases and finally reaches a frozen state.

The free water in the intercellular space of the dough and the bound water in the cells are simultaneously frozen into countless crystals. Because the dough is cooled quickly due to rapid freezing, the ice crystals are small and evenly distributed, and the dough structure is not significantly damaged.

04 The first-factor affecting frozen dough

The first factor affecting frozen dough is the temperature of the freezing equipment. Frozen dough generally chooses the post-yeast method, so that the yeast will not become active quickly. The temperature out of the cylinder is between 18 and 20 degrees. It is quickly divided and kneaded for rapid freezing.

The rapid freezing temperature is minus 30 to 40 degrees, so that the center temperature of the dough quickly drops to minus 10 to 15 degrees, and then it is transferred to a stable environment of minus 18 degrees for storage. 

Why should it be placed in an environment below minus 30 degrees for rapid freezing? Can’t it be directly placed in a -18-degree environment? The answer is: Of course not. Because in an environment of -18 degrees, it takes about 60 minutes for the center temperature of the dough to drop to minus 15 degrees, during which a lot of ice crystals will be produced. But in an environment below minus 30 degrees, it takes about 20-30 minutes for the center temperature of the dough to drop to minus 15 degrees, and the ice crystals produced will be relatively few and small.

05 Why do ice crystals destroy the dough?

Ice crystals are crystals formed when the liquid in the dough is frozen into ice during the freezing process. The formation of ice crystals in the dough can cause serious damage to the gluten network structure and yeast cells of the dough.

The main reasons for this are: When the free water in the dough turns into ice, the volume increases by about 10%. The physical changes destroy the gluten network structure and the microstructure of the yeast cells, and the ice crystals produced will take away the water in the dough to increase the volume. 

The size, quantity, shape, and position of the ice crystals will cause different degrees of damage to the dough tissue.

06 Factors affecting ice crystals

1. Freezing temperature and speed 

Crystals grow in the temperature range of -1℃ to -5℃, which is technically called the “maximum ice crystal formation temperature range”. When the dough is in the temperature range of -1℃ to -5℃, the ice crystals grow the most, and almost 80% of the water in the dough will be converted into ice crystals. In the temperature range of -1℃~-5℃, the longer the stay time, the larger the ice crystals, and the greater the damage to the dough.

The temperature at which the dough freezes fastest (ice crystals are not easy to grow) is about -40℃, and commercially available frozen dough is usually quickly frozen at -35℃ or lower. However, many stores only use freezers with a minimum temperature setting of -18℃ to slowly freeze the dough. 

Slowly frozen dough needs to pass through this ice crystal zone for a long time, resulting in a fast growth rate of ice crystals and a larger volume of ice crystals, which will damage the gluten network structure more seriously. 

At the same time, the volume of yeast cell fluid expands and increases, accelerating the death of yeast, so that the expansion rate of the dough after thawing will be affected. (Defrosting process in different environments)

2. Water content inside the dough

The frozen dough should control the amount of water added and be quickly frozen at low temperatures to prevent quality changes during freezing. If the water in the dough tissue is unevenly distributed, it will also cause damage to the dough, so the ice crystals must be kept as small as possible and the water content must be homogeneous.

3. Storage conditions of the dough 

Even if quick freezing produces fine ice crystals, the ice crystals will grow larger during storage. This phenomenon is called “ice crystal recrystallization.” During frozen storage, slight water movement occurs, which is closely related to the recrystallization of crystals, the generation of frost, and the drying of the dough surface. 

When the storage temperature is high or the temperature changes, this water movement will accelerate. Therefore, in order to prevent recrystallization, it must be stored at the lowest possible temperature and avoid temperature changes during storage. 

In addition, if the freezing speed is too fast, it will also cause the bread yeast to freeze in the body, and the yeast will be more likely to die, so the speed of freezing the dough should be controlled at the fastest speed within this range where the yeast will not die. The standard speed is the cooling speed of the center temperature of the dough in the freezer, and the cooling speed is 1~2℃ per minute.

07 How to reduce the occurrence of ice crystals?

1. Selection of flour: Freezing will weaken the binding force of gluten, resulting in poor expansion rate. Use super high-gluten flour with a protein content of about 13% to 14%. 
2. The water content in the dough reduces the amount of free water in the dough, usually reducing the water content by 5% to 10% from the formula. 
3. The content of fat and sugar in the dough. When the amount of fat and sugar reaches a certain amount, the frost resistance of the dough can be improved. Therefore, when making frozen dough, you must control the temperature and reduce the formation of ice crystals. The shorter the time for ice crystals to be generated, the less damage to the dough.

08 Common yeast in making frozen dough

Yeast is the soul of bread, and the quality of the yeast directly affects the effect of the final product. For frozen dough, due to the addition of freezing and thawing processes, the living environment of the yeast in the dough changes, which puts higher requirements on the quality of the yeast. 

Classification of yeast: *Liquid yeast *Fresh yeast *Crushed yeast *Semi-dry yeast *Instant dry yeast *Active dry yeast Usually the yeasts we commonly use are dry yeast, semi-dry yeast and fresh yeast: dry yeast has good fluidity and is easy to use. 

Preservation, storage at room temperature, and long shelf life. Fresh yeast has high activity, fast fermentation time, and refrigerated storage, and the bread made has good flavor. Semi-dry yeast is between dry yeast and fresh yeast. It has the advantages of both dry yeast and fresh yeast.

 It has the same fermentation flavor as fresh yeast and develops quickly, and has the same fluidity as dry yeast, which is easy to weigh and has a long shelf life when frozen. 

Since semi-dry yeast is routinely stored at -18°C, fresh yeast is more resistant to freezing than dry yeast, so semi-dry yeast is usually used first when making frozen dough. Yeast is very sensitive to temperature changes: * dormant in 0-4℃ environment * semi-dormant in 10℃ environment * yeast is very active in 20℃-45℃ environment * yeast loses activity in environments above 50℃-55℃ 

09 Freezing is harmful to yeast Yeast

It is very “anti-freeze”, and low temperature will not affect the fermentation ability of the yeast. The fresh yeast we often use is stored refrigerated, and frozen yeast can be stored at minus 18°C for up to 2 years. What affects the yeast is the dough being chilled. Frozen dough inevitably involves “freezing” and “thawing” processes. 

The “ice crystals” produced during the rapid freezing process will destroy yeast cells and affect yeast activity. 

Changes in dough temperature and freezing speed during the freezing process will also affect yeast activity, causing various consequences: *Long rising time for the dough *Insufficient gas production of the dough *Dough resting *The volume of the finished product is reduced between minus 3°C and minus 12°C When the temperature is high, the water inside the yeast cells freezes, and the degree of cell damage depends on the length of time at this temperature. 

Therefore, when controlling the recipe process, the process must be strictly controlled. Over-freezing or under-freezing will cause great harm to the yeast. At the same time, it is also necessary to ensure that it can quickly pass through the 5°C to minus 5°C safe zone.

10 The impact of osmotic pressure on yeast

The water crystals in frozen dough also have a great impact on it. The osmotic pressure of the dough increases and yeast dissolves in it. 

The osmotic pressure generated is enough to destroy the cell membrane of the yeast.

 If the concentration inside and outside the yeast cell membrane is equal and the osmotic pressure is 0, the yeast cell can maintain its normal shape. But when the balance of osmotic pressure is broken, the water in the yeast cell membrane will penetrate to the outside, and the yeast cell will rupture.

 The activity of the yeast itself will be affected, and it will also affect the final proofing. Therefore, a suitable yeast must not only be “freezing resistant” but also work hard to overcome the influence of osmotic pressure. 

Through experiments, we found that the natural trehalose, glycerol amino acids (including proline) and some small molecule sugars (glucose, maltose) contained in the yeast itself are very important for the yeast to maintain activity. 

Especially for natural trehalose, you can only choose “elite soldiers” with high bacterial content for cultivation. The artificial addition of trehalose cannot improve the activity of yeast.

11. Control of key influencing factors

Strictly control the freezing speed: 

1. Slow freezing (0.1°C/min) will generate large ice crystals, which will form larger ice crystals and damage yeast cells and gluten proteins 
2. Rapid freezing (1°C/min) Less crystallization will be produced, which is a more suitable rapid freezing speed. 
3. Extremely rapid freezing (10°C/min) will produce small ice crystals, which will easily aggregate into large ice crystals during thawing, destroying the gluten network.

Select freezing temperature: different freezing temperatures will have different effects on the dough, and the quick freezing temperature must be adjusted according to the formula and process. For example, when making Danish bread dough, when the freezing temperature drops from minus 25°C to minus 40°C, the shelf life of the dough will be shortened by more than 60%.

Control the storage process: 

During the freezing (minus 18 degrees Celsius) storage process of frozen dough, the gluten network, and yeast cells in the dough continue to be damaged, and the quality of the dough also declines as the shelf life is extended. Storage temperature changes have a great impact on the quality of frozen dough. 

Control the thawing process: 

Proper thawing methods for frozen dough can mitigate and reduce the damage caused by ice crystals to yeast cell membranes and gluten proteins during thawing. This can shorten the proofing time of the dough and improve the volume of the bread.

12 Freezing Process

• Try to shorten the time between dough mixing and rapid freezing, and maximize the restriction of fermentation before freezing, which can effectively extend the shelf life of frozen dough. Because the yeast in the fermented dough is in an active state, it is easy to cause great damage during the rapid freezing process, affecting the later rise of the dough.
• According to the sugar and oil content in the dough, as well as the weight and size of the dough, adjust the freezing time to control the center temperature of the dough.

13. Thawing process

● Refrigerated thawing (0-4℃):

 The ice crystals will dissolve to very small sizes, which will slow down the impact of freezing on the dough and make it rise more evenly. 

● Room temperature thawing (20-25℃): 

The surface and internal thawing speeds are different, and there will be a lot of moisture on the surface. 

● Proofing box (30-38℃): 

The surface and internal thawing speeds are different, the yeast activity is different, and the quality of the finished product is poor.

14. Yeast selection

● Fresh yeast: 

has the highest activity, but needs to be stored at 0-4℃ and has a shelf life of only 45 days. Therefore, fresh yeast can be given priority in areas with convenient logistics. ● Dry yeast: Suitable for areas where the supply of fresh yeast is inconvenient. Dry yeast combined with frozen dough improver can meet the needs of frozen dough products with a short shelf life of about one month. 

● Frozen yeast:

 It can be stored for 24 months at minus 18°C. It is more suitable for areas where fresh yeast is not available. All the above measures are to achieve two purposes: 

●Prevent osmotic pressure from damaging yeast cells 

●Prevent ice crystals from puncturing the yeast cell membrane. 

Only by doing these two things can the yeast in the frozen dough maintain good activity and show good performance during the shelf life. Good fermentation rate After understanding yeast, we know that it is not that yeast is not “anti-freeze”, but that the water in the dough forms ice crystals and affects the vitality of the yeast. At the same time, the rapid freezing process will also destroy the protein structure, resulting in prolonged dough-proofing time and dough collapse. So how to improve this phenomenon?

15 The key element of frozen dough – improver

When making frozen dough, the rapid freezing process will cause great damage to the yeast and protein in the dough, so frozen dough improver is used to alleviate and improve these problems. Reasonable use of improvers in frozen dough can: 

• Improve the mechanical operability of frozen dough
• Increase the strength and endurance of the dough, and improve the volume and structure of the bread 
• Improve the water retention function of the dough and reduce the damage caused by ice crystals in the dough 
• Protect and extend the shelf life of frozen dough
• Optimize dough gas retention during thawing and proofing processes 

Different types of freezing improvers are suitable for various bread product applications, such as staple bread and sweet bread, and the use of improvers also varies differently. In actual production, different improvers need to be selected according to different products and application production conditions.

Generally speaking, adding 1.5%-3.0% improver to frozen dough can significantly improve the baking effect of frozen dough, extend the shelf life of frozen dough, shorten the dough rising time, strengthen the dough structure and increase the bread volume. What ingredients make improvers so powerful? Generally speaking, improvers mainly include the following main ingredients :

16 Improvers suitable for frozen dough

● Long-lasting and stable type

1. Improve the ductility and fermentation durability of the dough, improve the fermentation endurance, and prevent collapse.
2. Suitable for short-term frozen dough products (freezing period <1 month), more suitable for Danish, croquettes and hamburger products.

 ● Frozen dough type

1. Dedicated to frozen dough, strengthen the dough network protection, protect flour protein, and improve the volume of bread 
2. Improve the dough’s frost resistance, avoid the formation of a large number of ice crystals, and extend the shelf life of frozen dough. Therefore, we must choose the type of improver according to our own needs, and then combine it with the yeast type that suits us, store the dough in an appropriate manner, reduce the damage of ice crystals to the dough, and will definitely make high-quality frozen dough.

A spiral freezer has a spiral conveyor system which allows for continuous freezing while occupying a minimal footprint. The compact, multi-level design enables the spiral freezer to optimize vertical space, which is particularly beneficial for facilities with limited floor area.

The spiral conveyor belt moves the dough at the freezing chamber of -35℃, ensuring that they are frozen quickly and uniformly. It can freeze the dough quickly in 30 to 40 minutes.

The belt utilizes a modular plastic belt to prevent the belt marks from being on the belt.

For the working principle of a spiral freezer, please visit the video

https://www.youtube.com/embed/3mtWAS3PzBA?si=jc16L_2WlHrwzGTe