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　　Soft and tender.Tofu has a fine, delicate texture, strong water retention, good elasticity, bright cut surface, stable formation, beautiful color, porous and soft when cooked, making it suitable for various cooking methods.This unique feature is determined by a series of processing techniques.

Method 1. Soybean selection.Because the pigment in the seed coat affects the color of the tofu, select plump yellow soybeans. Premium varieties are peeled before processing to ensure good color.Secondly, use green or double-colored (purple-spotted) soybeans.Do not use other colored-seeded soybeans.

2. Soaking.The quality of soaking directly affects the quality of soft tofu.Soybeans must be thoroughly washed to remove impurities and dust before soaking.Different types of soybeans absorb water at different rates, expand at different speeds, and require different soaking times in winter compared to other seasons.The following table shows general soaking time and extent:

Season

Temperature (°C)

Water Temperature (°C)

Soaking Time (hours)

Soaking Degree

Winter

0

0

20～22

　　Bean cakeCentral part of the bean cake has a 1/10 yellow depression.

Early winter-spring

10

10

12～14

Central part of the bean cake has a 1/10 to 1/15 yellow depression.

Spring-autumn

24

20

10～11

Central part of the bean cake has a 1/5 yellow depression.

Summer

30～40

25～30

6～7

Central part of the bean cake has a 3/10 yellow depression.

During soybean crushing, heat is generated causing protein denaturation and reduced viscosity,Proteinquality changes. Inadequate soaking results in low viscosity,Milkand poor setting properties. For soft tofu, minimal dehydration is required during shaping.

Thus, the soaking time should be shortened slightly while the expansion level should be slightly less than for other varieties.Proper soaking ensures fine and tender texture, strong water retention, good elasticity, bright cut surface, porous structure, and soft firmness. It also does not reduce yield; in fact, it may increase it.Insufficient soaking leads to lower protein extraction rate and reduced yield with poor quality.Over-soaking results in high protein extraction but excessive acidity reduces viscosity, resulting in loose structure and poor water absorption. Quality is poor.

3. Making milk.(1) Crush the soybeans into a paste.Coarse paste leads to lower protein extraction rate.Too fine paste mixes with bean residue, reducing product quality.General consistency for grinding paste: 70～80 mesh.Mesh size of cloth or nylon bag: 140～150 mesh.(2) Add boiling water.Total amount of water is nine times the weight of dry beans, with some variations depending on whether it's ordinary soft tofu or Hubei-style tofu (8 times).Excessive water dilutes milk concentration, leading to loose setting structure and poor texture.

Insufficient water results in high concentration, less water absorption, strong protein coagulation. Both cases lead to coarse, hard, and broken texture when eaten.(3) Milk must be boiled within 10 minutes at over 92°C for complete denaturation of proteins and full setting.Inadequate boiling results in incomplete denaturation and setting leading to soft tofu that may disintegrate easily and turn red in color.Uncooked milk contains saponins and protease inhibitors, which can cause digestive issues or poisoning upon consumption.(4) Quick cooling after initial boiling followed by adding curdling agent leads to slightly firm texture.Low temperature results in incomplete setting and a watery structure that requires further dehydration before making tofu. This is neither young nor mature, and not suitable for soft tofu.Ideal milk temperature: 75°C for optimal setting.

4. Setting operationRiceChalk slurry must be prepared properly to ensure good quality. Main key point: use chalk slurry made from grinding chalk with a small amount of soy milk until fully mixed and thickened, usually taking about one hour.

Mixing too slowly can affect setting effect.Proper consistency for chalk solution: 8%. Use white transparent fiber chalk to achieve neat and strong structure.Other types are not as effective.

(2) Correct angle during pouring.RiceThe unique characteristics of Nanjing soft tofu mainly come from the use of proper pouring technique, which ensures good setting results.Five critical factors: (1) Chalk slurry must be freshly prepared by grinding chalk with a small amount of soy milk until fully mixed and thickened.Consistency should not be too thin to prevent dilution. It takes about an hour to prepare the chalk slurry.Quickly and tightly mixing is crucial; if done slowly, the chalk will swell and affect setting quality.After preparing, dilute the chalk solution with water, removing coarse particles to a 8% concentration.Choose white transparent fiber chalk for strong structure.Other types are less effective.(2) Correct pouring angle.

Pour the chalk and soy milk mixture (slurry) at a 15～35° angle against the side of the container, ensuring a steady flow directly to the bottom. This allows proper mixing with the milk, leading to good setting results.If less than 15°, some slurry will spill out, reducing effectiveness.Angles between 40～50° result in splashing and uneven mixing, leading to poor structure.Higher angles further reduce effectiveness.For soybeans weighing less than 7.5 kg, pour the slurry into the container first, then pour the milk directly for better results.

(3) Chalk dosage: about 2.4～2.6% of dry bean weight.

Insufficient chalk leads to weak protein bonding and incomplete setting.Excessive chalk causes too rapid bonding leading to loose structure with poor water retention, resulting in over-setting.(4) Proper pouring force is crucial even when the angle and chalk dosage are correct.

Low pressure results in slow milk mixing and quick setting in lower layers, causing over-setting while upper layers remain under-set.High pressure causes rapid mixing preventing proper setting time leading to failure.Ideal result: initial setting achieved within 40～50 seconds after pouring ends. This ensures optimal setting without compromising yield or quality.

(5) Adequate resting period of about 30 minutes is necessary for full setting and structural stability.Shorter times lead to weak structure, while longer times result in over-setting and reduced flexibility.For soft tofu, longer rest time ensures adequate setting without excessive hardness or brittleness.

Improper settings reduce yield by 10～15% for under-set and 10～20% for over-set products.Because, although the soy milk has initially coagulated, protein denaturation and bonding are still ongoing, and the tissue structure is still forming.For soft tofu production, since it does not require dehydration, the static time needs to be longer; this is why.If the resting time is too short, the structure will be weak, leading to quick dehydration, making the soft tofu lose moisture and become less fine and lustrous, instead becoming coarse and hard.If the resting time is too long, the coagulated material cools down, reducing its cohesion; without dehydration, the soft tofu becomes overly delicate, easily breaking during handling, affecting its shape stability and usability.

Tofu produced with incomplete or excessive coagulation has poor quality and low yield. Incomplete coagulation yields a 10-15% reduction in output, while excessive coagulation results in an even greater 10-20% decrease.