Before boiling, the medicine should be soaked in water in advance. This is because most herbal medicines are dry and have a certain volume and thickness. They must be soaked in cold water at room temperature before boiling. The purpose is to make the herbal medicine moist and soft, expand the cells, and dissolve the active ingredients in the herbal tissue first, generating osmotic pressure so that the active ingredients can permeate and diffuse into the water outside the herbal tissue. At the same time, it can avoid the coagulation of proteins in the herbal tissue and the gelatinization of starch, making it difficult for the active ingredients to seep out. The antibacterial experiment of Euphorbia helioscopia soup on Staphylococcus aureus has shown that the diameter of the antibacterial zone of the first decoction after soaking for 20-30 minutes is 17 mm, and the diameter of the second decoction is 15 mm, while the diameter of the antibacterial zone of the first decoction without soaking is 15 mm, and the diameter of the second decoction is 14 mm, which means that the first decoction without soaking can only achieve the efficacy of the second decoction after soaking. Therefore, the herbal medicine should be soaked in cold water before boiling.
The soaking time should be determined according to the nature of the herbal medicine. Generally, for compound preparations mainly composed of herbs, leaves, stems, etc., the soaking time can be 20-30 minutes, while for herbs mainly composed of roots, rhizomes, seeds, fruits, etc., the soaking time can be 60 minutes. However, the soaking time should not be too long to avoid enzymatic degradation and mold spoilage of the medicine.
The amount of water added in the decoction is a very important issue, and the amount of water directly affects the quality of the decoction. If there is too much medicine and too little water, it will result in "incomplete cooking and incomplete decoction". The active ingredients are not fully extracted, and the medicinal juice will dry up as soon as it evaporates slightly, and the active ingredients of the medicine may be destroyed due to local high heat; if there is too little medicine and too much water, although it can increase the amount of active ingredients dissolved, the volume of the medicinal soup is too large and it is not suitable for patients to take.
Herbal medicines have different textures and different water absorption capacities. Generally, the water absorption capacity is 5-10 times the weight of the medicine, and for some, such as Althaea officinalis, it can reach 20 times. Therefore, the amount of water used in decoction should be determined according to the dosage and texture of the medicine. For medicines with the same weight, those with lighter texture will have larger volume and greater water absorption capacity, while those with solid texture will have smaller volume and less water absorption capacity. For flowers, leaves, whole plants and other medicines with a relaxed texture, the amount of water used should be greater than the general amount of water. For minerals, shells and other medicines with solid texture, the amount of water used should be less than the general amount of water.
According to traditional experience, put the herbal pieces in the decoction pot, add water to exceed the surface of the medicine by 3-5 cm, and the second decoction can exceed the surface of the residue by 1-2 cm. This is a convenient and easy-to-master method of adding water.
Calculate the amount of water added based on approximately 10 mL of water per gram of herbal medicine, and then add 70% of the calculated total amount of water to the first decoction, leaving the remaining 30% for the second decoction.
The amount of water used should be determined based on the length of the decoction time, the amount of water evaporation, the water absorption capacity of the herbal medicine, and the desired amount of medicinal juice obtained.
Therefore, the amount of water added should be determined based on the length of the decoction time, the amount of water evaporation, the water absorption capacity of the medicine, and the desired amount of medicinal juice obtained.
Some researchers have studied the calculation formula for the amount of water added in the decoction:
Q = W × K + R + T × V
Where Q is the amount of water added
W is the weight of the original medicine
K is the water absorption capacity
T is the decoction time
V is the evaporation rate of water per unit time
R is the amount of medicinal juice obtained
Using the above formula to calculate the amount of water added is a cumbersome task. First, a large number of experiments need to be conducted to determine the water absorption capacity of each type of herbal medicine, and then list them for future use; second, the measurement of V value is meaningful only under the condition of constant heating firepower during the decoction. Experimental results have shown that an average evaporation rate of 15-20 mL per minute is generally applicable. However, it must be operated in a certain container and at a certain temperature. If the conditions change, the calculated Q value becomes meaningless. Therefore, the above calculation formula is only applicable to units with a large amount of decoction business.
The amount of decoction should be determined based on the total amount of medicine. Generally, the more medicinal juice obtained, the higher the yield of the decoction. However, the amount of medicinal juice is limited by the dosage, so a reasonable limit needs to be determined. Based on experimental data, it has been determined that when the amount of medicinal juice is 1:4, the two decoctions can achieve a yield of 70% to 80%. If this amount of liquid is further concentrated to 1:2, it will be easier for patients to take.
A research institution conducted 87 stove-fired decoctions, recorded the actual amount of water used, and used statistical methods to calculate the correlation coefficient between the weight of the medicine and the amount of water consumed, and obtained the following calculation standards for the amount of water used:
First decoction = 100 mL × weight of medicine (liang) + 150 mL + dosage
Second decoction = dosage + 200 mL
This calculation formula is suitable for weighing 1-8 liang of medicine and direct heating decoction. The heating time is about half an hour. When the water absorption rate of the medicine is too high or the heating firepower during decoction is too high or too low, the amount of water added can be increased or decreased according to the specific situation.
The dosage required by clinical physicians is generally between 150-300 mL, and it should be reduced for children.
