How to preserve birch for a long time
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1. Birch sap contains a wealth of sugars, proteins, and other nutrients, which are easily contaminated by microorganisms, leading to spoilage. To preserve the sap within a short time after harvest, simple ice cellars or basements with shaded shelters filled with snow and ice can be used. At temperatures not exceeding 5℃, the sap can be kept fresh for 3-5 days. The material buckets must be cleaned and disinfected after each use. To prevent the oxidation and discoloration of VC and tannins, it is essential to seal with paraffin.
2. Due to the low dry matter content in birch sap (usually between 0.5-1.2%), and because the collection areas are all in forest regions, this brings certain difficulties to storage, transportation, and utilization. Jiang Desen, Wei Ziyu, Li Qingsheng, and others have conducted research on the concentration process of birch sap. After multi-stage filtration, the birch sap is concentrated in a vacuum concentration pot to produce concentrated birch sap with three specifications of dry matter content: ≥3%, ≥6%, and ≥9%, which is convenient for the storage and transportation of birch sap.
3. Using natural white birch sap as the material, the contaminated microorganisms were isolated, cultured, and preliminarily identified, and it was found that there are different amounts of bacteria, yeasts, molds, and actinomycetes in natural birch sap and its beverages. Among them, molds are the most common, followed by yeasts, bacteria, and the least actinomycetes. Based on the distribution of contaminated microorganisms, several methods to control and inactivate microorganisms were compared. The acidic treatment at pH 2.0 failed to inactivate all contaminated microorganisms, while using the 90℃ heat sterilization method or membrane filtration technology can achieve ideal results. Chen Tieshan and Zhang Yuanmin added a small amount of sodium benzoate (1g/kg) to the inspected birch sap, then added citric acid (1.5g/kg) to adjust the acidity to pH ≤3.5, and then added ascorbic acid (0.1g/kg) and sodium bisulfite (0.1g/kg) in proportion, which can achieve a good preservation effect and can be stored at room temperature for 6 months. Huang Wenzhe and Wang Jianhua found that adding a single preservative sodium benzoate to birch sap is less effective than using a compound preservative. Adding preservatives in the ratio of benzoic acid 0.03%, ethyl p-hydroxybenzoate 0.03%, and sorbic acid 0.05% results in a lower amount of preservatives used and a reliable preservation effect.
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