Hygroscopic substances storage

The storage condition of raw materials, particularly hygroscopic substances, is important, and as a minimum water activity (Aw) of 0.70 is required for osmophilic yeasts, 0.80 for most spoilage moulds and 0.91 for most spoilage bacteria, precautions should be taken to ensure that dry materials are held below these levels. Some packaging used for raw materials, such as unlined paper sacks, may absorb moisture and may itself be subject to microbial deterioration and so contaminate the contents. For this reason polythene-lined sacks are preferable. Some liquid or semi-solid raw materials contain preservatives, but others such as syrups depend upon osmotic pressure to prevent the growth of os-mophiles, which are often present. With this type of material it is important that they are held at a con-... 

The substance should be unaltered in air during weighing this condition implies that it should not be hygroscopic, oxidised by air, or affected by carbon dioxide. The standard should maintain an unchanged composition during storage. 

Comments most substances sold as sodium bisulfite contain significant, variable, amounts of sodium metabisulfite, as the latter is less hygroscopic and more stable during storage and shipment. See Section 18. 

Hygroscopicity is the ability of solids to adsorb water onto their surfaces microscopically. The rate of adsorption and the equilibrium amount of water adsorbed depend on the relative humidity of the atmosphere. For solid substances, it is important to learn if the material under study is hygroscopic. Thus, steps into drying and storage, such as humidity control in the production and packaging environments, may have to be established to avoid manufacturing difficulties and instability problems. 

HMIS Health 1, Flammability 0, Reactivity 0 Storage Hygroscopic store in a cool, dry, well-ventilated area away from incompatible substances... 

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