Bloom is a test used to measure the strength of a gel, most commonly gelatin. The test was originally developed and patented in 1925 by Oscar T. Bloom.[1] The test determines the weight in grams needed by a specified plunger (normally with a diameter of 0.5 inch) to depress the surface of the gel by 4 mm without breaking it at a specified temperature.[2] The number of grams is called the Bloom value, and most gelatins are between 30 and 300 g Bloom. The higher a Bloom value, the higher the melting and gelling points of a gel, and the shorter its gelling times.[2] This method is most often used on soft gelatin capsules ("softgels"). To perform the Bloom test on gelatin, a 6.67% gelatin solution is kept for 17–18 hours at 10 °C prior to being tested.
Various gelatins are categorized as "low Bloom", "medium Bloom", or "high Bloom", but there are not universally defined specific values for these subranges. Gelatin is a biopolymer material composed of polypeptide chains of varying length. The longer the chain, the higher the Bloom number:[3]
| Category | Bloom number (Bloom strength) | Average molecular mass | Examples |
|---|---|---|---|
| Low Bloom | 30–150[4] | 20,000–25,000 | Beef hide low Bloom gelatin (USP-NF)[5] |
| Medium Bloom | 150–225 | 40,000–50,000 | Gelatin type B[6] |
| High Bloom | 225–325 | 50,000–100,000 | Gelatin type A[6] |
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