Buttermilk: why 227 g per cup is wrong
King Arthur publishes 227 g per US cup of buttermilk. This site rejects that figure and publishes 245 g instead, from USDA FoodData Central (density 1.0355 g/mL, matching the composition of the substance). The reason:
227 g/cup implies a density of 0.9595 g/mL, less than water. Cultured buttermilk is roughly 90% water plus milk solids (protein, lactose, minerals) all denser than water. The mixture must be denser than water, not lighter. King Arthur's figure appears to be their fluid-oz convention rather than a bench measurement; the same pattern rejected on milk, yogurt, heavy cream, Greek yogurt and pumpkin purée applies here.
The arithmetic
| Source | 1 cup | Density | Status |
|---|---|---|---|
| King Arthur | 227 g | 0.9595 g/mL | Rejected on physics |
| USDA FoodData Central | 245 g | 1.0355 g/mL | Published here |
The 227-gram pattern
The figure 227 is 8 × 28.35 — the conversion for weight ounces (avoirdupois). It is applied to volume in fluid ounces without going through the substance’s density. For a substance that happens to have a density of about 0.96 g/mL, the answer would be right; for water, milk, yogurt, cream, buttermilk, pumpkin purée, ricotta and evaporated milk, all of which are denser than water, it is wrong. The same number 227 appears on the King Arthur chart for every one of these ingredients, which is the signature of an arithmetic pattern rather than a measurement.
The full list of 227-gram rejections is on the corrections page.
The published figure and its sources
The full sourcing for buttermilk, including every accepted and rejected figure, the state or filling method behind each, and the physics or standards reasoning applied, is on the ingredient page.
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