Oxalates (oxalic acid) are naturally occurring compounds found in many plants, acting as a byproduct of their metabolism. These organic molecules bind to minerals like calcium within the plant structure. When consumed, oxalates interact with calcium in the body. Coffee does contain oxalates, but the precise quantity depends on context and preparation. This analysis details the measurable amount of oxalates in coffee, how that level is influenced by brewing methods, and how it compares to other common foods.
Oxalate Content in Brewed Coffee
The typical oxalate content in a standard eight-ounce (237 ml) cup of plain, black brewed coffee is low. Scientific analyses consistently place the range for unflavored coffee between 0.7 and 2.4 milligrams of oxalate per serving. This places coffee in the category of a low-oxalate beverage compared against many other plant-derived foods.
The amount that affects the body is primarily the soluble oxalate fraction. Plants contain both soluble oxalates, which dissolve easily in water and are readily absorbed, and insoluble oxalates, which are bound to minerals. Since coffee is an infusion, the final brew contains only the soluble compounds extracted from the bean.
The low concentration is a significant factor in evaluating coffee’s impact on dietary intake. Roasting and brewing typically do not extract a large percentage of the total oxalate content present in the raw bean. Consequently, daily consumption of black coffee contributes only a minor amount to a person’s total oxalate consumption.
Variables That Change Oxalate Levels
The amount of oxalate extracted into the cup depends on several factors related to the coffee bean and the preparation method. One influential factor is the length of time the coffee grounds are in contact with water, known as the brewing time. Oxalate content increases proportionally as the brewing time is extended, due to the continuous extraction of soluble compounds.
The degree of coffee grinding also plays a role in the final concentration. A finer grind increases the total surface area exposed to the water, facilitating a higher rate of extraction for the oxalate compounds. Using a medium grind, as opposed to a fine one, can slow the penetration of soluble oxalates into the brew.
The type of coffee bean also presents variation in the natural oxalate load. Studies show that Coffea arabica beans tend to have lower oxalates than Coffea robusta beans. While the direct quantitative effect on oxalates is not always clear, high heat exposure during darker roasting may slightly reduce the concentration of various organic compounds.
Comparing Coffee to Other Dietary Sources
Understanding coffee’s oxalate load requires comparing its small quantity to foods known for high concentrations. A single eight-ounce cup of coffee, containing less than 3 milligrams of oxalate, contributes very little to the average daily intake. This is apparent when looking at high-oxalate items.
For instance, a half-cup serving of cooked spinach can contain over 750 milligrams of oxalate. A one-ounce serving of almonds typically contains approximately 122 milligrams of oxalate. Even beverages like black tea are significantly higher, often ranging from 50 to over 100 milligrams per serving depending on brewing strength and time.
Chocolate is another food that dwarfs coffee’s oxalate content; a single cup of hot chocolate can easily exceed 65 milligrams. People monitor oxalate intake because these compounds can bind with calcium to form crystals, which may contribute to kidney stone formation. The low concentration in coffee means it is not considered a significant contributor to the dietary oxalate burden, unlike many other common plant-based foods and drinks.