Blackberries are a type of fruit that contains seeds. Botanically, they are classified as an aggregate fruit, composed of many smaller, individual fruit units clustered together. Each tiny unit develops from a separate ovary within a single flower and holds a single seed inside its hard shell. This structural arrangement makes the seeds noticeable when consuming the fruit.
Blackberry Structure: Seeds and Drupelets
The structure perceived as a single blackberry is actually a cluster of small, independent spheres called drupelets. A mature blackberry can contain 50 to 100 or more of these miniature fruit segments tightly packed around a central core. Each drupelet is a small, complete fruit that contributes to the berry’s bumpy texture and juicy volume.
Within each drupelet is a hard, protective casing that houses the true seed. Botanically, this hard structure—the ovary wall fused with the seed—is often referred to as an achene. The achene protects the embryonic plant inside until conditions are right for germination.
The noticeable crunch when eating blackberries comes directly from the thick, lignified shell of the achene surrounding the seed. This shell is composed primarily of cellulose and lignin, making it highly resistant to digestion. The hard achenes remain intact while the fleshy parts of the drupelet dissolve, contributing a gritty sensation.
The formation process starts with the flower’s multiple pistils, each developing into one drupelet after successful pollination. As the fruit ripens, the outer layer of the drupelet becomes succulent, while the inner layer hardens around the developing seed. This simultaneous development of soft pulp and hard shell is characteristic of the aggregate fruit structure.
Practical Concerns: Eating and Preparation
The small, hard seeds found within blackberries are safe for consumption and generally pass through the digestive system without complication. While they pose no health risk, their presence can detract from the smooth texture desired in certain culinary applications. Nutritionally, the seeds contain beneficial omega-3 and omega-6 fatty acids, along with dietary fiber.
Cooks focus on seed removal primarily to create clear, smooth preparations like jellies, purees, and sauces. In jams, the seeds often settle to the bottom during setting, affecting the final appearance and consistency. Retaining the seeds is acceptable for rustic preparations or when using the berries for baking.
To achieve a smooth, seedless product, mechanical separation methods are employed after the berries have been gently cooked. Passing the softened pulp through a fine-mesh sieve or cheesecloth effectively traps the hard achenes, allowing the smooth liquid to pass through. Specialized tools like a food mill or a high-speed juicer offer a more efficient method for processing large batches.
Removing the seeds slightly reduces the overall volume of the finished product, as the achenes contribute a small percentage of the berry’s total mass. This process concentrates the flavor and natural pectin found in the pulp, resulting in a more intense taste and a better set for preserves.