Rhubarb is famous for its vibrant, ruby-red stems, though its tart, edible stalks are often used like a fruit in cooking. Many home cooks and gardeners question why some stalks appear green. This color variation is often mistakenly linked to the plant’s ripeness, safety, or overall quality. Understanding the source of the color difference is key to appreciating all varieties of this unique crop.
The Role of Genetics in Stalk Color
The most significant factor determining whether a rhubarb stalk is red or green is the plant’s genetic makeup, specifically the cultivar or variety. The red hue comes from pigments called anthocyanins, which are natural compounds also responsible for the color in blueberries and red cabbage. Varieties like ‘Valentine’ and ‘Canada Red’ are genetically predisposed to produce high levels of these pigments, resulting in deeply colored stalks.
However, many perfectly healthy and popular varieties, such as ‘Victoria’ or ‘Green Stalk,’ are simply bred to produce very little or no anthocyanin. These plants will be green regardless of how long they are left in the ground or how they are grown. The absence of this pigment is a stable genetic trait, not a flaw. Therefore, a bright green stalk is not an unripe stalk; it is simply a genetically green stalk.
Environmental Factors Affecting Pigmentation
While genetics sets the potential color range, external conditions can influence the final intensity of the red pigment in varieties capable of producing it. For instance, field-grown rhubarb exposed to excessive heat and sun can sometimes lose some of its deep color, resulting in a paler, greener tinge. The production of anthocyanin is sensitive to environmental stressors.
Paradoxically, the deep red stalks often seen in early spring or commercially are a result of “forcing” the rhubarb by growing it in darkness or very low light conditions. This technique yields tender, brightly colored stalks. Soil conditions also play a role, as rhubarb prefers a slightly acidic to neutral pH. Furthermore, high nitrogen levels in the soil can encourage leafy growth at the expense of stalk coloration, leading to a greener appearance even in red-hued cultivars.
Safety and Culinary Differences
A primary concern for many growers is whether a green stalk is safe to consume, and the answer is an unambiguous yes. The color of the stalk offers no indication of the concentration of oxalic acid, which is the compound that makes rhubarb leaves toxic. The critical safety distinction is between the stalk and the leaf.
Rhubarb leaves contain high levels of oxalic acid and should always be removed and discarded before cooking. The edible green stalks are just as safe as red ones and contain a negligible amount of the compound. The main difference between the colors is a slight variation in flavor profile. Green varieties are often described as having a more intensely tart flavor than their red counterparts, which may require slightly more sugar in recipes. The texture and cooking performance are essentially identical, and some green varieties are prized for their superior yield and less stringy texture.