Why is my resveratrol brown? Understanding color changes in your supplement

December 27, 2025 •

4 min read

Research indicates that trans-resveratrol, the active form of this popular antioxidant, is highly sensitive to light and oxidation, which can lead to its degradation and a noticeable color change. For this reason, knowing why is my resveratrol brown can reveal critical information about its quality and potency.

Quick Summary

Resveratrol's brown color can result from several factors, including the natural source material, such as Japanese knotweed root, or chemical degradation from exposure to light, heat, and air. This discoloration can indicate a loss of potency due to oxidation or isomerization, but its significance depends on the product's original formulation and storage conditions.

Key Points

Natural vs. Synthetic: Natural resveratrol extracts from sources like Japanese knotweed are normally brown, while high-purity synthetic powder is white or off-white.
Oxidation causes degradation: Resveratrol's antioxidant properties make it vulnerable to oxidation when exposed to air, light, and heat, causing it to turn brown and lose potency.
Photoisomerization reduces potency: UV light exposure can convert the more potent trans-resveratrol into the less active cis-resveratrol, which contributes to discoloration.
Poor storage accelerates decay: Storing resveratrol improperly in humid or warm environments can speed up the degradation process.
Brown color isn't always bad: A consistently brown color in a natural extract is normal, but a color change from white to brown indicates diminished effectiveness in a synthetic product.
Proper storage is key to potency: Keeping your resveratrol in a cool, dark, and dry place in a tightly sealed container can help preserve its stability and active properties.

Is brown resveratrol bad? Factors influencing color

There are several key reasons your resveratrol may appear brown, and not all of them indicate a bad or expired product. Understanding the source and the potential for degradation is crucial for interpreting the color change.

Natural vs. Synthetic Resveratrol

One of the most common reasons for a brownish tint is the supplement's origin. Resveratrol is available in two primary forms: a natural extract and a high-purity, synthetic powder.

Natural Extracts: Many resveratrol supplements are derived from plant sources, most notably Japanese knotweed (Polygonum cuspidatum). This root extract naturally contains various other compounds and pigments, which give the powder its characteristic brownish color. This is a normal and expected color for such a product and does not indicate a loss of efficacy. In fact, some prefer these whole-plant extracts for the potential synergistic effects of other phytochemicals.
High-Purity Synthetic Resveratrol: In contrast, high-purity (e.g., 98% or higher) synthetic resveratrol powder is typically white or off-white. If a product that was originally white or off-white turns brown, it is a definitive sign of degradation, as the high level of purity means there are no other plant materials to cause discoloration.

Oxidation and Isomerization

Resveratrol is an antioxidant, and its very nature makes it susceptible to degradation. As an antioxidant, it donates electrons to neutralize free radicals, and this process can cause it to oxidize. The oxidized molecules then undergo further chemical reactions that lead to a visible color change.

Exposure to Oxygen: Resveratrol is a polyphenol, and like many compounds in this class, it is sensitive to air. A bottle that is not sealed tightly, or a powder exposed to open air, will oxidize over time and turn brown.
Heat and Light: Resveratrol is notoriously unstable when exposed to heat and ultraviolet (UV) light. UV irradiation, in particular, causes the degradation of the beneficial trans-resveratrol isomer into the less active cis-resveratrol. This photoisomerization is a chemical change that can also cause discoloration.
Oxidizing Metals: Even trace amounts of oxidizing metals like iron or copper can act as catalysts to accelerate the discoloration and degradation process.

How to tell if your resveratrol has degraded

It can be difficult to know for certain if your resveratrol has lost potency without laboratory testing. However, some key indicators can help you assess your product's condition.

Check the original color: If you remember the powder or capsule content being a light off-white color and it has since darkened to a deep reddish-brown, it is highly likely that oxidation has occurred.
Examine the storage conditions: If you've been storing your supplement in a bathroom cabinet, on a kitchen countertop, or near a window where it's exposed to heat, humidity, or sunlight, degradation is very probable.
Consider the source: If your supplement is a whole-root extract and has always been brownish, the color is likely normal. It is the color change of a high-purity product that is cause for concern.

Comparison of resveratrol supplement types

To clarify the difference between product types, the following table summarizes the typical characteristics of natural extracts versus high-purity synthetic versions.


Feature	High-Purity Synthetic Resveratrol	Natural Japanese Knotweed Extract
Starting Color	White or off-white powder	Light to darker brown powder
Source	Laboratory synthesis	Extracted from Polygonum cuspidatum roots
Purity	Often 98% or higher trans-resveratrol	Lower percentage, typically 50%
Degradation Indicator	Turns visibly brown from initial light color	Color is consistently brownish; change is harder to detect
Stability	Very sensitive to light, heat, and oxygen	Contains other plant compounds which may offer some stability, but still susceptible to degradation

Proper storage to prevent degradation

To ensure your resveratrol remains as potent as possible, follow these best practices for storage:

Store in a cool, dark place: Keep your supplements away from heat sources and out of direct sunlight. A cabinet or pantry is a much better location than a kitchen counter or bathroom shelf.
Keep it dry: Humidity can also affect supplement stability. A cool, dry environment is ideal.
Seal tightly: Always ensure the lid is screwed on tightly after each use to minimize exposure to oxygen.
Consider refrigeration: Some manufacturers recommend refrigeration after opening, especially for liquid formulations, to maximize shelf life. If your container specifies this, be sure to follow the instructions. However, unless indicated, the fridge's humidity can also be detrimental.
Note the expiration date: Always check the expiration date and use the product within the recommended timeframe. Although a color change may not always signify total degradation, it can be a warning sign as the product nears its shelf life.

Conclusion

Seeing a brown color in your resveratrol supplement is not an automatic cause for concern, but it does warrant investigation. If your product is a natural extract, a brownish color is likely normal. However, if you purchased a high-purity, white or off-white supplement and it has since turned brown, it has likely degraded due to oxidation or isomerization, resulting in a loss of potency. By understanding the causes of discoloration and implementing proper storage techniques, you can ensure your antioxidant supplement remains fresh and effective. Always review the product label and manufacturer recommendations to understand your specific supplement's characteristics.

For more detailed scientific information on resveratrol's properties and stability, consult authoritative sources like the National Institutes of Health (NIH) library. PMC. Resveratrol—A Promising Therapeutic Agent with Problematic Properties

Frequently Asked Questions

Not necessarily. If the product is a natural extract from sources like Japanese knotweed, it is naturally brown. However, if a high-purity, synthetic product that was originally white has turned brown, it indicates that it has likely oxidized and lost some potency, especially if it is past its expiration date.

Resveratrol can change color due to oxidation, a chemical process that occurs from exposure to oxygen, heat, and light. UV light exposure, in particular, can also cause isomerization, converting the stable trans-resveratrol into the unstable cis-form, leading to further discoloration.

To prevent browning and maintain potency, store resveratrol supplements in a cool, dark, and dry location. Keep the container tightly sealed to minimize oxygen exposure and avoid places with high heat or humidity, like bathrooms or kitchen counters.

While consuming discolored resveratrol is not typically toxic, especially if it is a natural extract, it may have a reduced potency and may not provide the full benefits. If a high-purity supplement has visibly degraded, the active compounds may have broken down significantly.

Yes, by minimizing its exposure to heat, light, and air. Storing it in its original opaque, sealed container in a cool, dry place is the most effective way to slow down the oxidation process and preserve its quality.

If your new bottle contains a natural extract, for example from Japanese knotweed, a brownish color is completely normal due to other plant compounds present in the material. It is not a sign of a defective product in this case.

Yes, potentially. Assuming identical source material, a white powder turning brown over time indicates oxidation and a loss of the bioactive trans-resveratrol. A product that is brown from the start due to its natural extract may still have high potency, but a high-purity product that has changed color is no longer at peak efficacy.