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Why are blackberries purple?

Blackberries come in a range of colors, from bright red to deep purple. But why are some blackberries such a vivid purple hue? The pigments that give blackberries their color provide clues into their ripening process and nutritional value. Join me as we explore the science behind blackberry colors.

The Role of Anthocyanins

The purple, blue, and red colors found in blackberries are caused by anthocyanin pigments. Anthocyanins are antioxidant compounds in the flavonoid family. They are found in high concentrations in deeply colored fruits and vegetables.

Anthocyanins serve multiple purposes in plants:

  • Attract pollinators and seed dispersers
  • Protect plants from stressors like sunlight, cold, and injury
  • Scavenge free radicals

In blackberries, anthocyanin concentration increases as the fruit ripens. Green berries transition to red, then ultimately turn deep purple-black when fully ripe. The most abundant anthocyanins found in blackberries are cyanidin-3-glucoside and cyanidin-3-rutinoside.

Anthocyanin Production

Anthocyanin pigments are synthesized from simple organic compounds in cell vacuoles. Their production is influenced by:

  • pH
  • Sugars
  • Light
  • Temperature
  • Plant hormones

Acidic vacuolar pH favors anthocyanin formation. The optimal pH for anthocyanin stability is around 3.0-3.5. Sugars also drive anthocyanin synthesis, both as precursors and signaling molecules. Exposure to light, specifically blue and UV light, boosts production.

Cool night temperatures help anthocyanins accumulate. Warm days and cold nights create ideal conditions for blackberries to turn deep purple. Stress hormones like abscisic acid augment anthocyanin levels when plants experience drought, injury, or nutrient deficiency. All these factors interact to generate rich pigmentation in ripe blackberries.

Anthocyanin Variations

Not all blackberries turn the same shade of purple. Evergreen blackberries remain red when ripe. Other varieties develop purple pigmentation in a mottled, patchy pattern. What accounts for this anthocyanin variation?

The genotype or cultivar determines a blackberry’s base anthocyanin potential. But environmental factors also influence color expression. For example:

  • Shade reduces anthocyanins
  • Overwatering dilutes anthocyanins
  • Hot temperatures degrade anthocyanins
  • Poor soil nutrition limits anthocyanins

Managing these environmental stresses is key to maximizing anthocyanin production and achieving deep purple blackberry hues.

Anthocyanin Degradation

Once blackberries are harvested, anthocyanins remain relatively stable but begin slowly degrading. The vibrant purple color eventually fades to reddish-purple, then brownish-red. Three factors contribute to anthocyanin breakdown after picking:

  • Temperature: Heat accelerates degradation reactions.
  • Oxygen: Anthocyanins oxidize in the presence of oxygen.
  • pH: Values above 4.0 destabilize anthocyanins.

To slow anthocyanin degradation and retain maximum purple color, freshly harvested blackberries should be immediately refrigerated. Storing berries below 40°F inhibits enzymatic activity and oxidation reactions. Acidifying the storage environment with a little lemon juice also helps stabilize anthocyanins.

Health Benefits of Anthocyanins

The anthocyanins that give blackberries their signature hue provide tangible health benefits. As potent antioxidants, they:

  • Protect cells from free radical damage
  • Reduce inflammation
  • Boost immunity
  • Support heart health
  • Improve cognition
  • Fight cancer

Here is a table summarizing some of the key research on anthocyanin health benefits:

Study Key Findings
12 adults drank blackberry juice daily for 1 week (Kuntz et al. 2015) – 8% increase in antioxidant capacity of blood plasma
Mice fed blackberry extract for 10 weeks (Blando et al. 2004) – Less blood platelet aggregation
– Less arterial plaque formation
Human intestinal cells treated with blackberry extract (Brown et al. 2012) – Reduced inflammation markers IL-8 and NF-kB
Rats fed blackberry diet for 8 weeks (Rosenblat et al. 2015) – Improved memory and cognition

By scavenging free radicals and combating inflammation, blackberry anthocyanins promote whole body health, from gut to brain.

Factors Influencing Anthocyanin Bioavailability

To receive the benefits of blackberry anthocyanins, they must be absorbed from the digestive tract into circulation. Unfortunately, factors like pH, digestive enzymes, and microbiota can degrade anthocyanins and limit their bioavailability. Here are three main factors influencing anthocyanin bioavailability:

  • pH: Anthocyanins degrade at neutral pH in intestines.
  • Microbiota: Intestinal bacteria metabolize anthocyanins.
  • Cellular Uptake: Anthocyanin transport into cells is inefficient.

Strategies like combining blackberries with probiotics, vitamin C, or milk proteins may help stabilize anthocyanins and enhance absorption. But more human trials are needed on improving the bioavailability of dietary anthocyanins.

Harvesting Blackberries by Color

When harvesting blackberries for eating fresh or cooking, use color as your ripeness indicator:

  • Green berries – underripe, sour, low sugar
  • Red berries – ripening, moderately sweet
  • Dark purple berries – fully ripe, sweetest flavor

Choose deep purple-black berries for immediate use. If you won’t be using them right away:

  • Harvest when red if storing several days
  • Harvest when green-red if freezing or preserving

Just be sure to handle ripe berries gently to avoid smashing their delicate druplets.

Maximizing Blackberry Anthocyanins

Follow these tips for getting the most anthocyanins from blackberries:

  • Choose fully ripe, dark purple berries
  • Refrigerate promptly after harvesting
  • Avoid washing until ready to eat
  • Consume berries raw or with minimal cooking
  • Pair with probiotics or vitamin C foods
  • Freeze extra berries while fresh

Freezing is ideal for long-term storage, as it deactivates anthocyanin-degrading enzymes. Thawing and consuming the juice helps preserve benefits.


The eye-catching purple hue of blackberries originates from anthocyanin pigments. These beneficial polyphenols accumulate as the berries ripen, transforming bitter green fruit into sweet, dark-colored delights. Anthocyanins also equip blackberries with antioxidant, anti-inflammatory, and anti-cancer powers. Understanding the chemistry behind blackberry color unlocks the key to experiencing these nutritious berries at their most flavorful and wholesome.