Reasons Why Your Unopened Bottle of E-juice Turned Dark

Most freshly mixed e-juice flavors are clear and light in color. Image via E-liquid Recipes forum.

An e-juice flavor that doesn't have tobacco, chocolate, coffee or any dark ingredient is usually clear when you first bought it in an air-tight container with a childproof cap. Yet, after a few days of storage you noticed the liquid is slowly turning dark. What could be the reason for this? According to experienced vapers and e-juice manufacturers, there's a lot of reasons why the liquid may appear darker than before.

Reason #1: Your e-juice is reacting to heat exposure in a chemical process known as the Maillard Reaction.

So, what exactly is a Maillard Reaction? Chemical and Engineering News had a lively discussion with Vincenzo Fogliano, a food chemist at the University of Naples, Federico II, about it:

"Maillard discovered the reaction, but Hodge understood it," Fogliano said. In fact, because citations of Hodge's paper far outnumber those of Maillard's, there has been some discussion of renaming it the Maillard-Hodge reaction, but that idea hasn't yet caught on.

According to Hodge's model, the Maillard reaction has three stages. First, the carbonyl group of a sugar reacts with an amino group on a protein or amino acid to produce water and an unstable glycosylamine. Then, the glycosylamine undergoes Amadori rearrangements to produce a series of aminoketose compounds. Last, a multitude of molecules, including some with flavor, aroma, and color, are created when the aminoketose compounds undergo a host of further rearrangements, conversions, additions, and polymerizations.

This means that e-juice exposed to heat is likely to turn dark faster than those that were immediately refrigerated after they were manufactured. There's no specific temperature or range of degrees in either Fahrenheit or Celsius that were provided pertaining to a Maillard reaction happening with e-juice bottles exposed to room temperature or rising heat, or even direct sunlight.

Reason #2: Steeping, which involves the Maillard Reaction, can also cause your e-juice to darken in color.

The nicotine, carrier solvents, and flavoring agents in your e-juice are reacting to each other. In the cooking blog called Khymos, the Maillard reaction is further explained as a chemical process that happens even when the sugars and proteins in the liquid aren't exposed to heat.

One can speed up the [Maillard] reaction by adding protein or a reducing sugar, increasing the temperature, using less water (or boiling off water), and increasing the pH.

Even though sucrose is not a reducing sugar, it easily breaks up into fructose and glucose when heated, and these take part in the Maillard reaction. When a sugar is applied to a surface that is exposed to heat, there will be a fine line between caramelization, which involves only sugars, and the formation of Maillard products. If the surface contains proteins or amino acids, both caramelization and Maillard products will be observed.

A typical temperature range of 230 to 340°F (110–170°C) is often cited as ideal for the Maillard reaction to proceed in the normal time frame.

Contrary to popular belief, the Maillard reaction will also occur at lower temperatures. In vintage Champagne, autolyzed (inactive) yeast and sugars react to form Maillard products that yield a characteristic flavor profile. This reaction takes place in the cool chalk cellars of the Champagne district in France, where the temperature remains constant at 48 to 54°F (9–12°C) year round. Because of the low temperature, a much longer reaction time is needed, so the characteristic Maillard-influenced flavor is found only in aged Champagnes. If the temperature is increased, the reaction will proceed more quickly.

Reason #3: It's the result of a common chemical reaction known as oxidation.

Vape Ranks explains that nicotine is a major reason why e-liquids darken over time even when they're stored in unopened bottles.

Nicotine is a very reactive substance, and can cause e-liquid to change color either in reaction with other ingredients in the juice, or after being exposed to air, light or heat. Nicotine-containing juices tend to become darker over time, even when stored in cool, dark places, but some companies add small amounts of preservatives or stabilizers to prevent oxidation.

Reason #4: Your coil is full of gunk and it's seeping into the clearomizer's tank full of fresh e-juice.

Sometimes, you can't avoid leaving gunk all over your coils. The sugars in flavoring tend to caramelize when exposed to intense heat. Changing your e-juice flavors can increase the chances of seeing gunk coat the coils.

This "gunk", as it's commonly known in vaping circles, stains the e-liquid, an effect that becomes increasingly visible as the level of juice in the tank decreases. In extreme cases, 100% VG-based juices can start off as clear, amber-colored concoctions and become dark-brown goo by the time you reach the end of the tank. Simply adding fresh e-liquid will only cause it to darken even faster due to the gunk buildup on the coil, and the residue left in the tank.

What to Do When Your E-Juice Turns Brown or You Have Gunk on Your Coils

Make it a habit to clean your coils whenever you noticed residue forming around the wires. Here's one way of cleaning your coils:

Read Slim Vape Pen's blog on "Cleaning Your Atomizer Tank" with alcohol.

Never mix old juice with new. If you saw your old e-juice turn brown and it smelled funny, then throw it away, clean the tank and refill it with a fresh batch of e-liquid. This is what ECF veteran member AlterUrEgo advised:

What's happening is you have a cocoon of gunk around the coil. Your first heating up the cocoon trying to vaporize the liquid thus heating up the surrounding area caramelizing and darkening the juice. Replace the coil but don't add new juice to the old juice cause the old yuk juice will contaminate the new super quick, taste crappy and go dark. Throw the old juice away and start fresh.

Lastly, you should also change the wick, and if you have time, replace the coils with new ones. Use high-quality combined fiber for the wick and learn to build coils that fit your atomizer's specifications.