Diacetyl, Diketones and Custard Notes

flavours that contain custard notes
TFA Custard

Let’s take a look at Diketones and my opinions, the anti-vape rhetoric and scare tactics, and offer up a spread of common-sense, shall we? Diketones and Custard Notes are a hot topic within the vaping world, especially as they pertain to what we’re inhaling, and what if any, are the levels of harm from long-term use. 

But just how much of a risk these ingredients pose is the question at hand. Moreover, considering that vaping is harm reduction, and at times a short-term cessation method, are we being overly cautious?

What is Diacetyl? What are Diketones and Custard Notes?

Diacetyl (DA) and Acetyl Propionyl (AP) fall under the classification or class of Diketones. They are molecules responsible for the rich buttery aroma and flavour that is widely used in the food and beverage industries. 

Custard notes is a broader term used to classify similar molecule types, and also represent flavours with a custard, vanilla and or buttery note. They include the two mentioned above, Diacetyl and Acetyl Propionyl, and also Acetoin and Butyric Acid, AKA Butanoic Acid.

Any of these custard notes may be used in the manufacturing of certain concentrated flavours and e-liquids. Although many classify Acetoin as a diketone, it is in fact a Chiral molecule not a diketone. I too have made this mistake.

Diacetyl is the most controversial of all custard notes and the one that generates the most debate and concern. It also exists in nature and is a by-product of fermentation. It is present in a wide variety of desserts, breads, coffee, alcohols, certain fruits, and dairy products such as cheese, milk, and creams. It’s also common in lollies or candy.

Due to its presence naturally, many concentrated flavours and e-liquids will have at least small traces of diketones and or custard notes. As an example, It’s virtually impossible to produce an authentic tasting vanilla custard without the molecule that provides such a flavour. 

(Links for additional information on these custard notes at the bottom of this post)

It’s one of nature’s natural flavour enhancers, and it’s served up with an extra dollop of yumminess.

The FDA classifies these molecules as GRASS, or generally regarded as safe for regular consumption. But it is vaping, and thus inhalation that may or may not be problematic, and it is partly this speculation and uncertainty that continues to fuel ongoing discussion and debate.

Where did this concern stem from, and what are the possible risks?

Vapers became aware of diacetyl being used in e-liquids as far back as late 2009. However, an older case involving factory workers in a U.S. microwave popcorn plant, brought further attention to diacetyl and the possible risks from inhalation.

Eight of the workers contracted Bronchiolitis Obliterans, also known as ‘Popcorn Lung’, which is a severe, irreversible condition that scars the lung sacs. It was thought, though never proven, that powdered Diacetyl was the cause.

Regardless of this, many opposed to vaping used this case as ammunition, in an attempt to both demonise and steer smokers away from a viable cessation method.  I need not point out that there is a huge difference between “powdered” diacetyl, and traces of diacetyl in an aerosol. Oh, I just did. 

COPD and Emphysema 

Smoking has long been associated with these conditions, however, much is still not known as to its cause. Concerns regarding the potential harm from diketones when smoking were brought up by Dr Farsalinos at the Global Forum on Nicotine. He said that it is likely that Diacetyl, Acetyl Propionyl or both, at least to some degree, are contributory factors to COPD and Emphysema.

Whilst this could lead one to assume that the risk to vapers may also be present, more research and testing is needed before any absolutes are reached. Dr Farsalinos is of the opinion that diketones, both DA and AP, should not be added to e-liquids.

Diketones in Cigarettes vs. e-liquids – The common-sense part

Dr Michael Siegel, a professor at Boston University School of Public Health (an advocate for harm reduction) has gone on record stating that “daily exposure to diacetyl from smoking is 750 times higher than exposure to diacetyl from vaping”.

Therefore, can one conclude that the chance of vapers contracting a serious lung condition due to custard notes, would at the very least be unlikely, especially for short-term use? Whilst I feel this has merit, it is based on having limited medical or scientific knowledge. Personally, I do limit my intake of e-liquids with custard notes, particularly diacetyl. 

Below is a chart representing average findings.

Reducing Diacetyl and Custard Notes

A few years ago, many of the more reputable flavouring companies began eliminating additional custard notes from their formulas, particularly those with the greatest potential for long-term harm.  A number of e-liquid manufacturers followed suit, particularly after the whole Five Pawns incident.

As such, many manufacturers are using safer alternatives to Diacetyl and Acetyl Propionyl; namely Acetoin and Butyric Acid. Perhaps sooner than later, both DA and AP will unlikely be an addition to any reputable brands. Acetoin, although known to be substantially safer, is another note that some are removing. I feel that the use of Butyric Acid, considered the safest alternative, will no doubt become more common place.

An example of these flavouring offerings is Capella’s version 2 line, which is free of Diacetyl, Acetyl Propionyl and Acetoin. Also, TPA-TFA’s DX line of Diacetyl-Diketone and Acetoin free flavours.

Flavour Concentrates - Safety Data Sheets

Apart from TFA and Capella’s offerings, both FlavourArt and Flavorah are transparent about their ingredients, and both rarely add additional diacetyl, and the few containing diketones or custard notes, are listed on their sites.

See our post-database providing details and links on flavouring companies and their ingredients –
Flavour Manufacturers Safety Data Sheets Database

So, should we or should we not?

It is not my intention to dispel scientific findings or recommendations by those qualified to offer them. However, I feel in contrast to smoking, vaping flavours with diketones is still a significantly less harmful alternative.

Today, more and more of these concentrates are being offered with safer alternatives, such as Butyric Acid; some are even devoid of additional custard notes. For peace of mind, and just to be on the safe side, if the option is there to purchase these lower risk alternatives, one may wish to try them.

References and Research: 

Charles Yates

AKA Charles Vaper. Ex-smoker, current vaper and THR advocate. I started The Vapers Table in 2011 to offer information and support for smokers looking to transition to vaping. My interests are- Helping smokers quit, food, cooking, flavours, music, orchestral composing-studio recording & technology, travel & country road trips.