“What do you think of this?” As I arrive for my shift behind the bar my colleague hands me a small pour of a hazy, pale amber beer. His face is expressionless. Is this a test of some kind? I take a couple of sniffs of the beer and say, “It smells like vanilla? Like cream soda?” I take a sip of it. “Urgh. It’s so sweet. What is it? It tastes like artificial sweetener. It’s gross. What is it?” I hand it back. He names the beer. I recognise the name, it’s an IPA from a British brewery. I’m not 100% sure I’ve tried this specific beer before but I know no IPA should smell or taste like that.
The following week I taste a DIPA and immediately an epic battle commences in my mouth between BITTERNESS and OVERWHELMING SWEETNESS (not just sweet but sickly too, like artificial sweetener). It’s unpleasant to the point of being unenjoyable. Later on I ask some friends what they think of the same beer. One confidently says, ‘yeah, that's got diacetyl'; the other agrees, adding ‘it’s so buttery’.
After this particular exchange I am approaching the end of my personal Journey of Realisation - that I’m not immune to diacetyl after all. I just perceive it differently to pretty much every other person I’ve ever discussed it with over the years.
While I'm getting my head round the idea that my vanilla = everyone else’s butter a couple of previous episodes of ‘funny tasting beer’ come drifting back, where pale ales and IPAs tasted of vanilla to me but not to anyone else. I even know someone who won a medal for a homebrewed saison that tasted like cream soda to me. I knew it didn’t taste right at the time but I couldn’t have said what the specific fault was then (other than saisons shouldn’t taste of cream soda, obviously). But I could now.
Until this day nobody had EVER mentioned vanilla to me in relation to diacetyl. I had even asked a couple of brewers, specifically what could give rise to vanilla as an ‘off flavour’ and nobody knew. When I tweeted about my recent experience someone tried to tell me it was a commonly used descriptor for diacetyl, but I have never seen it before. Once I got home I started going through the brewing library. Luckily Dr George Fix came to the rescue (1). While discussing the preference some people have for beers with prevalent diacetyl he notes that:
“The vanilla tone, which is often confused with caramel flavoring, definitely adds to the smoothness of beer.”
Ah, so it's not just me then. Well, that's a relief.
At this point I should mention that before I switched to a career in biomedicine I used to work in a QC/chemical analysis lab at Yoplait Dairy Crest where I was known as a bit of a vanilla super taster - I am very sensitive to low levels of vanilla. Part of my role was tasting products to check they matched their specification, to detect if there was too much or too little flavouring in the final product. If you were lazy you could cheat and judge visually for flavours like strawberry or cherry but because vanilla yogurt is white you can't tell by looking - you can only tell by taste.
But even before I had my professional experience with vanilla, I had already come to love it as a child who did a serious amount of baking. In fact, for most of my early teens I thought I was going to become a professional baker of some kind when I left school. I actually used 'cake mix' as a beer flavour descriptor recently because to me it's shorthand for 'smells like a rich, sweet perfumy batter'. Perhaps in future I’ll just learn to say ‘urgh, diacetyl’ instead.
So, yes, I love vanilla but the flavour completely spoils pale ales and IPAs for me.
So what is diacetyl? As mentioned above it is generally recognised as an off flavour in beer, although it is acceptable in certain styles, e.g English bitters, Scotch ales or Czech pilsners. The standard description for the flavour is ‘buttery’, but you will also find ‘butterscotch, caramel, creamy, milky’ mentioned. Diacetyl can also be experienced as a mouthfeel sensation - it can be perceived as ‘slippery’ or ‘slick’.
The commercial use for diacetyl is literally making things taste like butter. Anything which is meant to taste like butter, from margarine to Butterkist, will be flavoured with diacetyl.
Diacetyl is a natural byproduct of fermentation. You cannot eliminate it so the key is to control its presence in beer styles where it should not be evident. Fortunately, yeast is capable (depending on strain) of reabsorbing diacetyl and converting it into more palatable compounds. The simplest way for brewers to avoid diacetyl in their finished beer is to start fermentation with a sufficient amount of healthy yeast and provide the right conditions for the yeast to do its work. Once fermentation is almost complete, raising the temperature will allow the yeast to ‘clean up’ the finished beer. This process is called a ‘diacetyl rest’ and is especially important for lagers.
However, diacetyl it is also produced by species of lactic acid bacteria, Pediococcus and Lactobacillus. So unintentional diacetyl in a finished beer may indicate a contamination issue in the brewery, or in lines/taps at the point of dispense. This contributes to the negative reputation of diacetyl.
So what is wrong with my palate?
Short answer: I haven’t found out yet. I’ve participated in many off flavour tasting sessions, from both sides of the table, and (until now) diacetyl has remained the one major off flavour that I have struggled with. I’ve never been 100% confident that I can detect it in the kinds of beers I like to drink, although I seem to 'get it' alright when using the off flavour kits. When discussing the fault in commercial beers other people have always said they get ‘butter, caramel, butterscotch, popcorn’ and I just go, ‘um...I don’t know...is it really sweet?’ When your answer is different to everyone else’s you tend to think that you’re wrong and you just don’t get it. But perhaps that isn’t always the case.
I began to wonder how vanilla and butter could be confused as the same flavour. One is sweet, the other is fatty. One is worn as a fragrance, the other is exclusively a foodstuff. I still can't make sense of it.
As a vanilla lover I have previously explored the differences between vanilla extract (which contains natural flavour from vanilla beans extracted into ethanol) and vanilla essence (which is usually synthetic vanillin). Natural vanilla flavour is comprised of hundreds of components of which vanillin is the most prominent. If anyone wants to get into the science of artificial vs natural flavourings (both vanilla and butter) in a bit more depth then I highly recommend the Kennedy article, linked below (2).
Vanilla has a striking aroma which can be overwhelming when overdone but at lower levels is warm and comforting, maybe even romantic. Do you find a Victoria sponge cake to have a striking vanilla character? Possibly not but it’s definitely in there somewhere and it’s an integral part of its overall cakeyness. In fact, most so-called ‘plain’ or ‘white’ sponge cakes and cupcakes contain vanilla flavouring because it's used as a flavour enhancer - it gives us that impression of naughty sweetness which we desire and expect.
Answers on a postcard
The purpose of this post was to share my strange experience of finally 'getting' an off flavour after all these years. I have held back the scientific detail on diacetyl and vanilla as none of it really explains why I get vanilla or artificial sweetener instead of butter (but I'll definitely keep looking for the answer to that).
I'm keen to hear from anyone else who has had a similar experience of getting a completely different impression of an off flavour to the one which is cited by almost everyone else they have ever mentioned it to. I feel as if I must have a loose connection somewhere.
1.Principles of Brewing Science (Second ed.) George Fix. (1999)