Identifying faults, off flavours and other issues

Making cider and perry can sound like a simple task, you press the juice, you seal it in a container and a few weeks later — voila — yeast has converted the sugar to alcohol. Reality is that it’s quite a bit more complex and there are many saboteurs that want to ruin it for you. Some are more common and obvious than others, but for a new maker or even experienced drinker, knowing about and understanding the effects of these saboteurs can be useful knowledge. It’s a subject rarely covered and we’re not sure why, but hopefully the introduction and somewhat rough guide below will be useful.

What this page is meant to do is provide an unbiased guide on recognised faults in cider and perry production and flavours that aren’t generally considered “common” in certain ciders. It is not an attempt to identify or criticise certain products or producers. There are a couple of styles that have perceptible amounts of certain faults which will be explained, but for producers who intentionally introduce off-flavours or faults then the onus is on them to be transparent about it to ensure consumers can make informed choices. 

Before we start getting in to the different off-flavours and faults, a little trip back to basics might help with what process to follow to identify them.

There are three stages to tasting a cider which we follow here in our reviews: colour, smell and taste. 

  1. The colour is the first step and can give a really good initial indication of what to expect. For example a cider made from eating apples, say Braeburn or Cox will naturally be pale in colour. If it pours a dark amber colour then you know that either it has something added to it (say co-fermented with Raspberries) or it’s perhaps spent time in a barrel, or if neither of those things then perhaps it has oxidised, in which case you will expect to taste acetic acid or stale, cardboardy, sherried notes. 
  1. The smell can offer your next clue, as many of the off-flavours and faults listed below are volatile, meaning that they can give off an aroma. Sticking with acetic acid, most of us know what vinegar smells like and when present in cider the smell is similar.
  1. The taste. There are some faults that aren’t detectable in the colour or aroma, so taste is the only way you will find them. There is also the odd one that not everybody can taste, but we’ll come to that shortly. 

Anyway, let’s begin with the most common of all:

Acetic Acid

The basic process of making cider is yeast converting sugar to alcohol, which needs to be done anaerobically (without Oxygen present). If Oxygen is allowed to enter then a bacterial process can occur where acetobacter convert alcohol into acetic acid. If you’d like to know a lot more, then check out Adam’s piece here. It’s a controversial element as in small amounts it can add to the character of a cider and many people like its presence.

What does it look like: this is an oxidation process, so just as an apple will turn brown when cut open and left, so too can the cider. That’s not to say all dark ciders will be acetic, many tannic varieties such as Yarlington Mill can produce a very rich tan colour. However if it’s an Egremont Russet cider for example then a very dark colour possibly suggests it’s oxidised. See the photos below of the same cider, one bottled with a rather large air gap and the other not, you can see how over a couple of weeks the oxidation process has changed the colour.

How does it smell: very volatile and in brief, like vinegar. Although it’s never quite as clear as that as it can blend into the other aromas of the cider depending on how much is present. Can also be inhibited on the nose in very sweet ciders.

How does it taste: in small amounts it can add a twang, in larger quantities it will start to create a burn at the back of your throat. In those larger quantities the well known vinegar flavour will be fairly obvious.

Ethyl Acetate

A natural chemical compound produced during fermentation by wild non-saccharomyces (non-sugar) yeast. In low levels it can contribute to flavour balance, but in high amounts creates a solvent like character. Very sensitive to Sulphite addition.

What does it look like: not a visible fault.

How does it smell: like nail varnish remover or acetone.

How does it taste:  as above, not that we’ve drunk nail polish remover. A strong chemical, almost metallic taint to the flavour.

Sulphides (not to be confused with Sulphite)

The production of hydrogen sulphide and/or sulphur dioxide, is probably the second most common fault and often a result of stressed yeast. Can occur during primary fermentation or during bottle conditioning, particularly if the yeast has insufficient nutrients to carry out the fermentation. Much harder to get rid of during primary fermentation. If given time it can eventually clear, but it can be a long wait.

What does it look like: again not a visible fault.

How does it smell: sulphurous or rotten eggs, very volatile so can dissipate quickly but also perceived in very small quantities.

How does it taste: see ‘how does it smell’. Though it’s so volatile, it can often have dissipated before you taste depending on how much is present. So one that’s more on the nose than in the mouth.


Caused by a spoilage bacteria and very common in ciders or perries with high pH. Around 40% of drinkers are genetically unable to detect its presence.

What does it look like: not visible

How does it smell: Not a volatile fault usually, but in high concentrations you can smell it (or at least James thinks he can). Like a mouse cage, old damp newspapers and stale digestive biscuits.

How does it taste: if you’re unfortunate to be able to taste it, then it’s very similar to the smell. Sometimes confused with biscuity notes of lees ageing, but in practice tastes nothing like it.  Leaves a stale savoury note at the back of your throat.


More common in cider made from dessert or culinary apples as it tends to occur in fast and warm fermentations, which you often get in the warmer months at the end of summer, before cider apple varieties are ripe.

What does it look like: not a visible fault.

How does it smell: like fresh paint

How does it taste: chemical and solvent like taste.

TCA –  Trichloroanisole

Not something we come across often on Cider Review other than very occasionally. Also known as “corked” in wine, but not exclusive to alcohol under cork as this compound can be found in wood and paper based materials too. So storage conditions and materials play a key part in the development of this as it can take some time and higher temperatures and air to develop. Formed in the presence of Chlorine too, so cleaning materials (including water) can influence its production.

What does it look like: not visible

How does it smell: cardboard boxes left out in the rain, mouldy newspapers and damp basements.

How does it taste: musty cardboard, wet dog or mouldy basements, thin and paper like, generally stale. As though some of the flavour has been sucked out leaving a blank sheet [Ed: of paper…sorry I had to].


In some ways not considered a fault as it is actually a strain of yeast, used on purpose in some drinks, but in wine and cider can be considered a fault depending on the strain, its concentration, the style of wine or cider it infects and the culture in which it is found. It tends to be scrupulously avoided by Spanish producers, for instance, whereas in France, traditional production methods meant it was historically a far-more-frequent occurrence. For more details on the thorny nature of brettanomyces — ‘brett’ — across cider and other drinks categories, see our article here.

What does it look like: not always a visual effect, but in aerobic conditions starts to produce acetic acid (see above)

How does it smell: Dependent on strain and concentration, anything from savoury spices to meatiness, old barns, and sweaty leather.

How does it taste: ranges from spicy, savoury tones to leather, animal character (‘sweaty horse’ is a common descriptor’) and strong medical notes in higher concentrations.

Explosive Nucleation

No we’re not talking about volcanoes, although the process is similar. Nucleation is the process by which dissolved Carbon Dioxide bubbles collect on a defect in a glass or bottle and once they combine and grow are released into the drink to rise to the surface. Most glasses have a deliberate widget in the bottom to get those bubbles forming and rising. However on occasion in ciders that have been bottle condition, nucleation upon opening can occur on the sediment in the bottom causing a large eruption in the bottle where the sediment will fly up through the drink and in worst cases erupt out. Again this is perhaps not technically a “fault”, as the flavours of the liquid are mostly unaffected, but if the amount of sediment is high due to poor bottling technique or over priming occurs then this issue is more likely

What does it look like: cloudy flying lees, sludgy globules of sediment in the bottle. Very unsightly in the glass if the bottle is not left to resettle, which can take considerable time as the constant stream of bubbles will keep things floating around.

How does it smell: not something that generally affects the nose

How does it taste: this is dependant on the cider or perry but nobody really wants to drink chunks of dead yeast, it will over power the flavour with bitterness and an unpalatable texture depending on how long the cider has been in bottle.

Film Yeast

Again, not really a fault, and caused by yeast covering the surface of the container, but can lead to fault development. Only an issue in production if on a significant scale as the yeast can start to degrade the cider and lead to acetification or development of ester type flavours. It can also occur in the bottle, especially if it’s still cider or any conditioning is a bit slow to start as these yeast like oxygen.

What does it look like: it’s mainly a visual issue that just looks unsightly, in most cases will break up and sink to the bottom if you turn over the bottle.

How does it smell: this can depend on how sever but over time could create acetic or ethyl acetate (see above) odours.

How does it taste: If left unchecked in the tank stage they can lead to faults listed above, however in the bottle this process can take a little longer or might not occur at all. James has had issues with a batch of cider having film yeast that will not go away, yet no impact on the flavour has yet occurred after 2 years in the bottle (it’s a little experiment he’s conducting).

In summary

The above is a start on some of the more common faults, off flavours and issues drinkers and makers will come across with full juice cider. Most are present in small quantities and can add complexity to flavour, but once one steps out of line and starts to dominate then it can over power and ruin a good cider.

It is worth noting that there are some basic actions cider makers can and do take to thwart these intruders from gaining a foothold on their ciders and perries. Firstly is cleanliness [Ed: second to godliness]. We cannot stress enough the importance of cleaning and sterilising in preventing unwanted off flavours and faults.

Second is keeping your tanks sealed, Oxygen is the enemy at all stages except the very beginning.

Third is Sulphites and although cider does contain naturally occurring sulphites at low levels, you need a bit more if you want to guarantee knocking out unwanted yeast strains or bacteria. Depending on their methods, makers will use varying amounts of sulphite, including zero, and will add at different stages; some at the start and some at the end, even some in between. But there is a threshold that total additions have to be below — of 200ppm (parts per million).

pH also has a part to play and once you get higher than pH4 the risk is magnified, hence some makers will add malic acid to adjust the acidity. Apple juice has malic acid in it, which is what gives cider its acidity. However the amount varies between varieties, with culinary and dessert fruit having more or at least perceptibly more compared to cider varieties. Certain pear varieties, especially culinary pears, have juice which is higher pH and therefore lower acidity.

The important point for us here at Cider Review is that we have an open conversation about these things. We shouldn’t shy away from giving or receiving feedback as it will help the cider industry to grow, develop and improve.

If you want to read more about “when things go wrong” and the science behind it, then have a read of Andrew Lea’s website.