We've all heard of off flavours, but sometimes it's hard to describe them, and describing them is what you'll need to be able to do to work out the cause and how to prevent them in your next wine.
So what is an off flavour, well it's basically a flavour you don't want in your wine.
A buttery, toffee like flavour in a Chardonnay can be pleasing, but the same flavour in a Pinot Noir can be quite weird. So a good flavour in one wine, can be seen as an off flavour in another wine.
Having an off flavour doesn't mean there is an infection, but it's good to know the different aromas you can get, what they mean, where they come from and are they an actual infection.
So lets delve into some flavours, starting with the one I have already touched on...
1 - A butterscotch, toffee like flavour.
Diacetyl is produced by the yeast as they ferment the sugar. Some yeast produce more than others, and they will make even more if they are stressed by temperature or lack of nutrients.
Diacetyl can be reduced by choosing the right yeast, making sure the fermentation temperature is constant and in the ideal range for the yeast and making sure there are enough nutrients. Once the fermentation is complete leave the wine on the lees for a few days and this will soak up even more of the diacetyl.
2 - A hint of wet dog, wet cardboard or a mouldy damp house.
Having these aromas in your wine is a true off flavour. This is usually found when you open a bottle of wine after a few months or years. This is an infection and there is nothing you can do about it. It was likely infected before it was bottled.
The technical term for this aroma is a Corked Wine or Cork Taint. It has nothing to do with the cork, or little bits of cork floating around in the wine. Its actually caused by a fungus transforming compounds in the wine into a compound called 2,4,6-Trichloroanisole which our nose can detect in just a few parts per trillion.
A corked wine tends to have muted flavours too, so they aren't as fruity or zingy as you would expect.
You can still drink a corked wine and many people do, as it will probably still taste really good, so most people do not realise the wine is corked.
I would say, that if you like the flavour, then drink it.
3 - The smell of plasters.
Yes the plasters that you put on a cut on your skin. The clinical aroma of a plaster in a wine is not a good sign. It's very off putting and very hard to get past. It is safe to drink, but do you really want to hold your nose as you drink your wine?
The antiseptic smell is coming from brettanomyces (Brett), a wild yeast that is found on nearly all fruit. This tends to be picked up more in red wines where you ferment on the fruit instead of just the juice.
At very low levels, brett can impart smoky and spicy notes to a wine, but just a little too much can turn those into antiseptic flavours.
The best way to prevent Brett affecting your wine is good sanitisation and by using campden tablets.
If you find your wine has a just a hint of the antiseptic aroma, decanting it into a carafe and then swirling can allow the aroma to dissipate.
4 - Vinegar.
If you find your wine smells of vinegar, like that which you put on your bag of chips, there might be nothing wrong. Lots of red wines when very young have an acidic vinegary aroma. This is due to age and leaving the wine to condition in the bottle for longer than 6 months this acidic vinegar aroma will disappear.
However, there are times when a vinegar smell wont disappear, and that is when the wine has been infected with the acetobacter bacteria. This bacteria eats alcohol and turns it to vinegar. Then you can still use it in cooking, but it's not good to drink.
Acetobacter bacteria are in the air all around us, so leaving a bottle of wine open on the counter will get infected and turn to vinegar.
This can also happen after the wine has finished fermenting and before it is bottled. Usually because the fermenter has been opened too many times and allowed the bacteria in to infect the wine.
Try and minimise the contact between the wine and the air. If syphoning, make sure to not splash the wine as it is transferred between vessels.
5 - Sherry or Bruised Apple flavours.
This is usually caused by oxidisation. In reds is is easily seen when the colour of red wine turns brown, but it can happen in white wines too, but this is usually only noticeable when you taste the wine, but their colour can darken too. When tasting an oxidised wine, it tastes dull, no zing. Reds tend to have a sherry like aroma, where whites tend to have a dull bruised apple flavour instead of a being fresh and zingy.
When syphoning your wine, try not to cause splashing and try to minimise the air contact with your wine.
When bottling, only leave just enough room for the cork and a small air gap. Too large an air gap will leave too much oxygen in the bottle and can end up oxidising the wine.
If you are opening a fresh bottle, try and drink it within a few days. Leaving a bottle open longer than this can allow the wine to become oxidised.
6 - Eggy, farty, cabbage smell.
Yep, you can get rotten egg aromas in your wine. This is usually due to poor fermentation conditions and the yeast being stressed have released sulphurous compounds to make these smells.
During fermentation, ensure you have a constant temperature in the range of the yeast. Use a good yeast nutrient and leave the wine to fully ferment.
This sulphur is different to the sulphites you add to stabilise the wine.
If you smell this during fermentation, check the temperature and get it constant and stable. Then the yeast will consume and transform these funky smelling compounds into more palatable compounds, and the aroma will disappear.
If you open a bottle and it smells eggy, then decant it in to a carafe and swirl the wine. The aromas may dissipate.
There is also a reaction between silver and dihydrogen sulphide (the compound causing the smell) which can help remove the eggy aromas. Stir the wine with a silver spoon. The silver will blacken and the aroma will diminish. You can polish up the silver again.
7 - Jammy, sweet and reduced.
This is likely caused by too much heat. Storing your wine in the airing cupboard or in a hot shed can cause the wine to suffer heat damage. It's like you have put the wine on the hob and tried to reduce it down, causing jammy, nutty, roasted sugar aromas and flavours.
Heat damage can also cause the small amount of air in the wine bottle to expand and possibly force out the cork and creating a gap for air to get in an oxidise the wine as we mentioned earlier.
Once the wine has been damaged by heat, there is nothing you can do to rectify the fault. If it has not been oxidised, you might like these flavours.
It's always best to keep your wine in cooler conditions, but ideally in a constant temperature. An under stairs cupboard or a cupboard in the spare room. A cellar would be ideal, but not many houses have a cellar.
8 - Mouse / Gerbil / Rat cage aromas.
It already sounds off-putting right? So you might not be able to smell it when you swirl your wine, or even after you have taken a sip, as it takes time for it to develop on your senses. And if it does, it's hard to get rid of.
It's usually caused by too little sulphur dioxide and ageing on the lees. Although lactobacillus bacteria can also create these aromas.
This is normally a problem in aged wines rather than young homebrew wines, however, be mindful to use campden tablets and not to leave the wine too long on the sediment.
9 - Wet Wool.
This usually occurs when the wine has been kept in sunlight. The wet wool aroma is not possible to fix and it is caused when wine is exposed to UV light where the wine has been kept in direct sunlight.
Try and keep your bottles somewhere dark and cool. Do not ferment on a windowsill or a table close to a south facing window. Not only will the light affect the wine, so will the excessive heat from the sun.
Red wine should be kept in green bottles as it is more susceptible to UV light damage as it also bleaches the colour from the wine.
10 - Woody, Oak, Vanilla aromas.
These are usually because the wine has been brewed in or aged in oak, or in the case of homebrew had oak chips added. This isn't an off flavour. It have been added to the wine to enhance its natural flavour.
A lot of wine is made or aged in oak barrels and depending on the type of oak, whether it has been scorched before the wine is added or if the barrel has held other wines or even spirits can make a huge difference to the oak aromas you get in the wine.
11 - Green Herbs, grass, hay, capsicum peppers.
These flavours come from the grape skins and add these green aromas. Grapes that are grown in cooler climates have more, compared to warmer climates.
The herbal green grass / green pepper comes from compounds called alkylmethoxypyrazines, and are common in many wines, adding fresh, summer notes. Most cabernet grapes and sauvignon blanc are rich in the fresh herbal notes.
To minimise the green aromas in your wines, strip the grapes from the stalks, and only use ripe grapes.
The green aromas come from the compounds created by the grape to stop animals eating them before the seeds are ripe. The compounds reduce as the grape ripens.
If you have a lot of aphids on your vines and in turn lots of ladybirds, make sure you wash them off before pressing. Together they have large amounts of alkylmethoxypyrazines (presumably because they eat the sap of the plant) and just a few ladybirds can ruin a small batch of homemade wine.
12 - Pine or Eucalyptus aromas.
If you are growing your own grapes and have them growing near a conifer hedge or eucalyptus tree, then oils from the trees can fall and land on the grapes and stick to the skins, so when pressed, the grape juice picks up these oils and transfers them into the fermenter. As these aromas are very stable, the survive the fermentation and can be tasted in the finished wine.
So if you are growing your own grapes, make sure they are well away from other strong smelling plants as they can transfer their aromas to the grapes on the vine.
13 - Nail Varnish Remover, Acetone, car paint spray.
The aroma is due to a compound called ethyl acetate, which is made by the yeast during the fermentation. Ethyl acetate adds fruity aromas to the wine at low levels.
When the yeast are stressed, or fermented at the wrong temperature, they can create more ethyl acetate than usual and this will cause the nail varnish remover aroma.
Many wild yeasts make high levels of ethyl acetate, so choosing the right commercial yeast that has been bred to give the characteristics you desire in your finished wine is a safe more reliable option.
Following the instructions for that yeast will help create the flavour profile you desire. Temperature, nutrient, pH, using campden tablets in the must to soak up excess oxygen, resisting the urge to keep opening the fermenter to see what's happening can all help prevent excess Ethyl acetate from being formed.
14 - Cooked tomatoes, cooked corn, asparagus, or treacle.
You tend to only find this in aged wines. As the wine ages in the bottle, chemical bonds are made between different compounds and dimethyl sulphide is created.
At low levels, dimethyl sulphide adds delicious blackcurrant and even sweet black olive aromas, but at higher levels, it turns to more of a vegetable aroma.
There isn't much that can be controlled in this process as it depends on the compounds in the wine when bottled.
Luckily the taint caused by dimethyl sulphide is rare and hopefully you'll just get it a low levels and enjoy the delicious blackcurrant flavours and aromas it creates.
15 - Sour.
Think of sucking on a lemon. A wine that is high in acidity when made will keep that high acidity through the fermentation process. A wine that is very acidic can taste sour, but it does depend on the acid that is causing the acidity.
Using citric acid and lemon juice in older wine making recipes has been replaced with other acids, malic and tartaric due to the fruits having more of those naturally compared to citric acid. This creates a softer, less sour wine.
Using grapes that are not fully ripe is usually the reason for excess acid and the cause of your finished wine to be sour.
We can use bacteria to help us reduce the acidity. Fruits have a high malic acid content and this can be quite harsh on the palate. Using bacteria, we can convert this to lactic acid which is much softer and is a lot more desirable in wines.
The good news is that a sour wine can be adjusted to make it taste much better.
The addition of precipitated chalk reacts with the acids and neutralises it, making the wine less sour.
The addition of sugar masks and balances the acidity, making the wine more palatable.
We have written a guide on how to adjust an acidic wine
However, using ripe fruit and checking the pH before you start the fermentation and making adjustments as necessary, means the finished wine will be much more pleasant.
Too much tartaric acid, will cause wine diamonds as the excess acid causes tartaric acid crystals to form. This reduces the tartaric acid and softens the wine. These can form in many wines and is a natural process and the crystals, although they look like shards of glass, are harmless.
There are many other flavours in wine that you may or may not like, but if we haven't listed it above, it's usually a desired flavour.
We hope this guide to off flavours in wine has helped you learn some extra wine making knowledge and use the tips to help minimise these unwanted flavours.