Where does sediment come from?

Every week this month, we will be answering your #WednesdayWineQuestions. To send us a question, you can respond to a #WednesdayWineQuestions post on our Facebook page or simply email us here.

Q. I’d be interested to know why you get sediment in some wines and a lot more in some than others. (C. Millward via Facebook)

A. (via Katya Sapozhnikova, Wholesale division)

An interesting question and although most people probably think of sediment in red wines, it can be found in whites too. Sediment in wine usually comes in two forms – what are called ‘tartrate crystals’ from tartaric acid which is natural in grapes; or microscopic ‘leftovers’ from fermentation, i.e. dead yeast cells, particles of grape solids etc.

Tartrate crystals are more common in white wines because they form when the wine is exposed to cold temperatures and obviously white wines are generally chilled. Microscopic leftovers are more common in reds – red wines are likely to have extensive skin and lees contact before, during and/or after fermentation.

To avoid the formation of tartrate crystals in the bottle, white wines are often stabilised in the winery i.e. chilled and the crystals removed. Reds are often filtered and fined.

However, with more and more winemakers opting for minimum intervention in the winemaking process, these days many wines are made without stabilisation or heavy filtering. These winemakers believe that such techniques strip their wine of valuable aromas and flavour characteristics. So, sediment even in younger wines may indicate that the wine is made more ‘naturally’.

Sediment is also a by-product of ageing, with ‘phenolic molecules’ combining in the bottle and falling to the bottom; but that would not normally happen in wines that are less than 10 years old and it’s most common in big reds such as Bordeaux, Barolo, Australian and Californian Cabernet Sauvignons and the like.

You asked about variation in the amount of sediment in a bottle. There are many factors which can affect this, revolving around the production and maturation methods.

Finally, it is worth noting that both types of sediment are harmless. In older wines it can just be gritty and a bit unpleasant so it’s a good idea to leave an old wine that you are planning to open upright for at least a day before you open it. That will allow the sediment to fall to the bottom. You can then carefully decant it before serving, stopping just before the sediment gets to the neck of the bottle.