Sometimes, what appears to be a crystal clear bottle of wine can create a film of sediment on the inside of the bottle. How can that be if it was crystal clear?
When you bottle your wine, there are chemical processes that take place during the ageing process, these are normal and can create sediment, but more about that in a mo.
SEDIMENT - Firstly, before you bottle your wine, you can make sure the wine is crystal clear by filtering it. Even if you have used finings on your wine, it may look clear, but there are still microscopic particles and yeast floating around. Over time, these settle to the bottom of the bottle and form a film. Usually when you move the bottle this sediment is disturbed and you can see the cloud start to swirl in the bottle.
This is easily fixed by filtering your wine before you bottle. The filter collects the microscopic particles and polishes your wine.
PROTIENS - Now, in your wine, there are proteins floating around that are part of the wine and can't be filtered out. If the temperature of your wine fluctuates during storage, these proteins can activate and become opaque causing a haze.
Bentonite Clay is fantastic at soaking up excess protein, so adding Bentonite before bottling, while in bulk storage, can help prevent a protein haze developing.
COLOUR & TANNIN - In red wines, there are colour compounds and tannin. Over time the colour compounds can coagulate and so can the tannins, again dropping out of suspension. This can form an interesting sediment that due to the darkness of a red wine cant be seen until you pour the last glass or 2 from the bottle. This is why it's a good idea to use a carafe when opening a bottle of red that's a few years old.
When bottling, try and minimise the splashing, and keep the gap between the cork and the wine as small as possible to minimise the amount of oxygen as this can be a cause of the pigmentation and tannin coagulation.
CRYSTALS - Wine Diamonds, aka tartrate crystals can form if a wine is rich in tartaric acid. These look like little shards of glass in the bottle and can form on the sides of the bottle. Sometimes you don't see them, but only realise they are there as you suddenly get a crunch as you take a sip. Again these are perfectly natural and harmless. In fact their presence means your wine will have lost some acidity and softened.
You can minimise wine diamonds by cold stabilising your wine whilst in bulk storage before bottling. Cold stabilising means holding your wine at near freezing temperatures for a few weeks, but this can be difficult for the homebrewer.
So, now you should have a little more insight into why your wine may have sediments in the bottle and how to take steps to prevent them. Using Bentonite when bulk ageing, Filtering your wine before bottling, Reducing the amount of oxygen (air gap) in the bottle and trying to keep your stored wine around 12-14°C (cellar temperature) will help prevent sediment, proteins and crystals.
Cheers & Happy brewing
Davin