As an expert sommelier and brewer, I can assure you that it is not uncommon for red wine vinegar to have some solids or cloudiness floating in it. This can happen over time, especially if the vinegar has been opened frequently. But let me assure you, this does not mean that the vinegar is bad or unsafe to use.
Red wine vinegar is made by fermenting red wine. During the fermentation process, acetic acid bacteria convert the alcohol in the wine into acetic acid, which gives vinegar its sour taste. This high acidity makes it a hostile environment for harmful bacteria to survive. So, even if your red wine vinegar has been sitting in your pantry for a while, it is still perfectly safe to use.
The solids or cloudiness that you may see in your vinegar are often harmless. They can be a result of sediment or residual particles from the fermentation process. Sometimes, they can also be a result of the natural compounds in the wine reacting with the oxygen in the air, causing the formation of tiny particles.
If you prefer your vinegar to be clear, you can strain off any solids or cloudiness using a fine mesh strainer or cheesecloth. This will help remove any unwanted particles and give you a clearer vinegar. However, keep in mind that straining your vinegar may also remove some of its flavor compounds, so it's a matter of personal preference.
It's worth noting that the quality of your red wine vinegar may decline over time, especially if it has been exposed to air or sunlight. Vinegar is best stored in a cool, dark place to preserve its flavor and quality. If your vinegar has a strong, unpleasant smell or taste, it may be an indication that it has gone bad. In such cases, it would be best to discard it and get a fresh bottle.
It is normal for red wine vinegar to have solids or cloudiness floating in it over time. These are generally harmless and can be strained off if desired. As long as your vinegar smells and tastes fine, it is safe to use. Just remember to store it properly to maintain its quality.