If your wine is clear, stable, and free of CO2, it's ready. Clear means free of particles that could later fall out of suspension and leave a deposit in the bottles. Stable means finished fermenting and with enough sulfites (SO2) present to prevent oxidation and spoiling. Free of CO2 means that although the fermentation may be finished, a wine can still be saturated with carbon dioxide. If it is, it will go into the bottles with the carbonation intact, and depending on the conditions, could expand and push the corks out (or worse, break the bottles), or provide you with the dubious pleasure of drinking a sparkling wine that’s supposed to be still (sparkling Merlot , anyone?). To get rid of CO2, stir your wine.
The Clean Bottle Express™ Wine DeGasser or the Stainless Steel Mix Stir are excellent tools for this purpose. When the fermentation is finished, most people add fining agents, and this is when vigorous stirring is called for. Like shaking up a soft drink, vigorous stirring chases the bubbles out and not only prevents the wine from being fizzy in the bottle, but also helps the fining agents to work better. If you’re not using fining agents, make sure your wine is free of CO2 before bottling.