Yeast is a necessary component in wine-making, but at a certain point, the yeast fermentation must be stopped. When fermentation is finished, some yeast still remains in the wine. If it is not killed before bottling, it can result in further fermentation, turning your hard work to vinegar, breaking bottles or blowing corks. There are four ways to kill the wine yeast to stop fermentation.
Let the yeast starve. In this method, you simply let the yeast consume all of the sugar until there is nothing left to eat, at which point it simply starves. This will produce a dry wine. To get a sweet wine, stop fermentation sooner, before all the sugar has been converted. You may also sweeten the wine again after all the yeast is dead, without fear of restarting fermentation.
Heat the wine to 150 degrees Fahrenheit for 10 minutes. The yeast cannot survive this pasteurization process. Be aware that the cooking method of killing yeast can yield unpredictable changes to the taste of the wine.
Add sulfites or sorbates (usually Campden tablets and potassium sorbate) to the wine. This is how commercial wines are usually stabilized, but keep in mind that some people are allergic to sulfites. Use one crushed Campden tablet per gallon of wine. Use a half teaspoon of potassium sorbate per gallon of wine.
Let the alcohol kill the yeast. Yeast can only live in an environment with a certain amount of alcohol. Wine yeasts in particular can only survive up to about 6 or 8 percent alcohol.
Wine-making is an art as well as a science. You may have to experiment to find the best solutions for you and your particular setup.