Malolactic fermentation can only occur at temperatures higher than 68 degrees Fahrenheit, so keeping wine cold is one way of preventing malolactic fermentation. Another method is early racking; malolactic fermentation requires a specific pH and won't work with wines that have a very low pH (below 3.1).
Malic Acid is one of the main acids found in the acidity of grapes. Its concentration decreases the more a grape ripens. Malic Acid provides a strong link to wines tasting 'flat' if there is not enough. If there is too much the wine will taste 'sour'.