How to know if a wine has completed its malolactic fermentation

How to Know if a Wine Has Completed its Malolactic Fermentation Malolactic fermentation (MLF) is a critical process in winemaking that not only affects the sensory profile of the wine but also helps in stabilizing it. Unlike alcoholic fermentation, which converts sugar into alcohol, MLF involves the conversion of malic acid into lactic acid. This transformation significantly impacts the taste, texture, and aroma of the wine. Determining whether a wine has completed its malolactic fermentation is crucial for winemakers to ensure the desired outcome. In this article, we will explore the signs and methods to ascertain the completion of MLF. 1. Understanding the process: Malolactic fermentation usually occurs after alcoholic fermentation and is typically carried out by lactic acid bacteria, mainly Oenococcus oeni. These bacteria thrive in a wine environment rich in nutrients, pH, and temperature. During MLF, the sharp and tart malic acid present in grapes gets converted into softer-tasting lactic acid, imparting a smoother mouthfeel and reducing acidity. 2. Monitoring pH and total acidity: Measuring pH and total acidity regularly can provide useful clues about the progress of malolactic fermentation. As MLF progresses, the pH of the wine tends to increase, and the total acidity decreases. By tracking these values over time, winemakers can identify shifts in acidity that indicate the completion of MLF. However, it is important to note that pH and total acidity can be influenced by factors other than MLF, so they should not be the sole criteria for determining the fermentation's completion. 3. Analyzing malic and lactic acid levels: Testing the malic and lactic acid levels in the wine is a more direct method of assessing MLF completion. Initially, wines have relatively high malic acid levels, but as MLF progresses, the malic acid decreases, and lactic acid becomes more prominent. Analytical techniques such as chromatography or enzymatic assays can be employed to accurately measure these acid levels. A significant reduction in malic acid and a corresponding increase in lactic acid confirms the completion of MLF. 4. Sensory evaluation: Beyond analytical measurements, sensory evaluation plays a vital role in determining MLF completion. Tasting the wine throughout the fermentation process allows winemakers to assess changes in flavors, mouthfeel, and aroma. Wines undergoing MLF typically exhibit buttery, creamy, or nutty notes due to the production of diacetyl, a byproduct of the fermentation process. Once these sensory characteristics reach the desired level, it suggests the completion of MLF. However, sensory evaluation should be considered alongside other scientific methods for accurate results. 5. Stabilizing tests: Performing various stabilizing tests can also aid in confirming the end of MLF. One such method involves gently warming a small sample of wine and observing if any additional gas or bubbles are released, indicating active fermentation. Additionally, conducting a paper chromatography test can help detect residual malic acid, which would appear as a distinct band on the chromatogram. These tests provide a visual confirmation of whether or not MLF has finished. In conclusion, determining the completion of malolactic fermentation is crucial for winemakers to ensure the desired flavor and stability of the wine. Monitoring pH, total acidity, and malic and lactic acid levels can provide valuable data throughout the process. Sensory evaluation, backed by scientific analysis, helps in assessing the desired characteristics expected from MLF. Performing stabilizing tests can also provide visual confirmation. By employing a combination of these methods, winemakers can accurately gauge whether a wine has completed its malolactic fermentation, allowing them to refine their winemaking techniques and produce exceptional wines.