Measuring Malic Acids
We measure the concentration of Malic Acids in wine to monitor the malolactic fermentation. In malolactic fermentation, malic acids are converted to lactic acids – this helps shape a wine style and character and its aging potential. We used two methods to confirm the successful completion of the malolactic fermentation:
Paper Chromatography, which is time-consuming,
Chemical Test, which is only very approximative, and
Another accurate measurement of malic acids is possible with enzymatic test kits, which use spectral analysis (similar to what we use for measuring phenolics) – however, we never tried it.
Paper Chromatography
Paper chromatography has been employed for decades to visualize molecules of different weights in a solution. First, tiny dots of the sample wines are placed along the bottom of a chromatography paper; then, the sides are clipped together to form a vertical cylinder. The cylinder is placed into a jar holding a chromatography solution and capilar forces push the solution up to the top of the cylinder, dragging the malic acid and lactic acid molecules with them. Malic acids, heavier than lactic acids, will not travel as far up the paper. After a day of standing in the chromatography solution, the paper is removed from the jar and dried. Once dried, traces of malic and lactic acids become visible at different heights of the paper. When there is no longer a trace of malic acids, the malolactic fermentation is complete.
Chemical Test
Accuvin (www.accuvin.com) sells an economical kit to get approximative measurements of Malic Acids in wine. The kit includes sampler tips and test strips, which change color within 5 minutes of applying a 20-micro-liter sample. Matching that color with a reference chart allows us to estimate the remaining malic acid concentrations [>500, 100-500, 30-100, and <30 mg/L]. The goal is to reach <30mg/L. The cost of the kit with five samples is around $30.
Since 2019, we have used OenoFoss to measure Malic and Lactic Acids
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Last updated: May 16, 2023