Spectrophotometric determination of malic acid by enzymatic assay. Malic acid is a critical parameter to measure to ensure that your wine is going through its malolactic fermentation. Secondary fermentations can slow down or become "stuck" thus delaying cellaring activities such as sulfuring. If you are making a non ML wine it is important that you keep an eye on the malic acid levels to ensure a malolactic fermentation has not started.

Is your wine smelling a bit off? It might be acetaldehyde. Bring in a sample for testing.