Malo-lactic Analysis by TLC

Here are a couple of ciders analysed on a TLC (thin-layer chromatography) plate, to check for the malo-lactic fermentation.  This is carried out in cider by specialised bacteria which convert the original malic acid to lactic, generally as the cider matures once the yeast fermentation is completed.  This reduces the total acidity (since lactic acid is a mono-basic acid whereas malic is di-basic), and carbon dioxide is lost in the process. So the cider tends to become slightly gassy again.  Desirable strains of these bacteria also soften and round the cider by producing new flavour compounds .  It is now possible to buy various strains of ML bacteria commercially and add them to the cider, rather than waiting for them to work of their own accord.
 
 

TLC plate
The cider samples are spotted at the bottom of the special silica plate, on the pencil line, and they move by capillary action up the plate when placed in a jar of solvent.  After drying, the plate is dipped in an indicator (bromo-cresol green) and the acid spots are revealed as pale yellow on a darker background. Lactic acid moves the furthest (the left hand track) and malic the least (the right hand track).  The blue spots that stay close to the origin are due to the natural potassium salts present in the cider.  The pale yellow spots are quite faint and may not be evident at first glance - but they are there, trust me!

So what you see here is that the left hand sample (one of my own, as it happens) has gone entirely ML with no malic acid remaining.  The cider on the right, by comparison, has all its original malic acid with only a trace (if at all) of MLF conversion.
 
 

Technical Details

Plate:  Macherey Nagel Polygram Sil G Cat No. 805012

Spot Application:  2 microlitres, dried, and then applied again

Elution Solvent: Toluene + Acetic Acid + n-butyl acetate 2:1:1

Indicator:  Bromocresol green (sodium salt) in ethanol (0.2%)

Reference:   Australian Grape Grower and Winemaker January 2001 (doesn't display in Netscape 4.6 but OK in 7.1!)
 
 
 
 

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Last updated 29.9.2002