Malt Whisky Color
Knowing my fifty year enthusiasm for Malt Whiskies, and my life long study of color vision, a friend asked what makes the color of Scotch. After much consideration, the answer is carbon. My friend then replied, but carbon is black. Not so, any material when formed into a complex small structure can “look” black. My favorite demonstration is looking at razor blades. A stack of blades, shiny steel, tightly fastened and observed sharp edge on will be blacker than any black paper you can find. Indeed, soot carbon (SC), or carbon black, is merely a clumping of carbon, which chemically forms a remarkable system of diverse structures – including life forms. Back to Scotch, the color is of course “amber”, and for the same reasons, carbon. It is most easily produced by boiling away the water in a sugar solution, yielding caramel. This color is persistent in nature, honey, maple syrup, beer, brandy, bourbon, even the deterioration of cellulous material as in old paper (pyrolysis carbon PC), said to “yellow”.
Most color we observe is the result of scattering, absorption, and reflection of light, electromagnetic radiation (photons). For now I’ll skip details, the submicroscopic particles in Scotch scatter and absorb light in a way intrinsic to carbon as well as the size distribution of the particles (Mie Solution Scattering). It is well known that the malted barley solution after fermentation and being doubly distilled is crystal clear when it goes to the Spirits Receiver. This clear liquid (mostly ethanol) is aged at least 3 years in used oak barrels to produce the malt whisky. Tradition has the oak as sherry aged before distillery use, but today Bourbon, and other prior treatments prevail. In all cases the interior oak is heavily carbonized, this complex, adsorbent, surface is host to the slow development of complex molecules from which the simple distillate began. The breakdown of the oak into complex sugars that are caramelized is pyrolysis, the source of the amber color. The more complex carbon char overlays this transition layer.
One test of this color process I have made is to take crude petroleum from Titusville, PA, home of the original oil well, and float ethanol over a sample. The result is the color taken up by ethanol from the petroleum exactly matches the amber we admire in malt scotch. This color matching is not by eye but by spectrometer. Indeed, caramel, scotch, and the carbon extract from petroleum give absorption spectra that are simple exponentials with nearly identical slopes. Except for intensity (concentration), caramel, malt scotch, and many other amber colors are identical.
Most color we observe in daily life is selective absorption, in flowers, paints, and dyes; these are mostly subject to fading and change with time. The most abundant color we see is the blue of the sky, the result of scattering, by dust and aerosol particles whose color interaction is only related to their relatively large size. The smaller, approximately 30 nanometer carbon particles (PC , or colloidal carbon) producing the amber color are not subject to chemical change or ultraviolet damage, but are stable for million’s of years as in the petrified tree resin that gives the name “Amber”. I am not competent to do the calculations for the Mie solutions, but have taken spectral data that show nearly exact matches for these amber colors. It is well known that lighter color in maple syrup is more valued for its flavor, as the darker color means more carbon, and less sugar. Sadly this analysis also suggests that color of malt whisky, while such a delight for its gem like dazzle, is largely irrelevant for its flavor.
Why ever did William Faulkner say the color was ‘brown’? This glorious beverage, the product of religious design for decades, the distillation process brought to Ireland, infused thru Campbeltown into Scotland, and developed by two centuries of artistry and craft is indeed “forever amber”!