Hello George, Mark, and everyone-

The quick and dirty explanation for why starch grains survive in archaeological sediments is the same reason why any organic remains survive in an archaeological sediment - anaerobic conditions.  If no organic matter survived, we would not be able to locate middens, post molds, or pit features using "dark" or "stained" soil.  Starches do not survive in great numbers in all archaeological sediments.  For example, leached or highly oxidized soils do not typically contain ancient starch grains, although they often survive in the cracks and crevices of lithic and ceramic materials buried in the matrix.  Starches do survive in other conditions, however, sometimes in very impressive concentrations.  The best preservation that I have seen thus far is from an Andean site where the sediment was highly organic and burial happened fairly quickly.  Thus, anaerobic conditions occurred rapidly preserving thousands of starch granules in situ.

It is unclear to me why there seems to be a widespread notion that starches are easily degraded.  I have relied on the experts on starch digestibility - the food and nutrition scientists - and if you delve into that literature, you will find that starch in its unaltered, native form is considered to be chemically inert.  It takes a lot of energy to make starches degradable or digestible, and this is why we cook our food.  Cooking breaks down the semi-crystalline structure of starch and makes it bioavailable.  In some places, mechanical pounding is used in the same way (e.g., fufu in parts of Africa).  Without this processing, it is extremely difficult to digest starch, and from the literature, it is my understanding that this is true for all biological organisms.  So if a bacterium has a choice between a fragment of leaf or an intact starch grain for a carbon source, its more energy efficient choice will be the leaf.  (Assuming optimal foraging theory can be applied to bacteria, of course.)

An assessment of whether or not starch is a modern contaminant in a site should be completed just as it is with any other component of a site, taking into account disturbance as well as modern activities.  I suppose that we are lucky in that many of our sites have not been occupied since abandonment, and there has been no farming since the archaeological sediments were deposited.   In an context such as this, it would be difficult to explain the presence of starches by modern contamination, particularly if the crop plant has not been cultivated in the area for thousands of years. 

Please keep in mind that this is a very brief and simplified explanation for the complexities of taphonomy, but I hope it helps.

Linda Perry 



> Date: Thu, 6 Mar 2008 18:33:06 +0000
> From: [log in to unmask]
> Subject: Re: starch grains
> To: [log in to unmask]
>
> Dear members,
>
> I agree with George, would someone please explain
> how starch survives in archaeological sediments? I too have heard
> the opinion that they are modern contaminants.
>
> Best wishes,
> Mark Robinson

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