I see that ol’ amino acid chestnut, Mr. W, who also goes by the moniker of tryptophan, is making the “science of Thanksgiving” rounds here at SB. Over at Chaotic Utopia, Karmen offers a very nice piece on the science of concocting an exquisite gravy. But what good is a gravy worthy of peer review, I ask you, if the mashed spuds which are to receive it are a gluey blob reminiscent of grade school paste?
Sadly, far too many cooks commit the heinous act of overmixing boiled potatoes. With the goal of creating a smooth puree, the cook whirls stainless steel beaters through the cooked root vegetable for just a bit too long and a sticky glutinous mass is the result. How might this sacrilege be avoided?
The answer is the potato ricer.
Potato tubers, and here I refer to Solanum tuberosum, store their starch as amylose and amylopectin. Amylose is an unbranched polymer of repeating D-glucose subunits linked by alpha 1,4 bonding. Amylopectin is formed by non-random alpha-1,6 branching from the amylose base polymers. An amylopectin molecule may contain as many as 2 million glucose units. The overall structure and crystalline packing forms of amylopectin are illustrated in this excellent summary of the bio-physical chemical properties of amylose and amylopectin. This is but one chapter of Martin Chaplin’s (London South Bank University) extensive compendium on water’s structure and properties.
As illustrated in Professor Chaplin’s essay, amylopectin molecules pack radially in starch granules. The structure of starch granules from many botanical sources has been studied extensively. The size of the granules range from 5-85 μm, and even have different shapes: elliptical, cuboid and spherical. Functional properties of the granules vary with size classes with larger granules having a higher amylose content and lower hydration capacity (ability to take up water).
The best potatoes for mashing are those varietals whose starch granules contain a higher proportion of amylose, the straight chain polymer, which packs differently than amylopectin (see Chaplin’s article). Russet Burbanks are a prime example of a good masher. To further ensure a fluffy result, the integrity of the starch granules must be taken into account. Some release of the starch polymers is needed for the smooth texture, yet too much shear force as applied by whipping the potatoes with an electric mixer will flood the puree with too much starch polymer, hence the glue-like consistency. Pressing the cooked spuds through a ricer is more gentle. With less shear force, a higher proportion of potato granules is left intact, and yields a fluffier, and more palatable, result. Hot milk and butter, roasted garlic puree, chopped scallions or chives may then be gently folded into the hot “riced” potatoes.
If you’re going to go to the trouble of applying robust science to gravy-making, then please do the same for your mashed potatoes.