Knights of the Mashing Fork

Darrell in Plattsburgh asks,

When doing a CAP: I recall that in gelatinizing the corn it was suggested that one add some malt as well. Why is this?

Malt isn't used to achieve Gelatinization, but to avoid it's evil doppelganger, Retrogradation.

Gelatinization of starch involves unravellings and hydrating the huge and highly branched amylopectin molecules. Grain starch granules, for instance, often contain a single amylopectin molecule with thousands or even tens of thousands of glucose units.

Anyone who has ever made gravy or used starch as a thickener for soups of pies realizes the gelatinized starch traps a large amount of water and thus forms a gel. If the amount of water is small then gel is thick and is insoluble when more water is added. It sets like glue (and has been used as glue for centuries). Even in somewhat thinner gels, given time, starch molecules form closed 'pockets' which are not soluble. If you've seen grist 'ball' or starch get lumpy, then you've seen a macroscopic version of the same problem. Bread staling is actually retrogradation too. Less water, higher pH and lower temps all encourage retrogradation.

If starch retrogrades, then there is little hope of ever mashing it into fermentables.

Most folks don't appreciate that you need something like 20 times the mass as water to fully hydrate intact grain amylopectin and avoid any retrogradation. That's around 6qt per pound (~12L/kg) for typical grains .... and that's a ridiculous and impractical amount.

The basic problem is that a *lot* of water is trapped around the highly branched amylopectins. One way to reduce the water requirement is to cut the amylopectins into small bits which can't trap as much water. Alpha-amylase does this nicely.

The goal for a CAP is to bring the raw corn above it's gelat temp (typically 70-75C) along with a small amount of pale malt [malt has far more alpha-amylase than needed for self conversion] and then give it a decent rest at that temp. The simple sugars also help reduce the water trapping issue.

Snipping up the mega-dalton grain amylopectins with alpha-amylase to prevent retrogradation with a modest amount of water is the point of the malt in a cereal mash.

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