Starch and Gelatinization 101

by Charlie Scandrett,

Posted to HBD 4/7/97

Starch is a non homogeneous polymer (i.e.a complex of simpler bits), a "polysaccharide" of thousands of simple sugars in a similar way that fats are polymers of aliphatic acids, proteins of amino acids and tannins of simple phenols. Actually most of organic chemistry is easier to understand if you imagine God spending most of creation week playing with a carbon based Leggo(tm) set.

When a solid polymer contacts a solvent, the first stage of interaction is to form a GEL. With enough solvent it then forms a SOL.

polysaccharide >> gel <<>> sol

The gel/sol interaction is reversible, with increasing water and temperature and enzymic activity favouring the sol. The gel is a COLLOIDAL structure, that is it has interparticle bonds(usually hydrogen bonds) of lower potential energy than starch in true SOLUTION. Thus enzymically unconverted mash starch extracted by lauter will form a gel haze by complexing when the boiled wort is cooled and the lower thermodynamic condition is favoured. This is called "starch haze".

"Simple" starch granules are very individual in structure and content (snowflake phenomena) and vary from 2-100 microns in size. A simple granule contains one nucleus. A "compound" starch granule has several nuclei and a rigid matrix structure.

Starch is insoluble in cold water but in warm water it swells until "gelatinisation temperature" when is *begins* to lose structure and leach out compounds. A single granule will gelatinise over a range of ~2C but a sample of complex starch grits or particles will have a 4-10C range. Sucrose in solution will raise the gelatinisation temperature of starch by reducing its swelling. So in a concentrated mashing situation, the conversion of more easily gelatinised small starch particles to simple sugars can slow the gelatinisation of larger less gelatinised particles, extending the range.

The *laboratory* gelatinisation temperature of barley *malt* starch is 64-67C (147-153F), unmalted barley is a couple of degrees lower. However as I have pointed out above, this range can be extended by malt modification, crush, mash concentration, and even the weather down at the barley farm. Even after "gelatinisation", there is further breakdown of the starch granule's matrix structure. Technically gelatinisation is not complete until there is no structure left at all. The fact that *infusion* mashes do not fully gelatinise malt starch is shown by the slight but consistent higher yield of *decoction* mashes.

I think inadequate time between 70C and 75C, inadequate stirring and coarse crush are main reasons for ungelatinised, therefore unconverted starch.

Because it inhibits lipid and polyphenol extraction, I always try for a coarse but even crush. Flour is of little interest to me. There are three basic methods to ensure advanced gelatinisation and thus good extraction of sugars and flavours. (Yes, degrees of gelatinisation affect flavours in baking.) The unique flavours of decoction mashing found in lagers are, I believe, partly due to the release of compounds by complete gelatinisation. Pilseners are the lightest beers brewed and have these lager flavours, so they cannot be due to Maillard reactions alone because a good indicator of amount of melanoids is colour. Darker lagers and ales are both flavour-affected by Maillard reactions, but Pils is unique in that it is decocted but light, and still somewhat malty. Anecdotal experience is too subjective for me to empirically confirm this.

1/ The 40C rest of Fix's 40/60/70 program is a beta glucan rest. It allows glucanases to break down gums that impede gelatinisation. It also allows good hydration of the starch cells for later swelling to gelatinisation, while being below optimum protease and amylase activity ranges. This means you can control your protein and fermentability profiles independant of this rest. The speed of SG rise at 60C will confirm its efficacy.

2/ In single step infusion mashes optimum extract is obtained at ~68C (155F), while optimum fermentability at ~65C (149F). This is partly dependant on the greater gelatinisation at 68C and greater beta amylase activity at 65C. Even in a single step mash, stirring and a steady rise to mashout at >75C after sachrification will give the alpha amylase a chance to work on the last bit of gelatinisation. Typically 15 minutes doing this will be a noticable improvement on using just a single still rest and immediate lauter. Start the rise after the iodine test shows existing gelatinised starch has been sachrified. If you wait until all amylase has been denatured at some rest in the high 60's, you might only create starch haze. You could withold a portion of the mash at 65C to add back after an extended mashout. This would convert the last of the gelatinisation.

3/ Decoct the grain bed. Removing the thin enzyme-rich wort and boiling the rest is the simplest method. Stirring is of extra importance here. A pH below 5.5 is also critical to avoid astringency.

There is a fourth method which I am investigating. Auto Decoction. I have built experimental and production mash tuns which are pressure vessels (25, 100, and 2600 litre cookers) with vacuum guages and mechanical stirrers. I mash in at 58C for a protease and hydrolysing rest of 15 minutes. I then reduce pressure with an adjustable release valve and a vacuum pump and apply heat until the mash BOILS at ~65-70C! (About 0.24 atmospheres) The speed of SG rise after 10 minutes of this is spectacular in laboratory trials. I am decocting and sachrifying at the same time!

Charlie (Brisbane, Australia)

Appendix: April 22, 1997



The purpose is more advanced gelatinization for extract and *flavour* release, and the formation of hot break in the grain bed to complex with lipids and polyphenols during recycling. Denaturing enzymes is not that important with the exception of the staling lipo-oxygenase enzyme in pale lager malts kilned <70C. An added advantage is a hotter more permeable lauter. Sparge water temperature is a separate issue. Because it is a more effective solvent than runnings, the danger of the less polar complex polyphenols being extracted suggests staying below 75C and pH <5.5.


I usually mash in at 58C for a HWMP proteinase rest. I then rise at 0.5C/ minute to ~68C for sachrification rest. After conversion (or nearing conversion, I don't always check) I withdraw about 1/4 of the mash *liquid* at ~68C in an uninsulated container and mashout the remaining mash at 77-78C for 20 minutes. Because I use steam injection, the rise to mashout is very quick. Boiling water infusion mashers could do this quickly. RIMS and external heaters will need more time for this rise. After 20 minutes the withdrawn portion has cooled to about 60C and after the mashout portion has cooled to about 73C, I recombine them for a conversion tempertature of about 70C. After 10-15 minutes I get complete conversion and reheat the whole mash to 75C. I recycle for 15-20 minutes by pump, then lauter.


33 or more points extraction is fairly easy, but I have a large lauter tun and this method does take more time. After Lauter, with a short, stirred thick boil (i.e. a little above 100C) of first runnings, I get an authentic Pils maltiness. Great care is taken to prevent scorching. With a longer (30mins) pressure boiling (~125C) of first runnings, I get an authentic bock/ double bock maltiness. The results are definitly smoother than conventional decoction.

This is no-decoction lager mashing, hence "psuedo-decoction".

Charlie (Brisbane, Australia)