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)
This is no-decoction lager mashing, hence "psuedo-decoction".
Charlie (Brisbane, Australia)