Some brewing methods use a rest to stabilize pH before going to conversion temps. It is not advisable to start mashing above pH 6 or below 4.7. Different malt types will stick at a certain pH if Phytase hasn't been inverted during the kilning process. If the malt does contain Phytase, it becomes denatured at the higher temps used for conversion. Distilled water is used to determine pH of various malt. To say that pH remains the same throughout the process isn't necessarily, true. It depends on the kilning process of the malt and brewing water profile. Beta and alpha have optimum pH ranges where they do their best, so does yeast. Outside of their pH range they become sluggish, resulting in conversion taking a long time. Ale yeast requires a different pH than Lager yeast. If conversion doesn't take place in 20-30 minutes the mash is too thick or pH is out of whack. Enzymes start to denature with time and temperature. Beta denatures under an hour at 149F. Alpha takes less than two hours at the same temp. Making over night mashing mostly useless, except for saturating grain. Mash thickness plays a part in conversion and with attenuation. A pH of 5 may be hunky dory to a brewer but maybe not to other things taking place during mashing phase. Conversion can begin at 130F, even though the mash isn't at the temp for gelatinizing starch. Beta is active breaking up dextrin at low temps. In certain types of malt, Maltase and Dextrinase are not completely kilned off. They are debranching enzymes that make beta and alpha work better. Alpha, basically liquifies starch and breaks up amylose and amylopectin, forming carbs. It releases certain sugars, and a thing called a-limit dextrins. Beta only works on the non reducing end of the stewed up starch chain, creating sugar and b-limit dextrines. Alpha chops up the chain at certain points, creating more non reducing ends. Debranching enzymes create more non reducing ends. The more non reducing ends, the faster beta works.