Although not strictly technically correct, the essence of what is said in that article by Mark Noorman is worthy of consideration.
Proteins indeed do denature with high temperatures; time/temperature dependent.
Steaming can, as with boiling (given enough time) render a protein denatured and ruin enzymes and amino acids which makes them undetectable/unattractive to the fish. From an anglers point of view; its the amino acids which fish can detect not the enzymes themselves, enzymes are what makes digestion possible and along with hydrolysis (facilitated by enzymes), breaks down polypeptide bonds. This is important from a fish welfare point of view - for without the necessary enzymes, fish have to call upon their own bodily reserves (if present, in ever decreasing quantities throughout their short life times) to attempt digesting junk-food proteins. I think its fair to say; that if the amino acids are ruined by heat, and therefore not detectable by fish olfactory (other than feeding by sight alone); then its probable they may refuse to take the bait in preference to another knowing that its hard for them to digest? Evidence of their innate ability to do so certainly seems to suggest they have a preference.
Alcohol containing flavours/glugs are another denaturant too - but that's a whole new beef of mine!
Its true that steaming reaches higher temperatures than boiling alone, but in order to do so, the boiling water has to first evaporate and turn into pressurised steam, steam creates pressure within its container and penetrates the boilie and all the while continually subjecting (and saturating) the ingredients with moisture. This makes them soft throughout the process and difficult for the bait maker to realise they are "done" - neither will they pass the float test if you were to drop them into water due to their increased density. Boiled boilies should be put into boiling water for a minute or until they float, steamed boilies saturated with water usually (depending on ingredients) do not float and also take much longer to dry with an increased chance of mould growth.
The time it takes for the water to turn into pressurized steam will have already exposed the boilies to increasing temperatures for longer periods due to the fundamental design of a domestic steamer - which is designed, for safety reasons, to allow steam to expand and pressure to escape. This is especially true of all domestic steamers, (including pressure cookers); the boilies would need to be exposed to increasing temperatures for longer periods until the temperature required is reached to cook the egg. This is equivalent of dropping freshly rolled boilies into warm not boiling water. Its also important to realise that even prolonged exposure to lower temperature/pressurised steam will penetrate to the core. Boiling on the other hand, although not perfect, is of lower temperature and will mostly denature the exterior of the boilie, but at least after some time spent in the lake it will allow those attractants to leach after the outer layers start to breakdown.
Over exposure to steam is the same as over boiling, both have a denaturing effect. The only difference is that with boiling its generally only the outer protein layers which are significantly denatured leaving a softer more soluble inner core of paste.
The hottest temperature possible for the shortest time (preferred) will leave a thinner denatured outer layer. In that regard boiling is the best solution if your looking for faster breakdown times with maximum natural attraction and digestibility.
