I'm afraid Mr. Kaiser was misinformed when he wrote that. There is always unconverted starch even in spent grains. Large commercial breweries routinely perform lab analysis on the spent grains to determine exactly how much unconverted starch is left to make sure it stays below certain values.
Decocting grains, even in the final step when all starch is fully converted but only in the liquid part, will release some starch which cannot then be converted any more and this will affect beer quality to some extent. That's the reason why decoction to mash-out temperature must always be performed by pulling liquid only. It's also the reason why efficiency will go up when performing a decoction instead of a simple infusion as decoction is more effective in releasing as much of the starch as possible from the grains.
If you're still unconvinced, when performing an iodine test before mash-out try performing it with some spent grains in the sample. You're guaranteed to always have a positive iodine reaction from the grains even when full conversion has already been achieved.
Well, a great subject, worthy of doing some research.
I went to check Mr. Kaiser's sources, the main of which was
Abriß der Bierbrauerei by Ludwig Narziss, a great classic book I happen to have in my library too. In Punkt 2.3.3.3 Narziss suggests five ways to perform a single decoction. The first is like this: Mash in at 35-37C, heat to 50C in course of 20 mins. and keep there for 15-30 mins.; then raise the temp in course of 15 mins. to 65C and keep there for 30 mins. Then draw the liquid part of the mash to another preheated kettle, while heating the thick part for full saccharificaton at 68-72C [exact dextrinization rest time is not specified - appaprently till the negative iodine test] and then boiling it for 15-30 mins. Then mix the boiled thick part into the liquid part and then start the filtration.
Then he adds (my exact translation): "
It's also possible to draw the main [liquid] mash after [the whole wort] saccharification at 70C, however there might be a risk of weakened amylases not being active enough for full saccharification of significant quantity of starch, extracted into the solution during the boil".
So, both you and Mr. Kaiser are right. He says it's possible. You say it isn't because of lot of starch coming into the wort. And Dr. Narziss says it's possible, but risky because of lot of starch coming into the wort.
And what Mr Protos sez? He sez he has repeated this Mash-Out Decoction For Dummies for 12 or 15 times. Probably he was getting a lot of starch coming into his wort. Probably his Weyermann Malz amylazes were active enough to convert even that additional starch as he'd never noticed any detrimental effects of this simplest single-decoction on his beers. Apparently, many times he was unknowingly nearing the risky line but always somehow managed to stay at the safe side.
Next time I do this simple decoction routine (and I will do, as it has never failed me) I will do an iodine test to see what really happens in my mash, so thanks for the suggestion!
***
...But see what Johannes Olberg says in 1928 on decocting Kölsch:
Or after saccharification of the mash, about a third is left in the lauter tun while the other two-thirds is brought to the boil in the kettle and returned to the lauter tun to mash out at 76ºC.
It's from
an article in Ron Pattinson's blog, to which (the article, not the blog) Hanglow turned my attention just recently in another thread here on HBT.
Then, we might see that even ~100 years ago, with their worse malts, they in Germany weren't scared too much of starch and did exactly what Protos sez he duz
