Nothing, just as there’s nothing wrong with teaspoons. The multi award winning brewer who heads up the Brewtan division at Ajinomoto uses teaspoons. That’s good enough for me.
From my understanding, the main point of protection you get from BTB is the prevention of downstream staling reactions and the chelating of metals.
So it is extremely useful for just those reasons. Many people have been combining it with Metabisulfite and even AA with great results. They all having differing mechanisms that are complementary. Some companies offer pre-packaged mixtures of the 3. Antitoxin SBT in particular uses KMeta/AA/Gallotannins.
Long story short, BTB isn’t an Oxygen scavenger or a neutralizer, although that doesn’t diminish its usefulness one bit.
BrewTan B is not an “oxygen scavenging chemical”. It may reduce protein (enzymatic) and metal ion based oxidative effects but not those caused by free oxygen in solution.
BrewTan B (BTB) is a tannic acid containing gallotannins. These gallotannins bind with certain proteins, specifically those from the proline and thiol groups - that participate in certain enzymatic oxidative reactions and reactions with heavy metals, and drop those proteins and metal ions out of solution. Chelating is the term used for bonding with metal ions.
Sulfites and Sulfides - including Sodium Metabisulfite (SMB), Sodium Sulfite, Sulfur Trioxide and Sulfur Dioxide are oxygen scavengers. They react with free oxygen in solution to produce various byproducts such as Sulfur Dioxide, various sulfates and sodium salts.
Ascorbic Acid (AA) is an oxygen scavenger but has the side effect of producing oxidative products (ions which cause further oxidation such as hydrogen peroxide) when it reacts with the free O2 in solution. It thus requires those oxidative products be reacted with some third party such as Sulfur Dioxide.
Hence you have the so-called “Trifecta” mixture of SMB/AA/BTB which happens to be made commercially in a product called “Antioxin SBT”.
Basically your experiment tested the reduction or elimination of protein (enzymatic) and metal ion based oxidative reactions not the reduction or elimination of oxygen based oxidative reactions. It would be interesting to conduct three of these tests 1.) Eliminate or reduce the protein (enzymatic) and metal ion based oxidative reactions 2.) Eliminate or reduce the oxygen based oxidative reactions and 3.) Eliminate or reduce both protein (enzymatic) and metal ion - and oxygen based oxidative reactions.
I’ve been using BrewTan B (off and on, mostly on) for about 2 years now in both the mash and the boil. I think, if there is a difference, it is something you will see down the road after packaging. I do notice a difference in clarity initially so I have chosen to continue to use it. I would recommend dissolving it first before the mash as well as the boil because it gets very clumpy (unless, in the experiment, you were dissolving it in the strike water.)
It is very expensive so I’d love not to use it but I do believe it may help with shelf life. But OTOH it is very hard to judge that on the capacity that I brew on.
The only question I have about the experiments is - why on the Earth would any one ever brew a CDA?