"Meetings of the Institute of Brewing have been held in both London and Birmingham at which the use of flaked oats in brewing beer was dealt with thoroughly, both from the scientific and practical sides. First in respect of the scientific aspect Professor R.H. Hopkins read a paper which contained some very useful figures. As regards nitrogen, always the most important constituent, he found that oats acted as a diluent of the permanently soluble nitrogen and in this he was corroborated by F.E.B. Moritz and H. Heron. The question of oil, of which oats contain two to three times as much as malt, was recognised as being of some concern traditionally and estimations of it in the grist and in the resulting grains tend to show that none of it passes into the wort but it remains behind in the mash tun; analyses occasionally showed slight differences but these might well have been due, in Professor Hopkin's opinion, to the difficulties of sampling. An outstanding feature of flaked oats is its unevenness, consisting of coarse crushed grains and flour; the latter tends to separate readily.
The next item of importance is the extract which to some extent is a commercial one and is closely connected with the moisture percentage which is of technical importance in respect of the possible development of mould. The extract of flaked oats is low compared with that of malt, averaging 55 lb only, with an average moisture of, say, 11%. The percentage of moisture, however, may vary from 8 to 14. With regard to the effect of moisture on mould development, Moritz made some interesting experiments, his results showing that oats with 14% and upwards of moisture was likely to develop mould in a fortnight or so, depending on storage temperature, but that below 13% mould did not develop after 20 days at 80º F. He tried some oats of 15.5% of moisture and found that they gave a strong mouldy smell after 5 days at 80º F. but if some of this same sample of oats was dried down to 12, 10 and 9% respectively, no mould smell developed. Another test on the subject of flaked oats was also made by Moritz. He mashed a grist containing 90% malt and 10% flaked oats, by weight, for the usual period, then boiled the wort without hops and without filtration for half an hour and an hour and a half respectively; cooled under sterile conditions and then forced at 80º F. Heavy bacterial infection developed within three days in the half-hour boiled sample and slight infection at four days with the longer boiled sample. The worts from all malt grist treated in the same way did not show bacterial infection after 17 days. The test was repeated with the addition of hops at the rate of three-quarters of a pound per barrel, and the shorter period of boil raised to one hour, and no infection showed after 10 days with either boiling period. So hops are pretty useful in spite of the depreciation they have lately received. The experiment does, however, show that oats are infection carriers and that they compare so unfavourably with malt is probably because they do not go through so much cleaning as barley gets in the dressing and steeping and some sterilising effect during kilning. W.J. Watkins suggested that oats should not only be carefully selected but also washed before flaking.
Next in respect of the effect of oats on taste; on the whole it seems to be so slight as to be negligible. L.C. Thompson found some gyles of mild ale and one of pale ale to be below the usual fullness, although there was no comment in the trade, and T.E. Grant had a similar experience. G.T. Cook found it very difficult to detect any difference between beers brewed with and without flaked oats, and although he believed there was a tendency for oats to give a softness he confessed it was not possible to pick out such beers blindfold. These results are from large practical brewings; with brewings made in the experimental brewery at Birmingham Professor Hopkins said the prevailing opinion was that oats introduced a slight difference in flavour which was variously described as "more bitter," "softer" and "drier." But although the oat-containing beers could be distinguished the difference from the controls was not great. from all these experiments it would appear that brewers are not going to have any serious difficulties in using flaked oats and the public will not be any worse off."
"The Brewing Trade Review 1943" pages 137-138. (Published in May 1943)
So flaked oats are likely carriers of infection. That's handy to know. As is the fact that oats, in the quantities being used, had little to no effect on the flavour of the beer. Though the flavour descriptions given in the final paragraph do seem contradictory: "softer" and "more bitter.