?1790 J. Dalrymple 2 London porter-yeast..is prefered..by the distillers.
1878 IV. 1389/2 After which it is run into the fermentation-vat and a mixture of London-porter yeast and quick Scotch barm added.
2000 Re: Difference between Porter & Stout? in alt.beer (Usenet newsgroup) 7 Dec. Flag Porter even uses a recovered porter yeast, I believe,so it's a reasonable attempt at reconstruction.