This is the most confusing of the uses. The one where, rather than describe a specific type of beer, an attempt is being made to conjure up a nostalgic image of Merrie Olde England.
I'll admit that I'm not sure whether this pub really brewed something called Nut Brown Ale or whether they're just doing the Merrie Olde England bit. I suspect the latter, but could be wrong:
"OLD CURIOSITY SHOP."A bit weird that a Salvation Army caption should be brewing. Aren't they supposed to be teetotal?
FOREST TAVERN, MANSFIELD ROAD, NOTTM.
Vide—Large Lamp, The Major Oak."
THE GREATEST NOVELTY NOTTINGHAM IS ELLIS'S "NONPAREIL" NUT BROWN ALE.
Drawn direct from the ancient "Freebooters' Cave," Mashed, Brewed, and Racked by Captain (Salvation Army) Ellis, the last of the Race of Outlaws.
For Bold Robin Hood, in old Merry Sherwood,
Tippled "Nut Brown," with flavour so good.
His jolly men brewed in the merry green wood.
ELLIS, the Collector of Thousands of Local Relics and National Curiosities. Inspection Free to All.
Nottingham Evening Post - Monday 05 January 1891. page 1.
This next one is a clear example of a nostalgic use of the term Nut Brown Ale:
"THE PURE BEER COMMITTEE.
A LINCOLNSHIRE WITNESS.
At the fourth sitting of the Pure Beer Committee, held at Westminster under the presidency of the Earl of Pembroke, the first witness was Mr. E. J. Grummitt, who, in reply to the chairman, said that he was a brewer, and farmed rather largely in South Lincolnshire. He brewed beer for the farmers and labourers in his own district, and branded every cask with a label, " Guaranteed brewed from best malt and hops only." He had never used any other materials than English barley malt, except in the wet seasons of 1879 and 1880, and then he was obliged to use some sugar in consequence of the faultiness of the malt. In good harvests, when they got barley well ripe, there was no necessity to use substitutes at all. He used his own barley and his neighbours', and no foreign barley at all. The character of the beer had been altered in the last ten or twelve years, and they brewed a lighter and a cheaper beer. In Lincolnshire, people years ago liked a sort of nut-brown ale, but they now brewed a pale, light beer. Asked if it was as easy to make the light beer from English barley as it was to make the old hard beer, witness replied that it was. For instance, Bass's, and the great Burton brewers, were buying the very best barleys they could buy in Lincolnshire and the district at as much as 45s. a quarter, and if they use substitutes they would not go to the expense buying this barley. He did not know that the Burton brewers used nothing but English barley malt, but he believed the quantity of substitutes was very small indeed, if they used any. When hops were very dear a few years ago substitutes were used very largely, but of late years very little in the way of substitutes had been used. The light beers could be easily and economically made solely from hops and English barley malt. A brewer friend of his bought foreign barley at from 18s. to one guinea a quarter, and used one-half foreign barley and one-half sugar, and sold this thick gluey kind of beer as "Welsh ale" to dockers and workmen who liked that class of beer. He objected to the farmer being taxed on barley land to the amount £5 8s. an acre, whilst the bounty-fed sugars and substitutes for barley were practically untaxed. On reply to Mr. Primrose, witness said that the "Welsh ale" he had mentioned and the "harvest beer" produced thirst, but still the people liked it, and would prefer it to excellent beer brewed from malt and hops alone. Asked if the publican adulterated the beer before giving it to the customer, witness said that cases had been detected in London, but it was very seldom done in the country."
Grantham Journal - Saturday 07 November 1896, page 6.
I'd best explain about the Pure Beer movement. After the passing of the 1880 Free Mash Tun Act, there were some who weren't happy about the use of adjuncts. They lobbied for a return tto the restrictions that applied before 1880, when only water, malt, sugar, hops and yeast were allowed.