How was beer production affected by the war during WW2?

Also, in the United States grain rationing led to the use of further adjuncts in the beer like rice and corn. This led to the American style of "light" beer, introduced by Budweiser.

The "only in Canada" answer...odds are if you were drinking a regular beer like those of pre-war times, it came from Canada.

WWI saw the return of victorious soldiers to their home nation which had gone dry!

At the end of the war, thousands of Canadians returned victoriously home. After four years they had succeeded in defeating the forces of authoritarianism, but having put their lives on the line, many of these same veterans were horrified to find that the country they had fought for was in the grips of prohibition. “Having resisted the tyranny of Wilhelm,” stated the Great War Veterans Association (GWVA)—the forerunner of The Royal Canadian Legion—“we do not propose to submit to the meanest of all tyrannies, the tyranny of petticoat government and its embrace of the dry regime.” In time, Canada’s First World War veterans and their supporters would win the right to drink beer and, in the process, create a culture of moderation that we now consider very much Canadian.

(This is actually from the story of Molson which became one of the prominent brewers in Canada. https://legionmagazine.com/en/2010/03/for-beer-and-country/ 'For Beer and Country!')

During WWII, the Ontario Brewers took up a public relations battle to ensure the prohibition of WWI would not return.

IN THE SUMMER of 1941, Matthew H. Halton, a war correspondent, arrived in Solum, an Egyptian village near the Mediterranean Sea, just east of the border with Libya. The British army there was under heavy attack by General Erwin Rommel – the fabled “Desert Fox.” As the shells of the German Afrika Korps rained down on Solum, Halton fearlessly recorded the fighting and dying in the searing sands of North Africa. The fact that “one brigade with a few guns” ultimately held off the German assault left Halton “shaking with pride.” When the fighting was done, a charming young British lieutenant approached Halton and offered him a drink. But Halton knew that it was an unforgivable sin in the desert to accept water or other drinks from people, and as a result he replied “No thanks.” The lieutenant, however, insisted. “Save your protest and drink the beer,” he commanded. “It’s Canadian.”

This story, along with several others, were portrayed in canadian media as

Halton’s article and others like it were designed to highlight the brewers’ contribution to the war effort by demonstrating that beer was necessary for promoting camaraderie and good health while maintaining civilian morale at home.

Defending the Right to Supply Beer to the Troops Overseas Much of the early activity of the PRCOB was dedicated to defending the brewers’ right to supply beer to the troops overseas. In January 1941, Canadian brewers had been asked to supply the British Navy, Army, and Air Force Institute, which operated the wet canteens for Commonwealth forces in all fighting theatres. Canadian brewers were already distributing beer to canteens on airfields and army bases across the nation, where there was a preference for bottled beer.41 Close to a million men and women had enlisted in the Canadian military, and to this group was added the young men from other countries who were in Canada to receive their flying training under the British Commonwealth Air Training Plan. Despite the growing demand for beer on the home front, Canadian brewers responded to the British order. Within weeks, 400,000 dozen quarts were shipped in the first allotment for the British government.

Some Canadians took supplying beer to Canadian soldiers and their allies as a patriotic duty.

https://labattheritage.lib.uwo.ca/closer-look/supporting-canadas-troops

Beer played a fortifying role again during World War II (1939-1945). John S. Labatt took pride in the fact that his brewery was supplying some “cold comfort” to the fighting men in the hot theatres of Europe, North Africa and East Asia. Soldiers like Warrant Officer B.A. Proulx were grateful to Labatt for contributing to the war effort.

After his escape from Hong Kong, Proulx was astonished to find that the drys were criticizing Labatt for supplying Canadian soldiers with beer. “It never occurred to us, while we were under fire by the Japanese,” Proulx protested, “that our people at home were waging a battle to prevent us from having something that we not only wanted but also sorely needed.”

During the Second World War, more than 20,000,000 gallons of Canadian beer was shipped to the troops overseas. Canadian beer helped those on the front lines cope with the toughest conditions. Beer calmed the nerves, relaxed the body, and uplifted the soul. It built bonds between the fighting men and helped carry the Allied nations through the war and on to victory.

A funny side note, Canada's Prime Minister issued the 'Wartime Alcohol Beverage Order' which restricted domestic beer consumption during the war. This led to a nearly immediate black market and protest:

No other shortage brought more of an uproar during the war than the lack of beer. Canadians proved to be willing to put up with a virtual famine of other items. But the inability to get a glass of beer after finishing a day’s work was something that wartime workers and military men could not stomach. Their protests were many and often. In Vancouver, for example, angry shipyard workers threatened to boycott the sale of victory bonds if they did not get more of their favorite beverage. ”No Beer – No Bonds” was their battle cry. Across the nation, wartime workers and veterans signed petitions to register their disapproval of the beer restrictions. Although the medium took many forms, the message was always the same: “We want more beer.”

The extents they went to get beer to soldiers resulted in some amusing tales. http://www.veterans.gc.ca/eng/remembrance/history/second-world-war/flyers-remembrance#brun

On June 13, 1944, (D-Day plus seven) number 412 (Falcon) Squadron, along with the others comprising 126 Wing gathered for a briefing by W/C Keith Hodson at our Tangmere base.

The Wingco singled me out to arrange delivery of a sizable shipment of beer to our new airstrip being completed at Beny-sur- Mer.

The instructions went something like this – "Get a couple other pilots and arrange with the Officers Mess to steam out the jet tanks and load them up with beer. When we get over the beachhead drop out of formation and land on the strip. We're told the Nazis are fouling the drinking water so it will be appreciated."

"There's no trouble finding the strip, the Battleship Rodney is firing salvoes on Caen and it's immediately below. We'll be flying over at 13,000 so the beer will be cold enough when you arrive."

...

In reflection it now seems like an appropriate Air Force gesture for which the erks (infantrymen) would be most appreciative.

...

Wheels down and in we go, three Spits with 90 gallon jet tanks fully loaded with cool beer.

They were told to get out fast...

"Look," he said "can you see that church steeple at the far end of the strip? Well it's loaded with German snipers and we've been all day trying to clear them out so you better drop your tanks and bugger off before it's too late."

Beer drop under sniper fire? worth it!

http://www.oldbeers.com <- contacting the owners of the Pretty Things Brewery might be able to help. They have a project brewing old beer recipes.

Basing my answer off a single source (the 1945 beer recipe used by Pretty Things) it appears that there was limited variety in brewing materials as well as a lower alcohol content. It makes sense, as you can't limit the amount of beer, but you can use fewer ingredients to make the beer while rationing.