Steel fermentation vessels are seen at the Guinness brewery in Dublin in 2014. The brewery is the world’s largest maker of stout beer, and the largest brewing tanks can hold up to 750,000 pints each. (Shawn Pogatchnik/AP)

To the delight of vegans everywhere, Irish brewery Guinness revealed this week that it will stop using fish guts to make its famous dark stout.

Who knew there were fish guts in beer in the first place?

Let's take a step back. First, it’s true that the production of Guinness involves the harming of some critters. This is not unusual; many beers and wines are made using animal products. These ingredients aren’t added to flavor the beverage, but to help purify it. Only trace amounts remain in the final drink.

Nonetheless, Guinness has been trying to become more vegan-friendly. By the end of next year, Guinness’s main plant in Dublin plans to have an alternative system for filtering beer, a spokesperson said in an e-mail.

Brewing is the process of using yeast to turn the sugars and carbs in grains and fruit into alcohol. After the yeast has done its job, the particles die and fall to the bottom of the tank and get filtered out (or not). Brewers often use animal or vegetable products to clump up the yeast so it settles faster and leaves the beer or wine as clear as possible.

A favorite ingredient among British brewers is isinglass, a clear gooey substance that is dissolved out of the bladders that fish use to stay afloat. Isinglass is mostly just collagen, a crucial — and abundant — animal protein perhaps best known for plumping celebrity faces. Fish swim bladders are a traditional source of very pure collagen. Monks used isinglass in the Middle Ages as a glue to repair parchment and apply decorative gold leaf to their manuscripts.

Isinglass has played a role in clarifying beer for hundreds of years. By the mid-18th century, it was ubiquitous in England, according to Cambridge professor Peter Mathias’s history of the beer industry. It has now become a tradition for British brewers to continue using isinglass — you won’t tend to find this substance in American or German beers.

But even beers dosed with isinglass contain little of it; most of the fish protein gets removed along with the yeast, which is the point of the whole process. A 2007 study found that there remain at most a few milligrams per liter, and typically far less than that in commercially bottled beers.

There is some concern that isinglass may trigger allergies for people who are sensitive to fish. But a spokesperson for Guinness cited vegetarians as a major reason that the brewery wants to become isinglass-free. Animal-conscious consumers are a growing force in the marketplace — there are now databases for vegans to determine which beers have animal ingredients, and Guinness itself has been petitioned to stop using isinglass.

That's not all...

For those who would avoid anything that came from an animal, the purging process is never-ending. Irish beer is far from the only thing in our lives that is surprisingly not vegan.

Take condoms, for instance. They’re made out of latex, which is often treated with casein, a milk protein. This distresses some vegans. (The presence of casein in latex gloves has also led to confusion when people are tested for allergies.)

Beef fat, or tallow, shows up a lot in our everyday lives. It’s used in soaps and crayons and candles. United Airlines is exploring using tallow to fuel its jetliners, so in the near future, you could be flying on a plane burning animal fat.

Joints and bones and skin are rich in collagen, which is boiled to make gelatin — the main ingredient in jellos, but also most gummy snacks and some jams. Gelatin also shows up in gel-style pills.

The list goes on and on. Crushed bones are used in fertilizer. Animal fats are turned into glycerin, a lubricant that shows up in lotions, toothpaste, shampoo and the liquid used in bubble machines.

There exist vegetable alternatives to most of these ingredients, but if your gummy snacks don’t say they’re made from vegan gelatin, you’re probably chewing on something that was recently mooing or oinking. These animal products tend to be much cheaper because they’re left over from industrial meat operations.

What to do about it all?

Perhaps it's a myth that Native Americans used the whole bison — but modern farming really does find a use for every part of the animal. This is a fact to be celebrated. It's a gesture of respect that nothing gets wasted.

Even the animal rights activists at People for the Ethical Treatment of Animals urge people not to take notions of vegan purity too far. Focus on the animals, they say:

Being vegan is about helping animals, not maintaining personal purity. Boycotting products that may contain trace amounts of animal products can actually be harmful to animals in the long run. For example, by refusing to eat a veggie burger from a restaurant because the bun may contain traces of milk or eggs, you are discouraging that restaurant from offering vegan options because it … seems too difficult a task.

It is futile to try to live a modern life that is divested from these ingredients. Animal byproducts are ubiquitous because meat production is ubiquitous.

For those who want to make the world a better place for animals, not eating meat is a great place to start. But the economics of boycotting animal byproducts don't make sense. Nobody raises pigs just to boil their bones down. Nobody farms cows just to run their fat through airplane jet turbines. And nobody harvests cod just to collect bladders for brewers of traditional-style beers.

Guinness has not said how much it will cost to refit its flagship brewery, but the investment could be significant. "It’s a complex project and will take many months to install and test before it goes live," the spokesperson said.

What's unclear is how much the project will benefit animal conservation. Some of the highest-quality isinglass is said to come from sturgeon, which are harvested mostly for their meat and caviar. That industry will continue whether or not Guinness successfully renounces fish guts.