There’s a time for tongue-puckering lambics and Berliner Weisses, but most beer drinkers want something a little more balanced for day-to-day sipping. Thanks to the pH scale that Tuesday’s Google Doodle honoree S.P.L. Sørensen invented in 1909 at Carlsberg Brewery in Copenhagen, we can now measure the level of acidity in a beer — as well as any other substance.

Technically, pH refers to “potential” or “power” of hydrogen (the exact term is still disputed). What Sørensen, a Danish chemist, actually invented was a way to measure the level of hydrogen ions in a substance. Very broadly speaking, hydrogen ions are associated with higher acidity (a pH of 1 is as acidic as you can get). Hydroxide ions are linked to basicity (pH 14 is peak #basic), which is the opposite of acidity. When they’re in solution together in equal amounts, the two cancel each other out, creating a true neutral substance — pure water, with a pH of 7.

This ability to measure the acid-base balance revolutionized the way we heal the sick, grow our food, treat wastewater, and, yes, drink beer. Sørensen, we raise our delicately balanced, just-tart-enough glasses to you.

pH scale
The pH scale measures the level of hydrogen ions (acidic) relative to hydroxide ions (basic) in any substance.

Medicine

Blood Cells Feel free to use this image by giving credits to SciTechTrend.com
Regulating blood pH is key to preventing acidosis or alkalosis.

The fact that the human body has its own acidity-regulating system, keeping the pH of blood around pH 7.365 (slightly basic), is proof enough that it’s important for us to be able to track it. Most of the body’s enzymes and proteins evolved to work optimally at that pH, so things can go very badly when the blood becomes too acidic or too basic. Acidosis can cause fatigue, shortness of breath, and confusion; alkalosis is linked to similar symptoms as well as muscle twitching and spasms.

There are a number of things that can throw off the blood’s acid-base balance: Obesity, respiratory diseases, and sedative overuse can cause hyperacidity, while lung and liver disease, high altitude, and lack of oxygen can cause alkalosis. The ability to easily track the pH of the blood — now all it takes is a simple pH strip! — is crucial to treating these conditions as they arise.

Agriculture

Maizal
Most crops, like corn, grow in slightly acidic soil.

Just like human blood, soil has a delicate acid-base balance. Not all soils have the same pH, though, and different plants have different pH preferences. For the most part, crops grow best in slightly acidic conditions: staple crops like barley, corn, cotton, peanuts, rice, soybeans, and wheat prefer soil with a pH of about 5.5 to 6.5, whereas outliers like blueberries and Irish potatoes prefer even more acidic soils, and alfalfa and sugar beets prefer soils closer to a neutral pH.

Fortunately, scientists have figured out what to add or remove from soil to make it more hospitable for certain crops. When you’re a farmer trying to make a living, or a government trying to grow a nation’s dinner on mediocre soil, you better believe that Sorensen’s pH scale is a game changer.

Water Treatment

Blackmoorfoot Reservoir
Reservoirs are rarely full of purely neutral water, so pH needs to be adjusted into a drinkable range.

Pure H2O is a soup of hydrogen and oxygen atoms, which exist as acidity-giving hydrogen ions (H+) and basic-making hydroxide molecules (OH-). Swirl them all together and they cancel each other out, giving pure water a truly neutral pH of 7.

But pure water rarely occurs naturally, as minerals, metals, and other substances in our reservoirs leach into the water we drink. According to the United States Environmental Protection Agency, pH is a secondary concern — slight acidity or basicity is considered largely an “aesthetic” issue — but still recommends that drinking water stays within a pH range of 6.5-8.5. Acidic or basic chemicals can be added to wastewater to not only adjust its acidity but force certain heavy metals and toxic elements to precipitate and filter out. In particular, making water more basic releases more hydroxide ions, which have a tendency to hook up with metal ions; when they do so, they fall out of the water as solids, making it easier to filter them out.

Drinking Beer

Enter The Malt
To convert the sugars and starch from grain into alcohol, enzymes require a very specific pH range.

Beer, like the human body, relies on living enzymes for its existence. Before it becomes a tasty alcoholic elixir, beer is a pile of mashed-up malt grains leaking out sugars. To turn those sugars into alcohol, you need yeast and all its enzymes, which — just like human enzymes — are happiest at a very specific pH range.

In his seminal work, Sorensen showed how to keep tabs on pH so that beer’s starch-converting enzymes, alpha amylase and beta amylase, stay satisfied. Without the ability to keep tabs on pH, brewers would be unable to ensure that all the starch and sugar in the beer is efficiently converted to alcohol — which would be a beer drinker’s nightmare, indeed.