How do they know how much alcohol the beverages contains when companies make alcoholic beverages?

Question

For example how do they know/measure that a beer contains 4.5% alcohol?

In: 3

Answer 1

Distillation, and refractometry, and HPLC.

Distillation: Beer and other fermented beverages contain lots of stuff that makes measurement difficult. It’s liquid food, so to speak, so there’s sugars, starches, proteins, all the usual suspects. This makes simple measurements like density inaccurate (like hydrometer readings). Since water and alcohol boil easily, and all the other stuff doesn’t, distillation makes measurement easier. You can test distilled alcohol like vodka directly.

Refractometry: Water and alcohol bend light by different amounts. So, if you shine light through an alcohol-water mixture at an angle, you can measure the alcohol content by how much that angle changes when the light comes out the other side. Sugar solutions also bend light by their own amount, so this only works well with alcohol that’s already been distilled.

HPLC (high-performance liquid chromatography): A separate technique that’s even more accurate than distillation and refractometry, HPLC uses the “stickieness” of molecules to separate them, before measuring how much is there. A small sample is mixed with a solvent. This sample is pushed through a really long tube with more of that same solvent. But that tube is filled with something solid, kinda like sand. The alcohol and water molecules will occasionally stick to the surface of the “sand”, slowing it down. Different chemicals stick more or less, so one thing will come out first, then a delay, then the other thing. Then you just have to figure out how to measure how much not-solvent comes out at any moment. As long as you can figure out which blip of not-solvent is the alcohol, the percentage is as simple as dividing how much came out in that blip by how much total you added. This has the advantage of distinguishing ethanol from all the other alcohols like methanol and 1-propanol that are present in boose in small amounts.

> How do they know how much alcohol the beverages contains when **companies** make alcoholic beverages?

Note that companies will use hydrometers during brewing, but in most countries, that’s not sufficient. The percentage on the label is required to be more accurate than hydrometers can muster.