It’s Not “Infected”


The drummer from a mediocre “punk” band might have an infection, but your beer doesn’t. If there are bacteria growing in your beer, it is contaminated.

When a beer tastes sour, phenolic or otherwise off, you frequently hear brewers describe it as being “infected.” Although we all understand what they are trying to say, a much better term to describe the beer’s condition is “contaminated.”

Infection occurs when a living organism is colonized by disease-causing organisms, such as bacteria, fungi or viruses. For example, a person suffering from a common cold is infected with a rhinovirus. Your body’s immune system is fighting off foreign invaders constantly and typically an intrusion of a foreign organism wouldn’t be termed an infection until the invader “establishes a beachhead” — survives inside you and begins reproducing. (When an organism is invaded by multi-cellular organism, such as a tapeworm or other parasite, the host is usually not described as being infected. Frequently, biologists say the host harbors the parasite.)

When beer has microorganisms in it that lead to sour, phenolic or any of the multitude of bad flavors and aromas rogue microorganisms produce, the beer is contaminated. Although beer is made with parts living organisms — carbohydrates from barley, acids and oils from hops — and fermented by yeast (a living organism), beer is not itself a living organism. The microorganisms are not infecting the beer; neither are they causing the beer to be diseased.

When non-living things harbor bacteria — for example, water — we would say that the water was contaminated by bacteria, not infected with bacteria. Some dictionaries allow for the word “infect” to be used synonymously with “contaminate,” but “contaminate”  is a word that describes the condition exactly, and should be preferred.

Whenever someone hands me a beer and says, “Is this infected?” I say, “I know it’s not infected, by definition, but let me see if it tastes contaminated.”


  1. random reader says:

    Maybe we could use the term transmorgified? I think the odds of getting five gallons of potable water without a contaminating bacteria is very slim. So I would say most homebrews are contaminated. It is only when the bacteria (or other such beast) reach significant numbers to alter the components of the brew is it an issue.

    • Chris Colby says:

      Yes, all beer is contaminated to some degree. There’s a level below which the beer is not effected.

  2. random reader says:

    Odds are. ESL here.

  3. Dan Dewberry says:

    Good points. I should use the proper terminology.

  4. If you clean your equipment properly (err…No sexual references intended) You can choose the “infection of choice”.

  5. A beer that has thinned out and become overcarbonated I understand to be “contaminated” by rogue yeast. So in that case the yeast I chose was joined by its distant relatives and took the beer in a different direction than I intended! If I must drink the result, I’d rather think of it as contaminated rather than “infected”, if you know what I mean!

  6. Static Doge says:

    This article is such aspergers

    • Potato Man says:

      Not at all. It is understandable why the brewing community wouldn’t care about this terminology. But if you have some background in biology/microbiology, you would know that infection and contamination mean very different things (explained in the article).

      I think it is worthwhile to get this right. After all, by brewing, you are essentially doing what microbiologists do in labs–culturing microbes! 🙂


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