Antimicrobial properties of ethanol

[Fenster]

One of the topics I have seen people muse about on this board has been the level of ethanol required to inhibit growth of “nasties” in our beer.

It has been said many times (correctly) that the huge numbers of yeast in fermenting beer out-compete the other microbes in solution, however the question still arises from time to time: How much ethanol is necessary by itself to be antimicrobial?

After lugging out my old microbiology text I have uncovered the following:

1. There is a big difference between inhibiting growth of nasties and killing them outright. Assuming that you have relatively aseptic conditions I think that inhibition is all we need to achieve.
2. Inhibition can occur at ethanol levels as low as 10%. Even the hardiest yeast cannot grow in alcohol exceeding around 15%, which is why you don’t see wine with higher ABV. Most wild yeasts can only tolerate around 4% alcohol before they stop fermenting.
3. According to my text (Brock Biology of Microorganisms 9th edition) alcohol levels must be at 60-85% in order to be truly antiseptic. This number is surprising to me. Prior to reading this I had assumed that a bottle of spirits would be a sufficient antiseptic.

I hope this helps someone, now back to your regularly scheduled program.

 

[Beerrific]

Yup, good old 70% ethanol, that is what we use around the lab to spray our hands and bottles before putting them in the biosafety cabinet. It does not kill bacteria spores however.

 

[Yuri_Rage]

You're forgetting that hops also have a preservative nature. The combination of ethanol, hops, and yeast "competition" makes it unlikely for "nasties" to invade fermented beer.

 

[mew]

You're forgetting that hops also have a preservative nature. The combination of ethanol, hops, and yeast "competition" makes it unlikely for "nasties" to invade fermented beer.

Don't forget acidity.

 

[mrfocus]

Double acidity actually.

Acidity from the wort being acid and also acid from a small amount of the dissolved CO2 becoming bicarbonate (HCO3) which will even further acidify the solution.

 

[e lo]

+1 on 70% EtOH.

Beerrific, what kind of lab do you work in?

 

[fastricky]

Is 70% Ethanol a better sanitizer than say Star San?

 

[Edcculus]

Is 70% Ethanol a better sanitizer than say Star San?

Probably better for small items or if you culture yeast, but not as a general purpose no rinse sanitizer.

 

[fastricky]

Well, it was with the intention of using 70% Ethanol over StarSan to sanitize equipment used in harvesting yeast... so, is it a better option in that case?

 

[Edcculus]

Well, it was with the intention of using 70% Ethanol over StarSan to sanitize equipment used in harvesting yeast... so, is it a better option in that case?

Hmm, thats a really good question. Maybe someone who work in a lab would be able to answer better than I can though.