From the HBD Archive
From: "1107-CD&I/VIRUS DISEASES" <henchal@wrair-emh1.army.mil>
Subject: disinfectants
Date: 1989-07-03 21:42:00 GMT

Recently, there have been several inquiries concerning
sanitation methods. I offer the following insights:

1. Few chemical methods available to the homebrewer can result
in STERILE utensils. Sterile means devoid of any living
organisms. An example of a sterilization method is the use of
steam-based, sterilizers (autoclaves) which do their work at 15
lbs of pressure 212 degrees F for 20 minutes. For the
homebrewer, he can create these conditions only in a pressure
cooker or pressure canner. Most methods are only SANITIZING. To
sanitize means to reduce (or prevent the growth of) the microbial
population to an acceptable level. An example of a sanitizing
method is pasteurization which eliminates target organisms in
food products, but does not sterilize.

2. Methods of sanitation and sterilization should be applied
separately from those meant to merely clean utensils. A rule in
the food industry is to CLEAN first, SANITIZE second. One reason
for the rule is that disinfectants must be able to penetrate the
material you are trying to treat. Soil or residues can actually
protect microbial contaminants from the action of these agents.

3. Bleach (usually 5.25% sodium hypochlorite) is probably one of
the most effective disinfectants available to the homebrewer.
However, most folks use as much as 10 times as required to
disinfect their materials. Chlorine in aqueous solution is
effective in concentrations of 5 to 50 parts per million (ppm).
As a general rule, the bacteriocidal action of chlorine decreases
as the pH increases, and increases as temperature increases.
Chlorine solutions are generally more effective at warm
temperatures, but they are less stable. The hardness of the
water generally has no effect on the bacteriocidal action of
chlorine solutions. A review of the current literature reveals
that as little as 0.2 ppm was effective in 30 seconds against
most vegetative microorganisms. However, some microorganisms are
more resistant. Most spore-forming bacteria (bacillus and
lactobacillus species) required 120 minutes at chlorine
concentrations of 2-3 ppm. Fungi required 30-60 minutes at 100
ppm. The recommendation of the US Public Health Service for the
dairy industry is that hypochlorite solutions of at least 50 ppm
of available chlorine should be used for sanitizing utensils at a
minimum of 1 minute exposure at 75 degrees F.

fluid oz bleach ppm, available
per 5 gallons water chlorine
__________________________ _______________

0.062 (a little more than
1/3 tsp) 5
0.31 (a little less than
2 tsp) 25
0.62 (about 1 and 1/4 tbsp) 50
1.24 (about 2 and 1/2 tbsp) 100

4. Dr. Michael Davis, University of California-Davis recommends
1/4 to 1/2 oz per 5 gallons of water and a contact time of 15-20
minutes. At this concentration, rinsing with water is not
required as long as the utensils are allowed to drip dry.

This is where I think Charlie Papazian misleads people. He
recommends bleach concentrations which are too strong and then
reommends water rinses. Water rinses are ok, but if the
temperature of the water is less than 180 degrees F, you risk re-
contamination of the utensils. (Most water supplies do have some
microbial contaminants. Using the hottest tap water available
usually only results in giving the microbes a sauna bath.)

5. B-Brite is a popular disinfectant, but you MUST rinse the
utensils after treatment.

Some readings:

The Practical Brewer. Edited by Harold M. Broderick, second
editon, 1977, Master Brewers Association of the Americas,
Madison, WI 53705

Disinfection, Sterilization,and Preservation. Edited by S. S.
Block, third editon, 1983, Lea & Febiger, Philadelphia, PA.

"Microbial Controls" by Michael Lewis, In the Best of Beer and
Brewing, pp. 205-226, 1987, Brewer Publications, Association of
Brewers, Boulder, CO 80306.

Those with questions or comments are invited to write to me at my
EMAIL address.

Erik A. Henchal
<Henchal@WRAIR.ARPA>

Oh, by the way Everclear or grain alcohol is an effective disinfectant
also. It is more effective at 70% than undiluted, but it has practically
no effect on microbial spores and less penetrating (because it evaporates
quickly) than aqueous chlorine solutions. I don't recommend that you
use alcohol to disinfect fermentors or utensils, but you can use it to
sanitize work areas effectively.

Last note: Acidic aqueous chlorine solutions are really tough on
stainless steel. In the laboratory, we often disinfect with bleach, but
then rinse thoughly with water, followed by 70% ethanol. In this case,
the bleach is a cleaning agent not the sanitizer.

Henchal

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