The post-rinse sanitizer of choice for many brewers is iodophor. Iodophor sanitizers are iodine based and are extremely effective at destroying beer contaminating organisms such as lactobacillus, mould, pediococcus and wild yeast at 12.5-25 active parts per million (ppm) of titratable iodine.
A problem, however, can occur with iodophor if the amount used is not accurately measured. For a 1.75% titratable iodine concentrate, no more than 30mls per 19liters of water should be used to achieve 25 ppm active. Overusing iodophor serves only to ﬂavour beer and does not offer any additional microbicidal effect. A post-rinse sanitizer which is not iodine based has started gaining acceptance with craft brewers.
Chlorine dioxide (ClO2), like iodophor, is very effective at destroying spore forming organisms at low active parts per million (ppm) levels and does not ﬂavour beer when used properly. Unlike iodophor, however, the amount used is typically not as critical both in terms of microbial reduction and ﬂavouring beer. In other words, you will still get an effective kill at an active level of 50-100 ppm ClO2 while maintaining a minimal or non-existent ﬂavour proﬁle.
Mention the words “chlorine” and “sanitizing” in the same breath around most brewers and their response is, normally, “It will ﬂavour my beer.” (This usually comes from the same person who taints his / her brew with iodophor). In the case of sodium hypochlorite bleach, they are correct. As little as 1-2 ppm active hypochlorite is detectable in drinking water.
Triple rinsing is necessary to remove bleach from brewing equipment and bottles so as not to ﬂavour the beer with chlorine. Therefore, post-rinse sanitizing equipment and bottles is not recommended with hypochlorite bleach. Conversely, chlorine dioxide is ideal for sanitizing after the cleaner has been rinsed. Chlorine dioxide removes phenolic tastes and odours from water and does not form trihalomethanes or chlorophenols.
This is very important to the brewer because these compounds are extremely detrimental to beer, not to mention the toxicity to humans or the environment. Chlorine dioxide is also used to remove cyanides, sulphides, aldehydes and mercaptans from water. These compounds are unfavourable for beer, too. That’s great, you say, but what is chlorine dioxide? Chlorine dioxide can be used to sanitize all brewing equipment that comes in contact with beer, from the heat exchanger to fermenters to the keg or bottle and everything in between.
For heat exchangers, open fermenters, secondary fermenters, Zuni’s, serving/bright tanks and kegs, a 50-100 active ppm solution of chlorine dioxide is recommended for post-rinse sanitizing. The solution is normally either pumped through spray balls (like CIP), or in the case of open fermenters, sprayed with a pump-up sprayer just before the beer is pumped over to the fermenter being sanitized.
Again, there is no danger of ﬂavouring beer if the proper amount of sanitizer is used. The spore-formers such as yeast and mould cannot develop immunity to the oxidation of the chlorine dioxide, which makes it an ideal sanitizer for the brewer.
The “tried and true” method of washing yeast utilizes phosphoric acid (H3PO4) to acidify the yeast slurry to around pH 2, where it is held for a given amount of time, ranging from two hours to overnight. In theory, undesirable organisms are destroyed by the low pH and trub is removed from the yeast. The healthy yeast remains suspended and is used for pitching, while dead cells and trub collect at the bottom of the washing vessel.
However, there are several problems with acid-washing. It reduces the populations of most wort-spoiling bacteria, but is less successful with beer-spoilers such as lactic-acid bacteria, and is generally not effective on wild yeasts and moulds. Further, the low pH tends to stress the yeast, and for this reason most breweries wash with acid only rarely. Recently, a few breweries have begun using an acid-free wash that allows them to wash their yeast on a regular basis.
Chlorine dioxide (ClO2) has been used for decades to disinfect drinking water. In this scenario, chlorine dioxide kills by penetrating the hydrophobic region of the bacterial membrane and oxidizing it. Chlorine dioxide reacts with sulphur-containing amino acids, which form cell membranes. The proteins get destroyed, the membrane ruptures and the organism dies.
Chlorine dioxide is relatively new to the brewing industry. It is gaining acceptance as a post-rinse sanitizer, but is not widely-recognized as a yeast-washing agent. Given what is known about it, however, it makes sense that it might be an effective, economical and safe alternative to phosphoric acid.
Chlorine dioxide has (in theory) over 2.5 times more oxidation capacity than elemental chlorine but does not have a chlorine-like ﬂavour proﬁle. Chlorine dioxide does not form trihalomethanes, as does sodium hypochlorite (household bleach) and iodophors, and breaks down to innocuous compounds, namely table salt and water.