In commercial brewing operations, there are several definitions of cleanliness. They are: physical cleanliness, which means the surface is visually clean to a satisfactory standard; chemical cleanliness, where the surface is clean to a standard where any contact by the product with the cleaned surface suffers no contamination; and, finally, microbiological cleanliness, where the surface is cleaned to a level at which no physical or microbiological contamination is present.
Standards of cleaning for each part of the process
Brewing area: The first place a difference can be made to overall cleanliness is in the planning stages of your home brewery. Ensure that your working area is clean and remove extraneous items from the work area. Thoroughly clean the working area. When it comes to choosing equipment, consider how it will be cleaned and sanitized.
Mill: Flour and particulate matter from the milling process can accumulate around the mill and surrounding area and cause a problem with bacterial and fungal growth. Malt dust is an excellent vector for beer spoilage microorganisms. Cleaning manually with brushes and a vacuum cleaner, or blowing down with compressed air is sufficient. Malt on the floor can lead to rodent problems with the associated sanitation risks. The buckets you use to store your grain will see a build-up of dust and particulate matter and mold will grow quickly. Regularly empty and hose out the inside to remove the dust.
Mashing-lauter tun: The mash tun can get build-ups of particulate matter. This includes starch, sugar, protein, hard water scale and tannins. This should be chemically cleaned, either manually by scrubbing with an abrasive pad and hot water, or by soaking in an appropriate detergent. Pay particular attention to the area under the separation screens and the screens themselves. Particles of malt lodged in the screens can produce an excellent source of wort spoiling bacteria.
Boiling: The kettle gets build-ups of particulate matter, including starch, sugar (often caramelized), protein, tannin, protein/tannin complexes and scale. It must be chemically cleaned, either manually by scrubbing with an abrasive pad and hot water or by soaking in an appropriate detergent. The commonly available green kitchen scrubber pads should suffice, although beware of those that come already impregnated with a detergent. Metal scourers and wire wool are a bad idea since they may embed particles of steel in your stainless pot and cause it to rust. If the pad is too course, however, it can scratch the metal surface and scratched surfaces are harder to clean. I like Teflon abrasives for my stainless cookware since it does not scratch the surface.
Wort cooling: The heat exchanger, often a simple copper coil, can become fouled with particulate matter (hops), trub, protein and hard water scale. It must be microbiologically clean, since bacteria can readily infect cold wort. This can only be achieved with soaking in an appropriate detergent followed by disinfection, and maybe even periodic dismantling and manual cleaning.
Fermentation and conditioning: Fermenters and conditioning tanks must be cleaned of yeast, protein, trub, tannins, sugar and hard water scale. They must be microbiologically clean and this is achieved by manual methods, often a combination of different chemical methods followed by a disinfecting rinse. The same goes for kegs and bottles in which the beer will be packaged.
Filtration: Filters can become fouled with yeast, trub, protein and scale and must be kept microbiologically clean. This can only be achieved with a detergent soak or flush, followed by a disinfectant rinse.
Beer stone is the grayish white layer that gradually builds up on the inside of your brewing system. Organic compounds in the wort and beer, such as proteins and polypeptides, bind with compounds derived from the brewing water, mainly calcium and magnesium oxalates. The oxalate compounds form when the carbonate compounds of these metal ions react with organic acids in the wort to form a white crystalline precipitate. This complex adheres to the stainless steel surface of the tank and builds up over time. It can only be removed by breaking down and solubilizing the protein, then dissolving the mineral scale. This requires a dual treatment of an alkaline detergent that dissolves the organic component and an acid cleaner that dissolves the inorganic compounds.
Chemical detergents fall into two categories, alkalis (bases) and acids.
Caustic soda (sodium hydroxide): Commercial brewers use sodium hydroxide and it is very effective at cleaning brewery equipment. Unfortunately, in hard water it can form solid precipitates that reduce its effectiveness. This can be overcome by using softened water or by the careful addition of sequestrants, such as EDTA. These chemicals bind the calcium, which causes water hardness, and prevents it from reacting with the caustic. Commercial brewery cleaners contain sequestrants and many of these are now becoming more available for home brewer use. Powdered Brewery Wash (PBW) is a product that is now being used by some homebrewers. It relies on the use of sodium metasilicate, which can clean like caustic but not as aggressively, mixed with EDTA as a sequestrant and various surfactants. Caustic soda will also react with carbon dioxide to form a solid precipitate. Sodium hydroxide in solution combines with carbon dioxide gas to form solid sodium carbonate. A fermenter, aging tank or keg needs to be purged of the gas before being cleaned with caustic. This reaction not only reduces the effectiveness of the sodium hydroxide as a cleaner, but the exchange of a gas for a solid inside a closed tank can produce a tank that looks like a crushed beer can!
Acids: Caustic's tendency to absorb carbon dioxide can sometimes cause problems, so acids can be considered as an alternative. Their ability to dissolve inorganic mineral deposits is vital in cleaning a surface completely. In a commercial operation, phosphoric acid is the most commonly used acid although it must be blended with surfactants. If nitric acid is added, the mixture is more aggressive. Other acids may be used — i.e. sulphuric and hydrochloric — but both will attack stainless steel in their concentrated form. When using any acid, corrosion is an issue and so care must be taken with acids anywhere on your brewing equipment where mild or stainless steel is present. This also applies to concrete floors.
Most brewery tanks will require a combination of both types of treatments to clean the surface effectively. The order in which they are used is up to the user but a caustic soak followed by an acid soak is the most common method.
Disinfectants are used in manual and soaking methods as the final step in obtaining a microbiologically clean surface. They fall into two categories, defined by the way in which they kill bacteria. These disinfectants can be either oxidizing (or oxygen releasing), or non-oxidizing types.
A disinfectant used on brewing equipment should be compatible with other chemicals in use and the material the equipment is made from. It should be effective even when used in hard water and able to deal with some soil being present. It should be safe to use for humans, not taint the beer or harm the foam. It should destroy a broad range of micro-organisms, including bacteria, yeast, moulds, fungus and maybe even viruses. It should be affordable and have a low environmental impact.
Oxidizing disinfectants: A class of chemical elements known as halogens are renowned for their ability to take part in chemical reactions that result in another compounds becoming oxidized. Cell walls of bacteria, or any cell for that matter, are succeptable to extreme damage from these elements. Halogens include chlorine, iodine, and bromine — although only the first two are likely to be encountered in brewery equipment sanitation.
Active chlorine is used in two forms, either as a compound containing hypochlorite ions as a liquid (bleach) or as a powder (chlorinated trisodium phosphate or TSP). In solution, these compounds produce hypo-chlorous acid or hypochlorite ions, depending on the pH. Bleach is most stable when stored inactive at pH 12 as it has been mixed with caustic. But, when diluted in water, the buffering action disappears and the pH drops to 7–9. Bleach is also very corrosive to stainless when the pH drops below about 10. Care must be taken with this chemical since, at pH 5, deadly chlorine gas can be formed — so never mix bleach with acids.
Its action on microorganisms is the oxidation of cell wall proteins and the destruction of cellular enzymes along with DNA and RNA. Its action is reduced in the presence of heavy soils, since it will oxidize all proteins. Inefficient rinsing of the detergent can leave residual chlorine, which can react with phenols in beer producing medicinal off flavors.
Iodine in not very soluble in water and in its gas form is very toxic, so it is difficult to handle. However, when mixed with surfactants and dissolved in acid, iodine can be used effectively. These compounds, known as iodophors, are commonly used in small breweries as final rinse and soak bath disinfectants and are readily available to home brewers. Iodine is substantially lost from the solution at over 104 °F (40 ° C), so they must be used cold. The activity depends on the oxidative power of the iodine molecule and its action is similar to chlorine. The optimum pH for activity is 5. Another advantage is that they are yellow or brown in color when enough iodine is present, but turn colorless once the active ingredient is used up. A disadvantage is that the solution will stain and taint hoses and plastic parts.
Recently there has been new interest in chlorine dioxide sanitizers, such as OxineTM. They are powerful oxidizing agents relying on the instability of the chlorite ion and its strong tendency to pick up an electron and become chlorine dioxide.
OxineTM is stable in its inactive form but, once activated by lowering the pH (addition of acid), it becomes a powerful disinfectant. It can then be diluted and used safely in the brewery. Its action is entirely oxidative, attacking proteins at their weakest point, denaturing them by breaking the sulfur bonds forming the double helix. It does not form any chlorine organic compounds, especially chloro-phenols so it less of an environmental concern, and it's not corrosive, either.
Peracetic acid is a molecule of acetic acid with an additional oxygen atom attached. It is extremely unstable and readily donates an oxygen ion, which can rapidly oxidize cell proteins and DNA and RNA. It can penetrate cells and destroy the proteins and enzymes of the entire cell. It is effective against bacteria (including spore formers), yeast and even viruses. In its commercial form, it is stabilized with hydrogen peroxide and its name becomes peroxyacetic acid, which becomes very active upon dilution. The mixture will break down to acetic acid and water after it is exhausted
It is too dangerous to apply manually, and its active life is not long enough for prolonged soaking but in a commercial brewery it makes a very fine tank rinse.
Hydrogen peroxide is very unstable, so is not recommended for manual or soaking use. It is bactericidal and fungicidal, but some bacteria produce an enzyme that can destroy its activity.
Most sanitizers are designed to be sprayed onto a surface and left there to become safe and harmless. If you are using any of these sanitizers, be aware that they are equally capable of oxidizing beer components as they are in killing bacteria. So never exceed the recommended concentrations.
These are usually complex compounds that are electron donors such as quaternary ammonia compounds (or QATs). The most common one is Lysol. Non-oxidizing disinfectants are affective against bacteria, yeast and molds, but are never used on brewing equipment anymore because their residue can affect head retention in beer. Certainly use them to clean and sanitize the working area though.
Steam and hot water A lot of brewers use hot water (>180 °F/82 °C) or steam to sterilize. As a sanitizer it is extremely effective as nothing lives when used properly, although the heat can cause soil residues from insufficient pre-cleaning to bake on to a surface. Another problem is that cooling tanks take in dirty air and can be recontaminated.
Steve Parkes writes the Homebrew Science column in each issue of BYO.