The Importance of Cleaning and Sanitation in Homebrewing

Abstract

The expansion of homebrewing among hobbyists and beer lovers has enabled the availability of fabulous and non-conventional flavors to a broader public. However, homebrewing conditions are not standardized and greatly depend on the meticulosity of the homebrewer. To ensure minimum hygienic conditions, homebrewers need to employ more effort than the standardized brewing industry. Cleaning and sanitation ask for a meticulous and thorough, almost perfect cleaning and sanitation pattern in order to ensure healthy fermentation and safe beer. The implementation of cleaning and sanitation methods can greatly prolong the lifespan of kegged or bottled beer and accent the excellent aromas and taste of homebrewed beer. Since there is a lack of scientific literature concerning this aspect of brewing, this paper is conceptualized as a review that covers all the major concerning/hazardous points in homebrewing and summarizes potential actions to maximize cleaning and sanitation efficiency in the homebrewing process.

1. Introduction

Since the beginning of time, people have enjoyed brewing. The first brews were perhaps not similar to the contemporary beers, but they also connected people and made them joyful. Brewing purports alcohol fermentation and this usually means that this is a naturally protected process. This means that contamination from unwanted microorganisms would not impair or halt the fermentation due to the alcohol content in the brew [1,2].

According to Corran [3], brewing originated from the Middle East and has been known to mankind since 8000 B.C. The Mesopotamians were devoted brewers, as it is known that they left about 40% of cereal crops for brewing. From the Middle East, brewing arose and spread to Northern Europe and beyond. The Roman historians Tacitus and Pliny described the use of foaming agent in brewing, later known as yeast [4]. It was in 1680 that Leeuwenhoek described a yeast cell [5] and further examination by Gay-Lussac and Pasteur contributed to understanding the microbiological and biochemical profile of alcohol fermentation.

To emphasize the size of homebrewing movement, it is important to report that there are over 1900 homebrewer’s clubs related to American Homebrewing Association, and numerous similar associations and clubs in Europe and the rest of the world [6,7]. However, the positive aspects of yeasts in alcoholic fermentation can be impaired by different microbial contaminators, which are thoroughly defined and classified in modern science. Brewing, especially homebrewing, involves microorganisms (yeast and bacteria) in order to produce beer; thus, it is immensely important to ensure aseptic conditions prior to, during, and after production. Since homebrewing does not undergo any of the food safety management systems and is carried out without any external control, it is extremely important for the homebrewer to maintain the equipment and environment clean and sanitized. Another important point in homebrewing is the packaging and storage of beer, which also has to be carried out under aseptic conditions, especially since many unit operations (e.g., filtration, pasteurization) usually performed in the brewing industry are omitted in homebrewing. These unit operations are performed in order to stabilize the beer (not only microbial-wise) and prolong its storage time [2,8,9].

In order to better understand the matter of this review, certain terms should be addressed and defined. Cleaning is the process of physical or chemical removal of visible dirt or residues from the brewing equipment and surfaces. This is usually followed by disinfection, which helps remove spoilage microorganisms that could impair fermentation process and end up in beer [8]. Sanitation is a process wherein the aim is to reduce the ability of microorganisms to proliferate; it is commonly performed after the proper cleaning methods have already been conducted [8]. These two methods are usually carried out in homebrewing conditions.

This review aims to point out the importance of hygiene measures in homebrewing, to identify the main hazards along the beer production chain, to suggest actions to avoid contamination, and to ensure that the homebrewing process and beer are both safe and healthy.

2. Common Microorganisms in Brewing

Beer is thought to be a fairly safe product due to its compounds: hop compounds, alcohol, and CO₂ and SO₂ concentrations. Low oxygen content and low pH contribute to beer being resistant to microbial contamination [2]. However, smaller-scale brewing, such as homebrewing, portrays different and unknown conditions [9]. Brewing in the industry is a closed process and has minimal potential for contamination. On the other hand, homebrewing is often carried out in yards, basements, sheds, or even in bathrooms. The addition of different fruits, herbs, and spices increases the risk of microbial contamination [9,10]. This section describes the common and general microorganisms in malting and brewing and sources of contamination.

2.1. Microorganisms in Malt

Microorganisms in malt are commonly related to barley’s microbiological image, which originates from field and storage. Malting conditions purport high moisture in the substrate grain (≈45%) and air (>85%) and somewhat lower temperatures (14–18 °C). Most infamous microorganisms that cause problems in malting are molds, especially belonging to the genus Fusarium [11]. Even though finished malt is not usually known for microbial contamination, due to low water content (<5%), some species can be found on it. Certain lactic acid bacteria can be found in finished malt such as Lactobacillus leishmanii, Pediococcus acidilactici, Lactobacillus delbrueckii subsp. delbruecki, and Lactobacillus delbrueckii subsp. lactis. Other bacterial species involve Erwinia herbicola, Pseudomonas spp., with micrococci and Bacillus spp. Yeast of genera Sporobolomyces and Rhodotorula are found in many counts. Fungi such as Aureobasidium pullulans and Geotrichum candidum, and filamentous yeasts in the genus Trichosporon, Eurotium (Aspergillus) amstelodami, Rhizopus spp., Penicillium spp., Alternaria alternata, various Fusarium spp., and Cochliobolus sativus have also been detected [11]. Fungal contamination usually results with mycotoxin contamination, which can have serious consequences on human health. However, today’s efforts are pointed toward a reduction in mycotoxins in crops in general, and malting technology aims to reduce the occurrence of fungal contamination as well.

Homebrewers usually do not have appliances that can maintain ideal or somewhat ideal conditions for storing malt. This would usually mean that malt is kept in different plastic containers at room temperature. However, malt should be kept in refrigerated space at lower temperatures (<15 °C) to reduce the development of different pests, including fungal proliferation. Plastic containers serve the purpose of reduced oxygen and moisture intake to the grain; still, room temperature and a moist environment can affect and trigger enzymatic degradation, insect occurrence, and microbial infection [12]. This can be avoided by using appropriate environmental conditions (regulation of temperature and humidity), and by implementing sanitation measures [13].

2.2. Microorganisms in the Brewing Process

2.2.1. Lactic Acid Bacteria

Lactic acid bacteria are G+ bacteria and can metabolize carbohydrates via two pathways: the heterofermentative and homofermentative path. In a homofermentative pathway, glycolysis occurs, and only one metabolite emerges as a result–lactate. A heterofermentative pathway results in various end-metabolites (lactate + ethanol + organic acids). Since they can utilize pentoses and hexoses as carbon source and are tolerant to hop constituents, they can thrive in many places in breweries and end up spoiling beer. Lactobacillus spp. successfully grow at 30 °C and at pH 4–5 [8]. Below are some of the most familiar Lactobacillus spp. in brewing:

• L. brevis;
• L. lindneri;
• L. buchneri;
• L. brevisimilis.

The following are less common in beer and breweries [8]:

• L. casei;
• Lactobacillus delbrueckii subsp. delbruecki;
• L. fructivorans;
• L. fermentum;
• L. coryneformis;
• L. coryneformis subsp. torquens;
• L. curvatus;
• L. plantarum.

How they affect the beer? Even though not all Lactobacilli cause negative effect on the brew, some of them cause the most damage during final phases of beer production and after packaging. They give beer a silky turbidity and buttery flavor originating from diacetyl. Some Lactobacillus species are correlated with the production of extracellular polysaccharides (EPSs), which is recognized as viscosity increase [14]. However, this is more often contributed to Pediococcus spp. or even acetic acid bacteria [15].

2.2.2. Pediococcus

Pediococci are homofermentative cocci. Most common Pediococcus species in breweries is surely Pediococcus damnosus [8,16]. It can only found in beer, brewing yeast, and wines. In brewing raw materials or plant materials, it has not yet been identified. Other common pediococci are [8]:

• P. inopinatus;
• P. dextrinicus;
• P. pentosaceus.

P. damnosus can be determined in beer and during late fermentation (only sometimes in pitching yeast)

P. inopinatus and P. pentosaceus can be often found in pitching yeasts (but rarely found in late fermentation or beer).

Pediococci are related to sarcina sickness, which is manifested as acid formation with buttery aroma of diacetyl. Sometimes the ropiness in beers can be correlated to pediococci [8].

2.2.3. Leuconostoc

Heterofermentative cocci that are classified in the genus Leuconostoc are not as common in breweries. Leuconostocs found in breweries has been proven to be L. mesenteroides. However, there are no evidence that they cause beer spoilage [8].

2.2.4. Homofermentative Cocci

The only microorganism belonging to this group that can be identified in brewery is Lactococcus lactis. It can be held responsible for diacetyl production. However, there is no evidence that it can grow in beer [8].

2.2.5. Micrococcus and Staphylococcus

Micrococcus and Staphylococcus are not recognized as significant bacteria in the brewing industry, but they are found in beer and breweries and can be designated as beer spoilage bacteria. S. saprophyticus, S. epidermidis, and M. varians were detected in beer, breweries, and pitching yeast. M. kristinae is one example of an acid-tolerant and hop-resistant microorganism recognized as a beer spoilage bacterium. It thrives in somewhat high pH and low-bitterness products such as beer [8,16]. In anaerobic conditions, it is held responsible for a fruity aroma and an off-flavor [8].

2.2.6. Endospore-Forming Bacteria

These bacteria can cause infrequent problems in breweries, where they end up from raw materials such as cereals or other adjuncts. Spores can survive wort boiling. However, they cannot proliferate due to low pH of fermenting wort and beer. Additionally, they are sensitive to hops [8]. Thermophilic, endospore-forming bacilli have been isolated from brewery plant, malt, and sweet wort [8]. One example of such bacteria is B. coagulans. It is generally not detrimental for beer, but its ability to yield nitrosamine via the reduction of nitrate to nitrite is recognized as problematic [8].

Furthermore, Gram-positive bacteria and Gram-negative bacteria can cause problems in brewing, as well. The most important Gram-negative bacteria that can cause detrimental effect in breweries are s follows [8]:

Acetic acid bacteria;

• Zymomonas genus;
• Pectinatus cerevisiophilus;
• Pectinatus frisingensis;
• Selenomonas lacticifex;
• Propionispira raffinosivorans;
• Propionispira paucivorans;
• Megasphaera genus;

Some non-fermentative bacteria.

2.2.7. Acetic Acid Bacteria

Common bacteria found in breweries belong to Acetobacter and Gluconobacter spp. [17]. Acetomonads show resilience against the bacteriostatic activity of hops, acid, and ethanol [8], which results in beer spoilage. They can proliferate and spoil beer in the presence of oxygen. They usually affect beer quality by increasing acid, adding off-flavors, turbidity, and even ropiness [8]. Acetobacter spp. enjoy the ethanol and Gluconobacter spp. chooses sugars as a carbon source.

2.2.8. Enterobacteriaceae or Enterobacteria

Enterobacteria are mesophilic microorganisms; they can slowly grow at high temperatures, but they are not strictly thermophilic. They can be found in wort as coli-aerogenes or coliform bacteria [8].

The following common species are found in breweries [18,19,20]:

• Enterobacter aerogenes;
• Enterobacter cloacae;
• Rahnella (R.) aquatilis;
• Hafnia alvei;
• Obesumbacterium proteus;
• Citrobacter freundii;
• Klebsiella pneumoniae;
• Klebsiells oxytoca;
• Serratia strains.

Proteus mirabilis can slow down or accelerate the fermentation process and significantly influence the flavor and aroma of the final product.

O. proteus is designated as an important beer spoilage microorganism since it shows the ability to proliferate beside yeast during fermentation; it usually contaminates the pitching yeast. It can slow down fermentation, which can result in high final specific gravity beer and high pH [8]. This microorganism produces dimethyl sulfide, dimethyl disulfide, n-propanol, isobutanol, isopentanol, 2,3-butanediol, and diacetyl. Beers contaminated with O. proteus display a parsnip-like or fruity odor and flavor [8].

Another microorganism from this group is R. aquatilis. It enjoys hopped or unhopped wort, inoculated or not. It can successfully survive the brewing process and ends up in reused pitching yeast [8]. When high-gravity brews are in question, this microorganism gets killed by ethanol concentrations of 11–12% v/v. Depending on the beer style, ale or lager, it rises to the surface or settles down with the yeast cells. R. aquatilis significantly affects the brewing process and impairs beer flavor and aroma. It produces high levels of diacetyl and dimethyl sulfide [8].

2.2.9. Zymomonas

Contamination with Zymomonas results in beer with a rotten apple or fruity odor. It is a significant contaminant found in ale breweries and has not been reported in lager breweries. This is probably due to the lower temperatures during lager fermentation [8].

2.2.10. Megasphaera

This Gram-negative cocci results in brews with cloudiness and unpleasant odors. It produces butyric and caproic acids and smaller amounts of acetic, isovaleric, and valeric acids. Megasphaera is recognized as a true beer spoiler, but M. cerevisiae is sensitive to alcohol and low pH; thus, it does not proliferate in beers with ethanol content above 2.8% v/v [8].

3. Other Contaminants in Homebrewing

Besides microbiological contamination, many other physical contaminants can end up in beer. Such contaminants can be any physical body (rocks, metal parts, insects, hair, etc.) that ends up in the brewing process. Some of the stages of the homebrewing have natural protection or removal of physical contaminants, for example, lautering. Since many homebrewers brew their beer in various environments such as garages, yards, and gardens, the possibility of physical contamination is significantly high. Namely, brewing under trees will probably end up with any kind of contamination such as leaves, small branches, insects, animal hair, bird excrement, etc. [21,22]. Similarly, brewing in garages could result in different smells that end up in beer from volatile compounds from paints, oils, or metal parts that can end up in beer with raw materials, etc. The best way to prevent this is to cover the boil kettle, brew indoors, preferably have some kind of brewing station/corner prepared specially for brewing, and wear hair nets to ensure the absence of hair in the brew.

Cleaning and sanitizing agents have to be properly rinsed (if this is the recommendation by the producer). If not, this could lead to chemical contamination, which can deteriorate the quality beer. In the worst case, this could lead to poisoning the consumer. Also, many of these chemicals could negatively affect the yeast cells and halt the fermentation. To avoid such situations, producer’s recommendations should be followed to prepare the cleaning and sanitizing solutions [21].

4. Hot Spots in Homebrewing

There are some generally known hot spots in brewing industry; they are usually regulated with some safety management system (SMS) such as HACCP (Hazard Analysis Critical Control Points), FSMS (Food Safety Management System), ISO norms (International Organization for Standardization), SFBB (Safer Food, Better Business), GHP (Good hygiene Practice). The brewing industry implements many of these, but smaller breweries and especially homebrewers are not familiar with the concept of an SMS. This could be problematic in ensuring the cleanliness and safety of the final product.

Many problems may arise during homebrewing in terms of microbiological and chemical safety. To elaborate, primarily on the part about the microbiological safety: microorganisms are inevitable. They surround us, and homebrewing conditions are not ideally sanitary and rely mainly on the perception or experience of homebrewer. At the inception of homebrewing, homebrewers used typical home cleaning agents, such as bleach or plain detergents [23]. Nowadays, modern cleaners intended for homebrewing can be used. This means that you can use acid-based or iodine-based agents that require no rinsing [23]. Some of the homebrewing equipment can be sanitized by exposure to heat. For better understanding and visualization of homebrewing process, Figure 1 shows homebrewing process from mashing to fermentation. In Figure 1, it can be noticed that mashing and boiling temperatures are above pasteurization temperature, and they are kept at this temperature for 1 h, thus ensuring aseptic conditions. However, after the point of boiling, the wort is subjected to cooling to the fermentation temperature, which can range from 10–25 °C, and if kveik yeast is used than fermentation temperature can be set up to 35 °C. If the fermentation does not start fast, the chances for microbial contamination are higher. Elaboration of homebrewing points follows.

Here are some of the most important hotspots in homebrewing:

• Cleaning and maintaining the water preparation unit. Many homebrewers have small ultrafiltration of reverse osmosis (RO) units to obtain the desired level of minerals and salts in brewing water (liquor). However, these units need to be cleaned regularly, and the filters need to be changed. Over time, they lose the ability to deliver the desired quality of liquor. Liquor usually undergoes high temperatures, mashing at 65–70 °C, and boiling at 100 °C, leaving microbial contamination a minimal window to proliferate in later stages of fermentation and lagering. However, the water conductivity may deplete with time, which can lead to changes in pH values in wort and subsequently beer. Water can always be boiled prior to usage [24].
• Cleaning and maintaining the boiling kettle. Homebrewers usually have all-in-one system where mashing and boiling occur in the same kettle. Wort is a sweet liquid, prone to microbial contamination; thus, every part of the kettle should be thoroughly clean. Again, the temperatures in the kettle reach 100 °C and are kept like this for an hour or more, so there is a small chance of microbial proliferation in the further stages of brewing, but proper cleaning and sanitizing measures have to be implemented prior to and after boiling. Especially important is to sanitize the faucets. This can be carried out by spraying the faucet with ethanol (70%). Homebrewers commonly run hot wort (100 °C) through the faucet in order to sanitize it. Cleaning should be carried out after every boil. Common household detergents suffice, but for a more serious clean, professional homebrewing detergents and cleaning agent can be used. They can be purchased at different brewing equipment stores or online. When preparing wort for darker beers (which involves darker or roasted malts) it usually results in more debris on the kettle and heater pipes (in some systems, the heater is exposed to wort in the kettle). This usually means more furious scrubbing to remove the dark deposits with the use of some kind of commercially available cleaning agent, which should be used as prescribed by the producer [23]. Usually, this can be removed by applying phosphoric acid cleaning solution heated up to 60 °C for 15–30 min. After this time, the solution should be drained from the kettle, which should be refilled with hot water with non-caustic alkaline cleaner. The temperature should be kept at 60 °C for the same amount of time. Putting on safety glasses and gloves prior to working with these chemicals is very important. All the debris should be soft and easily removable by scrubbing with a plain scrubbing sponge [20]. All liquid should be drained and rinsed well with tap water. The kettle should be left to dry. If using a household detergent, one should be very careful to completely rinse it, because the foaming agents from it could later influence the quality of the brew. Often, homebrewers use cheap and affordable oxy-cleans, which give good results in cleaning hard core debris from the equipment [23].
• Cleaning and maintaining the cooler. Similarly, as with the kettle, the cooler can harvest protein, carbohydrates, and hop debris. Since the temperatures during cooling are not as high as during boiling, the debris on the cooler are much easier to clean. A simple wash with sponge and detergent is usually enough. However, due to hard water, carbonate debris can be problematic inside the cooler, and thus sporadic rinsing with some kind of weak organic or inorganic acid (e.g., citric, phosphoric, vinegar) can be conducted. The cooler can be immersed into such solution and left in it for 30 min, then drained and left to dry. The cooler can be easily sterilized by placing it on the kettle 15 min before the end of boil and then immerging it in the hot wort [23].
• Cleaning and maintaining the fermenters. As one of the key elements in homebrewing, fermenters should always be clean and sanitized prior to use. There are different fermenters on the market, made from glass, stainless steel, or plastics. The most commonly used in homebrewing are plastic fermenters. The principal of cleaning and sanitation of all of them is the same—prior to use, they should be thoroughly sanitized with ethanol or some other sanitizing agent properly prepared according to the producer’s recommendation. They can be sprayed or simply rinsed with sanitizing agent. Since plastic containers are not as durable as those from stainless steel or glass, their surface tends to get rough with time, especially after intense scrubbing. Thus, plastic fermenters should be replaced much more often than stainless steel or glass. After fermentation, hop resins, proteins, and yeast are all precipitated in the fermenter. Spent yeast makes up the majority of waste materials that have to be removed from the fermenter. The most efficient way is to rinse the yeast out and then thoroughly scrub the hop resins and residues from the fermenter walls with detergent. Special care should be dedicated to faucet on the fermenters. They can be tricky to clean. However, a deep soak in a detergent, rinsing, and drying should do the trick. Sanitation is not necessary right after cleaning if the fermenter will not promptly be used for another batch [24]. Prior to every use, fermenters and belonging faucets and lids should be rinsed with sanitizer or ethanol.
• Cleaning and maintaining the kegs, bottles, corks, and filling equipment. This is the final destination for the brew and has a significant impact on the final safety and health of the beer, since kegs and bottles can be contaminated with microorganisms, or improper sanitation can cause their proliferation [24].

The most efficient way to store a homebrewed beer is to transfer it to a keg. There are different types of kegs, but they can all be cleaned fairly easy. They should be regularly cleaned (scrubbed) to avoid the formation of beer stones; usually, weak organic acids or commercially available sanitizers are enough to sanitize the kegs. In case beer stone forms, the procedure for cleaning is as follows [25]:

• Wet the stone with an acid-based cleaner;
• Let it sit up to 15 min;
• Add non-caustic cleaner in hot water (no previous rinse of acid);
• Rinse the non-caustic cleaner with water.

Another popular form of packaging is glass bottles. They can be immerged into the sanitizing solution and left there for 30 min. It is important for the fluid to completely fill the bottle and to avoid air pockets. After, they are to be cleaned with brush and rinsed with hot water. It is best to let them air dry [26]. Another way is to put them in the dishwasher and run the hottest cycle. This will ensure sterilization. Since homebrewers reuse the bottles, it is best to clean and sanitize them right after use. Otherwise, molds (or other microbes) and yeast will form deposits, which will be hard to clean. In case this happen, it is important to clean the debris by thorough scrubbing, sanitize the bottles, and preferably subject the bottles to sterilization. Some dishwashers have this program. Sterilization can be carried out by putting the bottles into oven (180 °C) for a few minutes. They should be cooled gradually to avoid breakage. Cleaned bottles can be sprayed with ethanol.

Hoses used for transferring the beer from kegs to fermenters should immediately be rinsed with hot water, immersed into sanitizing solution and left in it for 15 min. Hoses should be hung and left to air-dry.

Besides the bottles, bottle caps should be sterilized as well. This is usually achieved by leaving them to soak for 10 min in a solution of sanitizer prior to use. They can also be boiled for a few minutes.

Bottling equipment (Figure 2) is commonly very primitive and is easily cleaned. Bottling with manual bottle capper is simple and usually very clean, meaning no excess dripping that could cause any problems with sanitation. A bottle capper can be usually be cleaned with a wet and clean wipe or sponge, and no previous sanitation measures are necessary prior putting the bottle under the capper.

Plate chillers or any other hard-to-clean parts (pumps, ball valves) should be cleaned by soaking them in sanitizing solution or rinsing them with it [27].

6.

Cleaning and maintaining the dispensing systems. Dispensing systems are an important part of homebrewers inventory. However, they need to be kept cleaned regularly. Draught line cleaning should be conducted every 14 days, and the following procedure should be applied [28]:

• Rinse the leftover beer from lines by using warm water.
• Rinse lines with 2–3% caustic-, acid-, or silicate-based solution (25–45 °C) for 15 min minimum.
• All faucets and hand-cleaned couplers should be washed by hand after disassembly.
• Rinse lines with cold water and no visible debris should be flushed from the lines.

Acid cleaning should be conducted every 3 months using the following procedure:

• Rinse beer or caustic cleaner (acid cleaner is in addition to caustic cleaner) from lines with warm water; rinse lines using acid cleaner.
• Rinse with acid solution through the lines for 15 min and then rinse lines with fresh water and no visible debris is being carried from the lines.

Every 6 months, hardware should be cleaned:

• Disassemble, service, and hand-clean all fob devices (i.e., beer savers, foam detectors).
• Disassemble, service, and hand-clean all couplers.

Along with sanitation with caustic solution, a recommendation is to mechanically clean the pipes every 14 days with a small sponge ball prior to rinse with clean water. Rinsing is recommended until the pH matches that of tap water.

7.

Cleaning and maintaining the cleaning equipment. Last but not least is taking care of the cleaning equipment. Sponges, wipes, rags, and brushes can be one of the most significant sources of contamination. Thus, they should be cleaned right after use and with suitable cleansers (detergents or sanitizers). Wipes and rags should be boiled after use and dried. All brushes and sponges should be rinsed with detergent and warm clean water and left to dry [23].

Cleaning agents best fit for homebrewers are all types of non-caustics. Caustics are commonly used in breweries, but they require serious safety measures and can damage the homebrew equipment. Thus, non-caustics are far more accessible for homebrewers and give better results. Caustic cleaners act to hydrolyze or emulsify the soil, and non-caustics use displacement chemistry to remove the dirt.

Post-rinse sanitizing agents that give the best results in homebrewing are chlorine dioxide, peracetic acid, iodophor, and phosphoric acid/anionic surfactant. Chlorine bleach and quaternary ammonium compounds are not as desired in homebrewing (or brewing in general) [25]. Some of the common sanitizers in homebrewing are listed in

Table 1. Some of the common homebrewing sanitation agents (adjusted from [23,29]).

Agent/Combination	Use	Rinse	Contact Time	Problems
Chlorine dioxide	Sanitize corks, hoses, carboys, bottles	NO	-	Expensive Requires activation with acid Short storage time when activated
Sodium hypochlorite	Solution/sanitize corks, hoses, carboys, bottles Remove soil	NO	up to 30 min	Hard on steel Off-flavor
Iodophor	Stainless steel fermenters, bottles, kegs Spray or submerge brewery parts for sanitization purposes	NO	1 min	Stains plastics Off-flavor
Phosphoric acid/anionic surfactant	Fermenters, bottles, kegs	NO	1–3 min	Extremely foamy Not safe for aluminum equipment
Quaternary ammonium compounds	Brewing equipment	NO	-	Suppresses the foam Off-flavor
Oxygen wash	Brewing equipment	YES		Not safe for aluminum equipment

.

5. Mind the Yeast

Homebrewers tend to use purchased yeasts, commonly dry. Adding such yeast into the wort is simple and requires no preparation and propagation of yeast. Just make sure that the temperature of wort is adjusted to the chosen yeast, open the bag, sprinkle yeast onto the wort, close the lid, and put on the air lock. Air lock should be filled with the solution of alcohol, sanitizing agent, or acidified water. However, some brewers like to re-use the yeast and this requires more action and higher sanitation measures. Namely, one can propagate used yeast (e.g., yeast from the bottom of bottles of commercial non-filtered beer or yeast that provided by a fellow brewer) [30]. To propagate yeast cells, it is important to ensure impeccable sanitation measures. This starts with the propagation flasks (no matter what size); they need to be cleaned and sanitized with any of the sanitation agents, just as the equipment does. It would be useful to sterilize it with heat as well. In homebrewing conditions, that would mean to put it in the oven at 120 °C for 15 min or rinse it in dishwasher at the highest temperature. Sterile wort should be used for propagation. Wort can be added directly after boiling, which is a 100 °C temperature, or it can be heated to 100 °C in a cooker, then cooled down to inoculation temperature (depending on the type of yeast to propagate). Propagation requires a magnetic stirrer, which ensures the proper mixing and aeration, so the magnetic stir bar also has to be sterile, sprayed with ethanol or any of the sanitizing agents. Some homebrewers insert a small aeration stone or sterile filter [31]. Common methods of cleaning involve soaking the stone in some sanitizing agent until it absorbs the solution (few minutes), boiling it in distilled water for 15 min, or heating it up in the oven at 170 °C for 1 h [27].

As mentioned in Section 2 (Common Microorganisms in Brewing), yeast can be contaminated with other microorganisms and thus should be rinsed prior any propagation, especially if it is being reused. A quick rinse using phosphoric acid to acidify the yeast slurry (pH 2.2–2.5) at 2–4 °C for 2 h should be applied. A gentle stirring to protect the cells against damage can also be applied [32]. This process does not remove the wild yeast, but it is effective against most bacterial contamination.

Even though wild yeasts are mostly unwanted in breweries, some are an essential part of special beers. For example, Brettanomyces, which are commonly referred to as spoilage microorganisms in breweries and wineries. However, in some beer styles, such as Belgian lambic and gueuze beers, it can be crucial for bringing out the specific aromas and tastes [33,34]. The most common species belonging to Bretanomyces are Brettanomyces bruxellensis and B. anomalus [34]. These yeasts affect the organoleptic properties of the product, contributing to the unique sensory properties of special beers. Secondary metabolites produced by Brettanomyces are often related to undesirable flavors, designated as horse sweat, barnyard, medicinal, or leathery [35]; thus, they are not desirable in regular and standard beers such as lagers.

When transferring to a bigger flask or wort container, the flask neck should be exposed to heat (burnt with fire). This is applicable only to laboratory-grade flasks; otherwise, high temperature might lead to glass breakage.

6. Infestations

Besides the microbiological risk of contamination, homebrewers often have trouble with various insects that degrade the malt quality [36,37]. Homebrewers frequently order bigger amounts of malt in order to save money, since malt prices are volume-related [36]. The following are the most common insects that can be found in places where malt is stored [37,38]:

• Weevils—Sitophilus granarius, and S. oryzae, otherwise known as “granary weevil”.
• Saw-toothed grain beetles—Oryzae philussurinamensis.
• Flour beetles—Tribolium castaneum or “the rust red flourbeetle”.
• Khapra beetles—Trogoderma granarium.
• Moths—not specified.
• Outliers—cockroaches, crickets, fleas, etc.

Infestation control often involves rodents, but a similar method for reduction can be applied as follows: To efficiently reduce the possibility of infestation, it is important to maintain a clean storage and brewing environment. All seams and corners should be caulked up to remove bug ingress. Flat surfaces should reduce to a minimum and kept dust-free. Temperature should be lower than 20 °C; this should reduce the possibility of reproduction. Air humidity should also be monitored and should be below 60%. Vacuuming should be possible everywhere, behind shelves, equipment, around malt bags, or containers, and should be conducted regularly. Glue traps should be placed to locations that are hard to clean.

Usage of smaller bags (2.5–5 kg) instead of bulk sacks can help reduce the possibility of infestation as well. Plastic and sealed containers to store the malt in are often helpful. Brewing adjuncts should be kept separately from malt, and any opened bags should be sealed or wrapped in cling foil.

7. Conclusions

Homebrewing is a rising hobby. Many people are developing homebrews, and they are usually self- or internet-taught, without any previous formal knowledge of microbiology, biochemistry, or hygiene and sanitation. This can cause problems in the final beer. This paper gave an overview of potential hazardous points in brewing—hot spots to which attention should be paid to avoid contamination and to deliver a healthy and safe final product. It is impossible to control every homebrewer and how they conduct the brewing process, but luckily, many websites provide verified information, and some associations even support homebrewers with information, advice, and courses that can help improve homebrewed beer production. The broad public that makes up homebrewers is receptive of scientific and professional advice; thus, communication between these parties should remain open.