This hobby isn't particularly dangerous but there are a few things to keep an eye for to stay safe and uninjured. These points aren't designed to make people paranoid and aren't necessarily guarantee these events will happen. They are just here so you can pay mind and prevent them from happening.
This is preached endlessly for good reason. It produces drinkable results without toxicity. See our article on sanitation for more information. Also see Microbes & Infections below as well.
Many fermentors are glass. Glass is resistant to scouring/scratching, many chemicals, leaching, and has low permeability to oxygen. However, glass is fragile and prone to breakage, which often causes injuries as well. Speculation about newer production being cheaper and thinner glass may feed some of these concerns. There's no definite conclusion except following good handling procedures for glass to maximize the lifespan and minimize the breakage and injury as a result.
Typically, 1 gallon or 4L jugs do not suffer the same issues as larger (mostly 5 gal/19L+ sizes) since they are small and easy to handle. Regardless, treat them with caution and follow good handling guidelines.
Some basics should be observed. Know your limits on what you can lift, full fermentors can be very heavy and awkward to carry. Never attempt to lift a wet carboy. Position the carboy where it will stay before filling it.
A video detailing common issues with carboys by some manufacturers is a recommended watch. It goes over the common problem sources, how to identify them, and which products to chose or avoid. Poor annealing is common problem and deals with internal stresses of the glass and is common among cheaper carboys, typically Mexican-made products. More expensive Italian-made carboys are annealed and do not suffer the same problems (when handled appropriately).
Inspect it for damage between batches. They can develop cracks, chips, or other signs of damage. It is better to find a crack on an empty carboy instead of it breaking when full, or worse, breaking while you are handling it and it injures you.
Use a lifting adjunct. There are products for these and some are better than others. However, the single best and easy-to-obtain one is a milk crate. It is durable, has handles, and will not break. Carboy straps tear and carboy neck handles shear off necks.
Do not use marbles. Marbles have been recommended in homebrew for a long time as an easy way to bulk out space in a carboy and eliminate headspace. It is not recommended for a few safety reasons. The safety reason is it dramatically increases the weight of the fermentor. Secondly, the act of dropping pounds of glass beads from high up to strike the bottom has a chance of cracking the glass at the bottom. Be smart, plan ahead, and do not use potentially unsafe practices. See our bulk aging section for more about headspace mitigation.
Plastic isn't prone to breakage like glass is. It can harbor infections if not cleaned properly. Avoid using scouring pads, abrasives, or wire brushes against it. There is debate about the effect this actually has in real world brewing. For the purpose of safety, it will be suggested on this wiki.
Only use food-grade plastics. HDPE and PET are top of the list but make sure specifically they are food-grade. Non-food-grade plastics exist. Do not attempt to reuse non-food grade plastics or plastics that held chemicals. It is far too easy and cheap to get (even reuse) appropriate food-grade plastics as opposed to try and clean something not suited for the job.
There isn't much to keep in mind with safe practices using stainless. It is the most durable and do not have safety downsides like other types. It does cost the most.
Always add ACID to the full volume of WATER
The one concern is a process called passivation. This is a type of controlled 'etch' that gives the stainless a passive coat that is resistant to further corrosion. Stainless without this coat can introduce metallic (iron, nickel) into brews. It's not necessarily dangerous unless someone has a nickel allergy.
To passivize, prepare an acid solution and allow that to rest in the fermentor for at least 30 minutes. 1 oz of star san per gallon (this is 5x the normal usage) or a 5% citric acid solution can be used. Fill it to at least slightly above where you plan to use. Allow to stand, drain out. Do this before first usage and reapply periodically if the inside becomes scratched at all. You may notice a metal smell or the water turning blue, this means your passivization is working.
Nitric acid can also be used but is a hazmat and not commonly available to homebrewers. Safe handling of ALL acids and PPE (especially eye protection) is ALWAYS recommended. Add acid to the full volume of water to keep concentrations no higher than they ever need to be to prevent injury.
Pressure fermentors and other pressure-rated equipment now available to homebrewers. The original purpose was to allow lagers to be fermented above lager temperatures without creating style-inappropriate esters. It can also be used to carbonate a beverage during fermentation. It has increased safety concerns and should be taken seriously.
Never exceed the rating of your equipment. Period. This is unsafe. Similarly, use a spunding valve. Check your equipment between uses. Follow your products guidelines for conducting pressure tests. Replacement faulty components.
There are vacuum pumps which can be used for rapid degassing. The safety risk is not using vacuum-rated equipment. Many bottles are not, especially glass carboys. Even macro-scale breweries have trouble with vacuum pressure in stainless steel fermentors getting imploded from mixing improperly mixing caustic cleaning cycles without vent lines open. This serves to demonstrate that higher pressure rated equipment does NOT indicate vacuum-rated.
The safest solution to this is to use a properly-rated vacuum chamber and can be bought online. They are typically steel (ensure food-grade stainless 304 or 316) with gasketed acrylic lids.
We have a page about infections already. This is a safety-oriented section only. Yeasts are safe to use and consume in small amounts (some may experience gastric disturbances howveer), especially commercially obtained ones. A 'vinegary' taste is often not an infection. Those new to brewing may underestimate how acidic something is naturally. Compare to actual vinegar and consult acid-tannin balance for flavor improvement steps.
The chief concerning agent is mold of any variety. Molds are capable of producing mycotoxins that affect humans and pose serious health risks. The toxins are excreted and still present, even if the the mold is gone. Scooping out the mold is not enough to save the brew. Be smart, use sanitary practices, punch down any fruit caps, do not keep any moldy brews. Be extra diligent about sanitizing vessels that had mold previously grow in them.
Bacteria may also infect brews. Many do not produce toxins, notable exception is C. botulinum known for botulism. It is toxic and dangerous and the reason why it is not recommended to feed honey to infants 2 or under. It is typically not a problem for humans consuming honey properly handled (even raw, unfiltered honeys).
Botulism is prevent in mead by a pH 4.6 or below. It is normal for mead to be below this by they honey's acid contributions alone. Excess buffering or raising pH isn't recommended since it allow C. botulinum to grow and does not always help the final product. Botulism is dangerous but also rare and not an issue with honey when making mead normally.
C. botulinum may infect honey that is too wet and allows the microbe to survive. In the US, the FDA regulates the amount of moisture of a honey product before it can be sold and all sold honeys exceed this. The notable exception is sometimes farmer's market folks will offer unsellable moist honey for free (or at a discount, feel free to haggle since they cannot legally sell it).
Other bacteria may get into the brew and contaminate it, typically causing sourness. It isn't necessarily dangerous but can have negative flavor impacts. Additionally, bacteria may cause over attenuation of beer or braggots, thus bottle bombs. See below for more info.
It is possible to brew with cultures from other sources than commercial yeast. These are safety risks associated depending on what the culture is and how it was obtained. This should only be attempted if you know what you are doing and the risks involved. More information is available on our yeast page, including short sections about non-commercial cultures.
The term bottle bomb is for any bottled product actively fermenting that bursts the bottle. Crown cap bottles are most often the offenders since corks do not hold pressure and are merely pushed out. Swing-top bottles often do hold the pressure but have been known to explode upon opening (complicated physics but the sudden rush causing the neck to blow out, sending exploding glass presumably where you hands and fingers are). The exception for swing-tops are square or 'flask'-shaped bottles. They should never be used to hold pressure since they are weak.
This is easy for still (non-carbonated) drinks. Ferment dry, properly stabilize (there are several methods here), or use unfermentable sweeteners (such as erythritol). Many options are available very easily to homebrewers.
For bottle carbonated drinks, use appropriate amounts of priming sugar is key. Using a priming sugar calculator, like Northern Brewer's, will tell you the amount of sugar per CO2 volumes you need. Exceeding or miscalculating can cause bottle bombs. Use appropriate rated bottles. The safest way to maintain sweetness in bottle carbonated drinks is use to non-fermentable sweeteners.
ON BRAGGOTS: Braggots contain malt, therefore are partially unfermentable carbohydrates to yeast. There are bacterial infections which can metabolize these dextrins and can work after the yeast are done. This leads to bottle bombs even after stable terminal gravities. There are other diastatic yeasts (like Saison yeasts) which are STA-1+ which can ferment more of the fermentables than other beer yeasts typically can. In both cases, use proper sanitary practices to prevent contanimation. Use extra precautions if you have any of these contaminations or use other cultures in your brewing practices.
Not a recommended process if you don't know exactly what you're doing. This is a practice sometimes referenced by homebrewers by using dry ice as opposed to priming sugar to pressurize a keg. The expansion ratio of CO2 is 535:1 meaning that it expands 535x when it sublimates from a solid to a gas. It can cause tremendous over-pressure problems because it will quickly melt and release all of the gas, which dissolves slowly. This has the potential to cause keg bombs, which are far larger and more dangerous than bottle bombs. A CO2 regulator slowly adds a fixed amount of pressure. This keeps it at safe levels will it dissolves.
If you have kegs and need pressure for serving, you probably have a CO2 tank. Just use it. CO2 is cheap.