Metallurgy

I have to admit, I am a chronic DIY’er. Give me a nice and shiny off the shelf brewing system and I would probably try to take it apart and customize it — like, give it wheels and steering. For many of us, half the fun of brewing is getting to make the equipment we use. For some of us, it might be more. Regardless, making equipment is part of the fabric of homebrewing. (Except for brewpots, not many people have the ability to deep-draw metals at home.)

Every homebrewer is faced with equipment choices, whether they make it themselves or buy it from a shop. The decision to make or buy an item usually involves determining the best combination of material costs, performance, and degree of difficulty for making that item. There are brewers that live by the mantra, “simpler is better.” There are other brewers that live by, “cheaper is better.” And there are a few that unequivocally state that, “the best is better.”

So, how do you decide? Each metal has its advantages and disadvantages depending on the product form and where you want to use it in the brewery. Aluminum and brass are often the most economical choices but require gentler handling and cleaning regimens than stainless steel. Copper has long been a favorite for do-it-yourselfers because it’s easy to cut and solder, but the cost has now increased to the point where stainless steel is often more economical. Stainless steel has always been the gold standard for brewing equipment due to its excellent corrosion resistance and durability, but the cost of an all-stainless setup can still be prohibitive. The availability of less expensive stainless alloys for valves and fittings is helping to change that however. Weigh your wants and needs and use the information in this article to build a brewery that works best for you.
For example, what material characteristics should you look for in a brewing pot? Some of the considerations might be better heat conductivity, ease of cleaning, cost and customization. Some brewers might consider cost to be the biggest concern, but short-term cost may need to be weighed against long-term durability or adaptability. Each material choice should be considered to the application, and how that application may change over time.

The ultimate brewing setup for many people would be all stainless steel, and completely welded so it won’t leak and can survive a magnitude 8 earthquake (or your kid’s clumsy friends). Welding is fine and dandy but not many people have the equipment and expertise to produce clean welds. It is often easier to braze or solder using tin-silver plumbing solder to attach threaded nipples to pots. Brazing and soldering can be done by almost anyone with a little practice. Alternatively, weldless fittings are available for many applications and have the advantage of disassembly
for cleaning.

Aluminum
Aluminum is a very good option, is low cost, has good conductivity, and good cleanability. The best thing about aluminum is that it’s easy to drill and accessorize, using weldless fittings to add a ball valve, sight glass or thermometer. Be cautious if you are considering buying an aluminum turkey fryer pot and burner setup however. Those pots are often quite thin walled and more suitable for annual turkey boiling than for use as a brewpot. An 8- or 10-gallon (30- or 38-L) aluminum stockpot from a restaurant supply store makes a great brewpot and typically costs 70% of stainless steel.

The aluminum alloys most commonly used for cookware are alloys 3003 and 3004, which have very good corrosion resistance. Under normal brewing conditions, aluminum (by itself) will not corrode and should not contribute any metallic flavor to your beer. The metal will season and turn dull with use. Do not clean the metal shiny bright between uses and you will minimize your chance of getting a metallic off-flavor.

Aluminum will corrode if placed adjacent to another metal like copper in wort, but the short contact time during a typical brew day is not a problem. Do not use bleach or caustic, such as EZ Off, because these will cause pitting of the aluminum. Percarbonate-based cleaners like Straight A and PBW, or unscented dishwashing detergent, are recommended for general cleaning.

The role of aluminum in Alzheimer’s Disease has been thoroughly discounted, but concerns still come up occasionally. A metallic off-flavor would be noticed long before a toxic level of aluminum could be ingested. Don’t clean your aluminum shiny bright, let it turn dull, and you will not have any metallic off-flavors. There is more aluminum in a couple of Rolaids™ antacid tablets than in an entire batch of beer brewed in an aluminum brewpot.

Brass
Brass is a group of alloys made from copper and zinc with some lead thrown in for machinability. The lead percentage varies, but for the yellow brass alloys commonly used in plumbing fittings it is 3% or less. Lead does not alloy or mix with the copper and zinc in brass, but instead exists as tiny
globules, like bananas in Jell-O. These globules act as a lubricant during machining and result in a micro-thin film of lead being smeared over the machined surface. It is this lead that can be dissolved off by the wort.

While this teeny, tiny amount of lead is not a health concern, most people would be happier if wasn’t there at all. Red brass does not contain lead and many states have legislated that plumbing alloys be lead-free. (See sidebar on the next page for a method to remove surface lead from brass.)
Brass can be readily soldered and brazed to copper and stainless steel. The thermal conductivity of brass is similar to aluminum, but the corrosion resistance of brass is more similar to copper. The reason that brass fittings are not commonly used in commercial breweries is that chemicals that are commonly used with stainless steel and clean-in-place (CIP) systems are too corrosive to copper and brass. As homebrewers, we don’t have to use such strong chemicals, nor are the parts in service 24 hours a day/7 days a week, so mixing different alloys/components is not a problem.

Brass ball valves are very useful on large brewpots, allowing easy transfer of hot liquid to a chiller or another vessel. Ball valves are available in brass, nickel-plated brass and stainless steel. A plain brass valve will last a very long time with proper maintenance. Nickel-plated or stainless steel valves are more stain resistant, but cost more. Nickel-plated valves and fittings are about twice the cost of plain brass, but 304 stainless steel valves and fittings can be three times the cost of the plain brass. Stainless steel fittings may buy peace of mind, but honestly a little cleaning and wiping of brass will buy nearly the same performance.

Copper
Copper has the highest heat conductivity, is easy to form and was traditionally used for making the brewing kettles or “coppers.” Copper can be readily soldered, brazed and welded with the proper equipment.

Copper is relatively inert to both wort and beer. With regular use, it will build up a stable oxide layer (dull copper color) that will protect it from any further interaction with the wort. Only minimal cleaning should be used to remove surface grime, hop bits and wort protein as necessary. There is no need to clean copper shiny-bright after every use or before contact with your wort. It is better if the copper is allowed to form a dull copper finish with use.

However, you need to be aware that copper can develop a toxic blue-green oxide called verdigris. Verdigris includes several chemical compounds — cupric acetate, copper sulfate, cupric chloride, etc. — and these blue-green compounds should not be allowed to contact your beer or any other food item because they are readily soluble in weakly acidic solutions (like beer), and can lead to copper poisoning (i.e., nausea, vomiting). To clean heavy oxidation (black), and verdigris, use vinegar, or oxalic acid-based cleansers like Revereware Copper and Stainless Steel cleanser. For regular cleaning of copper and brass, unscented dish detergent or sodium percarbonate-based cleaners are preferred. Cleaning and sanitizing copper wort chillers with bleach solutions is not recommended. Oxidizers like bleach and hydrogen peroxide quickly cause copper and brass to blacken; these oxides do not protect the surface from further corrosion, and quickly dissolve in the acidic wort. The trace metals like zinc are beneficial nutrients for yeast, but the amount of copper that can be dissolved from non-passive oxides can be detrimental to the batch.

While zinc is an important nutrient for yeast growth, it also can be too much of a good thing. Corrosion of brass can cause increased acetaldehyde and fusel alcohol production due to high yeast growth when zinc concentrations exceed 5 ppm. Excess zinc can also cause soapy or goaty flavors. But like copper, brass is usually stable in wort and will turn dull with regular use as it builds up a passive oxide layer. Brass should be treated like copper for normal cleaning.

Copper counterflow wort chillers should not be stored full of sanitizer or water. Any biological deposits can lead to corrosion in either water or sanitizer. Copper should be rinsed thoroughly with clean water and allowed to drain before storage.

Stainless Steel
Stainless steel does not have the thermal conductivity that copper or aluminum has, and scorching of wort can be a problem if the burner heating rate is too aggressive, but its cleanability is excellent. Large stainless steel pots can be quite expensive, especially if they have aluminum clad bottoms for better heat distribution. A good stainless steel brewing pot will last forever.

Stainless steels are iron alloys containing chromium and nickel. The types most commonly used in the food and beverage industry are the 200 and 300 series austenitic stainless steels. The 300 series typically contain 18% chromium and 8% nickel. The 200 series alloys use manganese instead of nickel and typically cost much less than the 300 series. They have similar corrosion resistance and machinability, and are weldable. The thermal conductivity of stainless steel is about 10 times less than aluminum.

The reason everyone likes stainless steel is the corrosion resistance and durability, but it’s not perfect. The key to stainlessness is a passive oxide layer that protects the metal below from the environment. The key to creating this passive layer is getting the steel surface clean and free of contaminants. The easiest way to do this at home is to use a sponge or soft scrubby and kitchen cleanser made for cleaning stainless steel cookware. Three examples are Bar Keepers Friend, Kleen King, and Revereware Stainless Steel cleansers. The active ingredient in these cleansers is oxalic acid, and it serves the same cleaning purpose as nitric acid, which is commonly used in industry, but is too hazardous for home use. Once the surface has been cleaned to bare metal, the passive oxide layer will reform immediately. These cleansers are an effective method for repassivating stainless after cutting, grinding, soldering, or welding, and work great for cleaning copper as well. Do not use steel wool or even a stainless steel scrubby
to clean discoloration; they will cause rust. Stainless steel is not invulnerable; any breach in the oxide layer by another metal, or formation of non-passive oxides due to soldering or welding, can initiate corrosion, especially in the presence of chlorides.

Stainless steel plate chillers, like copper chillers, should not be stored full of water or sanitizer due to the risk of galvanic corrosion. Plate chillers should be rinsed thoroughly with clean water after cleaning and allowed to drain before storage. Blowing the chiller dry with compressed air will surely help prevent any chance of corrosion during storage.

Bio-fouling (trub deposits) and beerstone scale (calcium oxalate) can also cause corrosion. The metal underneath the deposit can become oxygen depleted via biological or chemical action and lose passivity, becoming pitted. A two-step procedure is most effective for removing beerstone. Beerstone is a combination of protein buildup and mineral deposit, so removal works best if the protein is broken up with a caustic, like sodium hydroxide or PBW™, and then the remaining lime can be dissolved by an acidic cleaner like CLR™. Do not use swimming pool (muriatic) acid to dissolve beerstone or clean stainless steel. The acid used for swimming pools is actually hydrochloric acid, which is very corrosive to stainless steel if left too long.

De-leading Brass
The surface lead on brass is easily removed by soaking the parts in a solution of vinegar and hydrogen peroxide. You can get these at the grocery store or drug store. You can use white distilled vinegar or cider vinegar; just check the label to be sure it is 5% acid by volume. The hydrogen peroxide should be 3% by volume. To make the solution, mix them at a 2-to-1 volume ratio of vinegar to peroxide. Simply immerse the parts in the solution and watch for the color of the parts to change. The process takes just a couple minutes to clean and brighten the surface. The color of the brass will change to buttery yellow-gold when the lead is removed. The vinegar-peroxide solution should remain clear and colorless. If the solution starts to turn blue or green and/or the brass turns dark, it means that the parts have been soaking too long, the copper is dissolving and subsurface lead is being exposed. Make up a fresh solution and soak the parts again. This treatment only needs to be done once before the first use of the parts.

Why do Metals Corrode?
All corrosion is basically galvanic. The electrochemical difference between two adjacent metals in the presence of an electrolyte, creates a battery. An electrolyte can be any liquid such as tap water, salt water or beer. The more active of the two metals will ionize (or corrode). These metal ions will readily combine with oxygen to form oxides or other corrosion products. Corrosion can also occur between two adjacent areas on the same piece of metal, if the presence of dirt, a chemical, or a scratch can make the two areas seem electrically different from each other.

The relative surface area of the two metals also affects the corrosion rate. If the more passive metal has a larger surface area than the active metal, the corrosion of the active metal will be increased. If the active metal area is larger than the passive metal, the corrosion of the active metal will decrease significantly. In both cases, most of the corrosion will take place at the interface of the two metals.

All metals are electrochemically different from one another, covering the spectrum from very active (e.g. magnesium, zinc, aluminum) to very passive (e.g. titanium, gold). The more active metal will corrode in preference to the more passive. This property is often used for corrosion protection. Anodic protection is where an active metal (e.g. zinc) is plated onto a more passive metal (e.g. steel) part to protect it. The zinc corrodes instead of the steel. The problem with anodic protection is that the active metal is released to the environment (i.e., the beer). Cathodic protection is where a more passive metal is plated onto a more active, such as gold plating onto a steel part. The problem with cathodic protection is that a breach in the plating will cause the more active metal underneath to corrode rapidly. Nickel and chromium platings are often used on brass to protect the brass from corrosion and provide a more aesthetic appearance. Brass, copper, stainless steel and silver solder are close enough together on the galvanic series that there is not much potential for corrosion between them.

Metals can also be protected from corrosion by building up a uniform oxide film, similar to how a sun tan can prevent sun burn. But just like a sun tan, the efficacy of the oxide film varies and may not be proof against all corrosion. Some oxides are very passive and inhibit almost all corrosion, such as the chromium oxides that protect stainless steel. Other oxides are more reactive, like red rust and heat tint on stainless steel, and do not inhibit further corrosion at all.

Stainless steel is referred to as being “passivated” when the protective chromium oxide surface layer is unbroken. If this oxide layer is breached by iron (from a wire brush or drill bit) or dissolved by chemical action (like bleach) or compositionally altered by heat (brazing or welding) it will rust. The problem with stainless steel corrosion is usually not an off-flavor, but more often a hole in a valuable piece of equipment.

Most other oxides are somewhere in between, and can be used to protect the metal from specific environments. The oxides of copper, brass, and aluminum fall in this category. Copper and brass will develop a dull stable oxide over time that is resistant to corrosion in wort, but scouring the metal shiny bright will remove the passive film. To encourage a passive film on aluminum, copper and brass — wash the item thoroughly, dry it thoroughly, and then put it in your oven (dry) at 350 °F (177 °C) for about 10 minutes. This will help the anhydrous oxide layer to thicken. The highly corrosion resistant, dark anodized finish that is common on aluminum cookware is produced by electrolysis in a chemical bath and can’t be done at home.

Here is a good rule of thumb for preventing corrosion and metallic off-flavors: All metals should be dull-looking but still look like themselves. In other words, copper should look like dull copper. Aluminum should look like dull aluminum. They should not look black, or green or blue. Highly colored oxides are generally not passive oxides and will probably dissolve in wort and generate an off-flavor or promote staling.

Metals and Stale Beer
Aluminum, copper and brass are fine when in contact with the wort before fermentation, but detrimental afterwards. In the case of copper, the ions react with the hydrogen sulfide produced during fermentation and reduce it to insoluble copper sulfide, which is left behind with the trub and yeast cake. Switching to all stainless steel brewing equipment can lead to noticeable quantities of hydrogen sulfide and sulfur off-flavors and aromas in the beer. The use of copper wort chillers will provide all the copper necessary, as will including a short piece (1 inch) of copper tubing in the boil. In fact, small amounts of most any metal (except iron) can be neutralized or removed from the wort by the yeast, assuming that the fermentation is strong.

Contact with aluminum, copper and steel after fermentation is a problem because it catalyzes staling reactions, including the production of hydrogen peroxide, the neutralization of hop aroma, and oxidize the alcohols to aldehydes. Finished beer should not be stored in contact with copper, and even the short contact time in a copper coil in a jockey box can oxidize the beer. Stainless steel tubing is better for beer quality, even though the thermal conductivity is much lower. This is why you will see most modern breweries awash in stainless steel.

Choose Your Metals Wisely
Now that you have all the information you need, it’s time to decide for yourself if you should go for the simplest choice, the cheapest choice or the “best” choice. To help you make that decision, check out the chart above for a quick side-by-side comparison of cost, conductivity, cleanability, corrosion resistance, machining, soldering and welding quality of each metal. If you are like most homebrewers, most likely you will use some combination of each of these metals in your homebrewery, depending on what will work best for your setup based on your homebrewing needs and metallurgy skills.

Written by John Palmer