The 304/304L/316/316L AISI class stainless steel used on BacBrewing products is a chromium-nichel and chromium-nichel-molybdenum austenitic steel. Without focusing too much on the chemical specifications of stainless steel, to understand easily and effectively why some surface treatments have to be done on an object made of stainless steel let’s start by saying that stainless steel is a low-carbon steel with chromium. Chromium reacts with air and forms oxides on the surface with a penetration between 0.2 and 5 nm: this makes the steel “stainless”, or at least, it will hardly present signs of rust, only surface deposit after being passivated. That’s the reason why stainless-steel pieces are not stored together with ferrous material.
Let’s go into details on why a stainless-steel piece for food use have to withstand chemical treatments. If we take a sheet of steel that usually had time to passivate while stored and we sand it, we plastically deform it (cut, bend) or we treat it thermally (welding etc), the chromium oxide on the areas we worked on will vanish and the steel will no longer be protected. We then need to reform the oxide, but to do so we have to get rid of the blue/brown thermal “stain” (in the case of welding) or we have to get rid of the carbon (in the case of plastic deformation, cut or bending). The blade of the cutting machine and the prism of the bending machine have to be made of hard quenched metal so they contain carbon inside and this will pass to the stainless steel. This is the reason why before bending it a stainless-steel piece is not magnetic, or very poorly magnetic, while after bending it, it will attract the magnet. That’s the sign the carbon from the blade has transferred to the metal.
Pickling from 30 minutes to 3 hours can eliminate any trace of carbon. At this point the piece is ready for the finishing process with rotating cotton pads and polishing pastes or with a galvanic electropolishing. In both cases the roughness of the stainless-steel surface will be smoothed and the ambient light won’t be reflected everywhere but with the same angle, that’s why a smooth surface looks shiny. Polishing makes the metal look good and makes the cleaning easier. Once washed and dried, the piece is now ready for the passivation. BacBrewing uses a total immersion process. To be called “passivated” a piece has to stay at least 30 minutes inside the bath. The level of penetration the chromium oxide gives is the least to say the piece is suitable for food use. If it spends an hour, the penetration rate will increase gradually, when we’ll reach 3 hours the difference won’t be much and the rate can no longer be increased.
Nothing comes out the BacBrewing laboratory without being treated, even if the customer is in a hurry, the immersion time has to be at least 1 hour for pieces that won’t come into contact with food (17/19mm wrenches for instance) and more than 3 hours for everything that come into contact with food. Usually passivated pieces will be put inside in the evening and taken out in the morning. At this point, after the umpteenth washing and drying, they are ready to be sold.
In summary, if you’ll find stainless steel articles sold at better prices than ours, as often happens for example on social media, like hop baskets, be careful. Many still have welding stains, some even have the code still printed inside! This means they have not been treated because the suitable treatments can only be done backwards, this means that passivation can only be done if the object has been pickled too. Are they toxic? No, but they don’t meet the EU and US requirements: even if they are made of stainless steel, they can’t be certificated for food use. The quality of the product as always depends on many factors, from the material used, the acidic, the labor... that’s why quality has a significant cost, often more expensive than the material itself.
What raises the price is also the MOCA certification that certifies that the company, the process, the surface treatments done are correct and meet the requirements for selling stainless-steel products for food use. If you own a MOCA-certified brewery, something mandatory if you produce food, and use an economic non-certified hop basket all the plant will lose the certification with consequent fines.
Remember, quality has a price and nobody gives it for free!