Stainless 304 L, 316 L, glossy finish 2b, bright annealed... We can be easily lost in the stainless steel world. Behind these terms are hidden differents types and finishes with precises features and properties. Let's have a look at this.
You will find stainless 304 L and stainless 316 L. The L means Low Carbon: indeed lower carbon technology leads to stainless.
These two types have a similar composition except one element: we find carbon, nickel and chrome in both, and the 316 L has molybdenum in addition.
This component improves corrosion resistance in acid, phosphoric and sulphur environments.
Usually, for averagely harsh environments like red wine, stainless 304 L is suitable. However, for harsher environments like white wine, rosé or cognac, stainless 316 L is advised and even mandatory for brandy.
Mixed use is possible: stainless 304 L for vat's body and 316 L for roof and chimney. This method is used in case of neutral gaz protection to wine conservation.
Three finishes are used on the market: the glossy finish 2B, the wine polish, and the bright annealed. What's the difference? Each finish has a different roughness index (Ra). Smooth surfaces (= low Ra) avoid tartaric acid adhesion.
In roughness decreasing order, glossy finish 2B has a Ri 0.20, wine polish is between 0.15 and 0.17 according to our estimations (nothing is imposed about wine polish's Ra), and bright annealed is 0.08.
Bright annealed, contrary to glossy finish 2B, is annealed under controled atmosphere, giving this surface smoother and easier to clean.
This interior finishing is manufactured by a company based in Germany and Italy. It has been repurchased and the parent company has restructured the group closing the italian factory and grouping all productions in Germany. This has totally disturbed the bright annealed stainless steel market and has forced wine industry suppliers to find an alternative.
The wine polish appeared on the market. It's a mechanical polish which can reflect light without reaching the smoothness of a bright annealed stainless steel.
One of the most common outer finishing in the wine industry is the polished Scotch Brite. In our factory, we use our own polishing machine to make a thin polish and give this well known brushed finish.
The polished grain 220 is less thin, and is also used.
And what about the "bouchonné" finishing ? We're talking about little concentric polishings juste like the picture below.