Filtration is used at different stage of the wine process.
But why? To rich a crystal clear wine, stabilize it and also protect the wine from micro-organisms the wine normally is filtered.
But how? First it is juice filtration: the lees and visible particles (10-50μm filter). This depends upon the variety of grapes and the style of the wine that is aimed for.
There are, then, 3 options. RDV (Rotary Drum Vacuum filter), the most popular, who require patience skill to build this famous « cake « of Diatomaceous earth, perlite or cellulose (filter media). It’s a Depth filtration type, that ’s mean, it’s not filtrated from the surface, the mode is by absorption and sieve process. The flow is perpendicular or called dead-end. it’s cross the filter media. The inconvenience to have a perpendicular flow is when the filter is saturated, nothing pass anymore. The difference of tangential-flow, who will be along the filter/membrane and can still circulate even if the filter is full of particles. Problems of RDV, it can be time consuming and produces waste(post harvest). During Harvest, sludge can be composted or sprayed under certain conditions.
Second option is floatation, fast but have to be precise (temperature, etc) to made it works properly.
Last method is by centrifuge. It is quite expensive by machinery price compare to small amount it can treat
After what ever coarse methods, the wine is still cloudy. Yeasts and other compounds are still in the wine, it is up to 100NTU. We measure the clarity with NTU (nephelometric turbidity unit).
The fine filtration gets rid of yeast and other microbes (2-0,65μm filter). So the wine get transparent, and it can also fixe or prevent some microbial problems. Fine filtration methods includes plate and frame, crossflow and DE filtration.
Plate and frame or pad filter and DE filtration are less frequently used. They are depth filtration type. They waste wine as well a risking cardboard flavor at the beginning. Lenticular filtration also works well but the cost is quite height. These methods all produce a waste stream.
Crossflow, It is the most used, but are different types. It can recently do coarse filtration but do fine particles until 0,2μm so it’s basically reaching the « sterile » point (<0.25μm). The different membranes are ceramic, hollow fibre and spiral wound. It can great to also eliminate bacterias as botrytis, brettanomyces, etc as well as yeast. The machine is expensive, but the labour is not. Low waste, don’t get block, but it can strips the color off and there is no test to check if it is working.
The wine is almost done, let’s get it «sterile». Membrane filtration occurs as the wine is bottled. It is expensive but as crossflow got the most out, the filter most of the time lasts well. There is an integrity test to certify it is sterile. All this, provide microbially stable product.
You can find bottles of wine, who can have visible particles. Can be deformable particles as calcium crystal, after the bottle been forgotten in the freezer. Or it can be just a question of style. A study from UC David (AWRI 2017), show filtration 0.45um, has no consequence on the taste, and aroma. However a style more natural would skip the filtration, because the visual aspect it’s not always the priority. Some winemaker just want to avoid to move the wine too much.
NMIT – powerpoint CC410 filtration 2020