This is the unsexy part of the winemaking process that, in all actuality, helps make the final product a bit more, well, sexy.
First, I want to clarify a few definitions that I know for myself, as a a consumer, can be quite confusing. On the back of a wine bottle or on a tech sheet you may have seen something like “bottled without fining or filtration.” Or, the opposite: “fined and filtered prior to bottling.” But, what does that even mean?
Fining requires adding a (fining) agent to the liquid that speeds up the “precipitation” of any suspended materials within. If you’ve ever made consumé, or have seen it made, you typically add egg whites, which gathers all the impurities in the liquid (usually leftover chicken/beef/whatever fat that swimming around there), which you can then skim off the top. The result is a clear broth, aka consumé.
Same thing with wine—there are microscopic particles (unstable colloids) floating around. Adding a fining agent (and, yes, you can use egg white here too), helps gathers those all together for removal. Although all agents will help clarify the wine, different agents can also target different impurities: unstable proteins; phenolics that could contribute to off-colors (ie: browning in white wines) or bitterness (ie: excessively harsh tannins in red wines); and those that remove color and off-odors.
Benefits: Clarifies the wine and stabilizes it against the formation of hazes later in the bottle.
Disadvantages: Over-fining is a thing. “Many fining agents can remove positive compounds from wine or make the wine unstable when too much is added.”
Key fining agents to know:
Fining agent that remove unstable proteins
1. Bentonite — A fining agent that removes unstable proteins. Bentonite is a form of clay that absorbs unstable proteins and unstable colloid coloring matter. It typically does not effect the flavor or texture of the wine but it can lead to some color loss in red wines. Luckily, it’s not necessary to remove proteins in red wine, as they bind with tannins, thus precipitate naturally and are removed when racking. It’s more important for white (and rosé wines) because these proteins can create a visible haze—not a cute visual for wine consumers. A disadvantage is that Bentonite can create a lot of sediment, so you lose wine volume when racking off.
Fining agents with own properties (ie: remove phenolics that could contribute to off-colors [ie: browning in white wines] or bitterness [ie: excessively harsh tannins in red wines]
NOTE: These can be used in conjunction with bentonite for their own properties and to avoid risk of over-fining (which in itself could make the wine unstable).
2. Egg white — This is the guy you want to use with your high-quality red wines, as it can remove harsh tannins and clarify the wine, but is a very gentle agent. Note: As an allergen, it must be listed on the label in the EU as well as other territories if present above a specified limit.
3. Gelatin — This protein collagen is extracted from pork. This is another agent you want playing on your red wine team, as it removes bitterness and astringency. It also plays well with white wines, removing browning. Note: It’s easy to over-fine with gelatin and a disadvantage is that it can strip flavor characteristics as well as create protein haze down the line. So, if using, it must be added in the smallest effective amount.
4. Casein — This guy’s made of milk protein and helps remove browning from white wine as well as helps clarify. (I guess that’s easy to remember because…milk is white?) Like eggs, milk-based things are considered allergens, so some regions will requite it to be listed on the label.
5. Isinglass — Fish bladder anyone? Well, supposedly this is a really effective way to clarify white wines and give them that star-bright visual quality. Like gelatin, it can potentially cause haze later down the line, so the smallest effective amount should be used. Oh, right, and it may smell fishy…
7. PVPP — Polyvinylpolypyrrolidone (Say that ten times fast with a mouthful of cheese and crackers…). This is plastic that supposedly removes browning and astringency from white wine that’s been oxidized. It’s said to be gentler than charcoal (below). It *can* reduce astringency and brighten the color of red wines as well, but it’s a less popular choice than those egg whites or even gelatin.
Fining agent that removes color and off-odors
8. Charcoal – This removes brown colors (FUN FACT: It’s used to create Pale Cream Sherry) and some off-odors. Like gelatin and isinglass, charcoal can over-fine easily thereby removing some desirable aromas and flavors as well. Bummer. Insider Trick: Avoid over-fining by treating one batch of affected wine and blending the result in with the rest. This will “reduce” the effect.
Filtration is the most common way to clarify wine. It is defined as the “physical separation technique used to eliminate solids from a suspension by passing it through a filter medium consisting of porous layers that trap solid particles, thus making the liquid clear.” So, kind of like passing that same batch of broth from above through a sieve or a cheese cloth.
The two (main) types of filtration are depth and surface.
The question above is specifically asking about surface filtration, as both membrane and cross-flow filters are types of surface filters.
How do these vary? Depth filtration traps particles in the “depth of the material” that forms the filter. (Fancy terminology, that.) As such, it can handle liquid with a high percentage of particles, like freshly pressed wine. Though depth filters don’t block very easily, it’s noted that it’s not absolute because if the filter’s been used for too long or if too much pressure is applied, stuff will get through. Like, if you’re passing that broth through that cheese cloth and squeeze super hard to get more liquid out, some of the veg pulp/chicken giblets/whatever is going to get into your soup.
Diatomaceous earth (DE) is the most common form of depth filtration. It’s formed using diatomaceous earth that, once processed, is pure silica and inert. It can filter very thick, cloudy wines and filter out a range of particle sizes and can do so oxidatively (as in a rotary vacuum filter) or inertly (in enclosed DE filters flushed with inert gas).
NOTE: Used DE must be disposed of responsibly, which adds an additional cost (and, side note, isn’t very environmentally friendly).
Sheet filters, or “plate and frame” filters simply allow wine to pass through a sheet of the filtering material. Common sense time: “The more sheets there are in the filter, the quicker the wine can be filtered because any portion of wine only passes through one sheet.”
Surface filtration simply stops particles that are bigger than the pore size of the filtration unit. (Think about the pore sizes on different kitchen sieves.) The two types are, as mentioned:
Membrane filters. These are slower than depth filters because the pore sizes are so tiny. (Fun Fact: often less than 1 micron.) So, it’s required that wine be pre-filtered (usually have gone through depth filtration) because the membrane filter will get blocked otherwise. As such, they’re usually used as the “final precaution” before bottling to ensure both clarity and microbiological stability. So, if you see something on a wine label or tech sheet that reads “sterile filtered,” that’s what that means.
Disadvantages: Though not an expensive piece of equipment to buy, the replacement cartridges are apparently expensive. I would add to this that the fact that you have to pre-filter before membrane-filtering would also add to time, labor, and cost which sounds like a disadvantage to me as well.
Cross-flow filters. This is kind of a handy piece of equipment because it self-cleans the surface of the filter as it’s filtering the wine. Unlike membrane filters, cross-flow filters can filter wine with a high load of particles quite quickly—no need to pre-depth-filter here.
Benefits: These guys, unlike the membrane filter, can handle wine with a high percentage of solids. It’s self-cleaning, so you don’t need to replace filter sheets, cartridges, or anything of that nature.
Disadvantages: It’s fancy. Therefore, it’s expensive. But, compared to the membrane filter, you don’t have to pre-filter before using this machine. So, depending on budget, it may be worth it to invest in a machine that does the whole job for you.
How do you feel about fining and filtration of your wines? Does it strip away unique character of the wine? Or does removing excess solids allow for better fruit and terroir expression? Thoughts? Let me know! And thanks again as always for studying with me!
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