Wine Filtration - Depth vs. Cross-flow

Posted October 30, 2014

 

The main concerns when discussing wine filtration are time, labor, cost, and wine quality. Let's compare  depth filters, and cross-flow filters in regards to each.


Labor

Filtration is a crucial stage in the winemaking process when desired. It's no surprise that most filtration processes require trained staff for proper operation. With depth filtration, the need for trained operators decreases as you move from pressure-leaf to plate & frame to lenticular filters. For example, pressure-leaf filters need someone who is adept at handling DE properly (or the alternative filter medium used), knowledge of how to properly create a filtration cake inside the drum (a failed cake is not only a waste of money and time, but really embarrassing), and the pressures involved in maintaining a good filtration run. Lenticular filters just need someone who can clean the machine properly (making sure the paper-like scent associated with pads and discs is removed) and make sure the pressures are set properly. With all depth filtration, the trickiest part for the operator is knowing if and when to make the call to stop a filter run and switch out the filter medium.

Cross-flow filtration is much more complicated technology, but the units are rather simple to operate. Most cross-flow units have an automatic cleaning cycle that only requires chemical preparation and pressing a few buttons. Basic parameters must be set for filtering, but then the machine pretty much does the rest on its own.


Time

This is something not many winemakers have. Cross-flow filters are definitely a time-saver because they usually run at high flow rates compared to depth filters. A filtration run that may take an entire day with a plate & frame filter will probably only take a few hours with a cross-flow.

Remember those commercials with the 'set it and forget it' catch line? That's cross-flow technology. It's easy to setup, clean, and start running a cross-flow. Once you do, the machine does almost everything else itself. Depending on how automated the machine, some cross-flow filters can be left alone filtering overnight. When the source tank is empty, the unit will evacuate itself, close all valves, and clean itself.

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Cross-flow units usually have a 0.2 micron nominal porosity. Many would argue this as a negative, since many winemakers like having the option to coarse filter wines. For those that want this level of filtration, cross-flow is the obvious choice. One filtration pass can take dirty wines to bottle-ready. When I say 'dirty', I'm not only referring to microbially but also those wines containing heavy sediments, such as cold-stabilized whites or reds straight from the barrel.

With depth filtration, filtering to sterile (0.45 micron or lower) with one filtration pass is nearly impossible. This is particularly true with larger volumes of wine. A plate & frame filter with a crossover plate is probably the best bet, but good luck getting an early-release Marlborough Sauvignon Blanc through.


Cost

Plate & 

The price tag is one of the biggest deterrents of the cross-flow filter. A small single membrane cross-flow has a $20,000-25,000 USD base price. More membranes are needed for more throughput of wine, and the price increases steadily with the number of membranes, size of the unit, and the amount of automation involved.

The most common plate & frame filters are 20-plate. A unit like this costs around $6,000-7,000 USD, which is about the same for a lenticular filter with the equivalent filter surface area. The equivalent sized cross-flow would likely be a 3-membrane unit with a base price around $45,000-50,000 USD. 

Sounds like cross-flows are WAY more expensive? Not necessarily.

Much of the base price for a cross-flow unit is the membrane(s). These membranes rarely, if ever, need replacing. There are also labor and time expense savings that can prove cost-efficient.

Depending on the type of depth filter, filter medium can range from $50-600 or more per filtration run. You also need to deal with the disposal of this filter medium, something that is a constant headache for wineries using pressure-leaf units. The waste produced from depth filtration is also a concern in terms of the 'go green' initiative that many wineries are pushing.


Quality

This is the most important aspect in my opinion. It is also the aspect I will give the least information about as it's such a subjective matter. Every winemaker has a different opinion whether filtering or not is desirable. More so, what level of filtration is ideal for different grape varieties and wine styles.

The information above may make it sound like I am all for cross-flow filtration. I'm not.

I think it's a very viable option and one that works exceptionally well in a myriad of situations. Nevertheless, I have produced plenty of unfiltered wines and very lightly filtered wines over the years. My main concern with cross-flow technology is the fact that it has a nominal porosity. It can't be adjusted to do coarse filtering like depth filters can. The amount of filtration desired is usually a stylistic decision, but just as often may be a precaution as mentioned in my previous article. 


If a winery wants to sterile filter their wines, cross-flow is definitely the best option. Otherwise, depth filtration is really the only choice.