Filtration Basics

Filtration is a process used to remove unwanted compounds from a hard cider. Those compounds can range from suspended solids that are relatively large to the smallest of particles like sugars and salts. Those smallest particles basically mean you will only have water remaining and would usually require an osmosis filter system. It is possible to over-filter. Given most of the filtration systems available to home and even professional craft cider makers, you probably don’t need to worry about putting cider in one end and getting water out of the other. That type of system would require some unique filters and system setup. But, it is good to understand the basics of filtration if you are considering using it. There are several affordable systems that home craft cider makers could employ. However, you may be wondering if you even need to filter.

Filtration is not a required step in making quality craft cider. It can offer some benefits that you might want to consider. If you enjoy a dry still cider, you can make some excellent offerings without ever thinking about filtration. If you start to use adjuncts, are seeking to make specific styles of cider, or even wonder how you can push your fruit to create better cider, filtration might be something to investigate. Broadly, I would put filtration into three categories.

  • Product Taste Enhancement: The use of filtration to improve the flavor or aroma. The goal is to enhance the quality by improving the taste.
  • Product Visual Enhancement: The use of filtration to improve the aesthetics of the hard cider. Your goal is to make it look better.
  • Stabilization: You are using filtration to remove compounds that might cause your cider to evolve and change. You desire it to be stabilize.

Let’s explore each of these in more depth.

Product Taste Enhancement

Filtration can impact the flavor of your cider. One key method of impacting flavor is by clarifying the juice you are fermenting. Yes, the clarity of your juice will impact the flavor. If you don’t believe me, test it yourself. I did a juice clarity test. This demonstrates how your processes can impact the the flavor of your cider. Clearer juice will generally create hard ciders that are fruitier. That is because suspended solids often harbor more micro-flora in the form of both yeast and bacteria. The solids also increase the nutrient level. These types of compounds tend to produce more phenolic aromas and flavors. These come from esters as well as fusel alcohols.

So, should your juice be sparkling clear before fermenting? No, you can filter too much as this strips the juice of needed nutrients. You want some suspended solids but using pectic enzyme, fining, and filtering to a nominal 5-10 micron level can result in fruitier ciders. Do you have to filter juice to create great cider? No. Will filtering your juice change the flavor of the cider? Most definitely. You will need to be the judge as to the benefits.

Product Visual Enhancement

Another important factor with filtration is the visual impact it provides. Simply put, filtration can remove suspended solids and some cloudiness. Note that some hazes, like protein haze, may be too small to remove with most filtration systems. They require special systems. You can use a plate filter system or an inline water-style filter (see photos below). The plate filter offers pads that go from coarse to sterile. The sterile will filter done to a nominal .045 microns. The water-style filters usually only go as small as 1 micron nominal. You can find 0.5 micron filters but they normally contain carbon, which can remove some of the aromas and other elements from your cider. You also need to flush them well or risk having carbon sediment in your cider. The key point I want to make is about the micron rating.

  • Pad Filter System: Used to clarify cider and remove yeast.
  • Inline Filter System: Used to clarify cider and remove yeast.

Most of these filters are sized based on a micron rating, which is the size of the opening or particles that it will block. The challenge is that these are generally nominal and it’s not often clear how effective they are at that rating. That means they can allow bigger particles to pass through. You can think of it as an average particle size. It gives you the approximate size of particle it can remove but it only removes a portion of those. Most filter membranes are also not uniform. Some holes are larger and some are smaller. The same is true for particles. A banana shaped particle or a long skinny one might be easier or harder to trap than a roundish particle. The importance of this is that a 1 micron filter doesn’t really remove everything over 1 micron in size unless the filter is rated in absolute. Most are not. This is why you often have to use filters rated lower to remove particles that are actually much bigger. Below is an adapted table from V.K. Joshi(1) on the size of various elements in cider. Removing suspended solids with filtration is generally straightforward. Removing proteins or other colloids, is not as simple and can require more sophisticated filtration system specializing in ultrafiltration or even reverse osmosis.

ElementMicron (Size)
Suspended Solids2-200
Yeast1-10
Bacteria0.5-1
Proteins, Tannins, Ethanol, and other aromatic compoundsAtomic Level (<0.1)
Adapted from V.K. Joshi and associates, Science and Technology of Fruit Wines: An Overview, 2017

Stabilization

The last category of filtration is for stabilization. This is about removing the elements from your hard cider that change how your cider matures or ages. These are generally the yeast and the bacteria, like lactic acid and acetic acid bacteria. This is needed if you want to avoid adding preservatives like potassium metabisulfite (Campden) and potassium sorbate or pasteurizing. These treatments are used to stabilize sweet ciders and prevent them from fermenting as well as preventing further maturation and potentially spoilage from undesirable yeast or bacteria activity. That means you need to remove particles that are 0.5 microns or larger. This usually requires multiple steps or you will plug up your filter.

You start at a coarse filter of 5-10 microns and work down to a sterile filter of 0.5 or less. Many filters can also contain compounds like carbon or diatomaceous that help inactivate or kill elements found in cider. It’s also important to remember that if you go to all the work of sanitizing your hard cider through filtration, you should work in a closed system if possible. Otherwise, you risk reintroducing those yeast and bacteria you just removed. The air and our environment is filled with these organisms and they can be introduced back into your cider if you don’t take basic precautions.

For me, this entails using kegs. Once my cider goes into a keg, I just move it from keg to keg to ultimately, bottles. My filter system installs between my kegs and I move my cider with CO2. I also keep my kegs sanitized and filled with CO2 so I minimize the exposure my cider can have to oxygen and the organisms that surround us. There are larger plate filter systems that include a pump. If you are doing larger volumes, this could be a good option but you will again want to ensure you minimize the exposure your cider has to non-sanitized equipment and the air. If you want to have sweet, clear, carbonated hard cider, investing in a kegging and filtration system can be an effective method.


(1) V.K. Joshi and associates, Science and Technology of Fruit Wines: An Overview, 2017

(2) )A. Alberti et al. / LWT – Food Science and Technology, 65, 2016


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