BLOG //
Karoliina Mäkelä //
Helsinki
// 28.1.2020

Filter Paper for Coffee: Size and Shape Matter

If you choose a brewing method and device that require filtering, you have basically three options: paper, metal and cloth. The most common option for filtering is filter papers. Filter papers come in different shapes, sizes and colour but what makes a good filter paper? Now let’s take a deeper look at the filter papers!

History 

Back in the day, Melitta Bentz wanted to get rid of the coffee grounds in her cup. As an innovative woman she tried different filtering methods and found out that paper worked the best. She patented the first version of her pour over filter and filter paper in 1908 and since then, many different variations have been created.    

first melitta filters and pour over
Picture: Melitta Zentralgesellschaft mbH & Co. KG

Shape

There are many different shapes the filter papers are manufactured in. 

  • V-shaped paper for modern versions of Mrs. Benz’s pour over filter and automatic brewers   
  • square shaped paper for Chemex 
  • round shaped paper for Aeropress, Chemex and some large urn brewers  
  • basket shaped paper for flat bottom pour over and automatic brewers 
  • filter paper roll for vending machines  

It is important to choose the correct shape but also the correct size for your filter. This way the paper fits perfectly to your device and enables balanced coffee extraction. Check out UC Davis Coffee Center’s publication about filter basket shape, if you want to know more about the effect of filter basket geometry on the sensory acceptance. 

different brewing methods and filter papers
Different brewing methods and devices require different filter papers.

Material   

There are numerous manufacturers, brands and versions of coffee filter papers. Also, the specialties per a paper type vary a lot. Some papers have special pores to optimize the flow and by that, the extraction. Some are thicker, as the Chemex paper, resulting to significantly clear, bright and light bodied brew. Then there is the big question: bleached or unbleached?  

Coffee lovers often say they don’t want to use bleached paper because the bleaching is bad for the environment. This might has been the situation back in the days but it is not the whole truth anymore.    

Chlorine gas based processing

  • Bleaching is done by elemental Chlorine. The word “elemental” is the keyword here as Chlorine in this form is the bad guy. Elemental Chlorine will join organic mass in sewage turning into toxic organic chlorine compounds. 
  • This used to be the main bleaching method but some of the cheapest filter papers are processed using this method to keep the end product price low. 
  • Might release additional flavor or odor to the coffee, the paper needs to be rinsed before use. 

Oxygen based process 

  • Totally Chlorine Free process (TCF). Bleaching is done by using Oxygen based radicals.
  • Does not release any additional flavor or odor, still it is good to rinse the filter paper before use. 
  • In addition to all the current filter papers are biologically purified, too. 

Chlorine Dioxide based method 

  • Elemental Chlorine Free process (ECF). Chorine is not used in the form of chemical element but as a chemical compound (chlorine dioxide). This is to avoid the chlorine to create any toxic organic compounds. 
  • Does not release any additional flavor or odor, still it is good to rinse the filter paper before use. 
  • In addition to bleaching, biologically purified.

Unbleached  

  • Mild off-flavor and/or odor. Always rinse the paper before use. 
  • As the total manufacturing process is lighter, the unbleached papers are a bit more environment friendly. The downside of lighter processing is that there is usually some wood fiber left in the end product. This might cause clogging the pores of the paper during the brew. That is why it is important to rinse the unbleached paper filter before use.  

Testing the difference

We brewed 6 batches of coffee using 1000 grams of water and 60 grams of coffee using Wilfa brewers. All the variables kept the same, only thing that changed was the filter paper material. We tested two low price products, one oxygen bleached and one unbleached. We also had four premium brand products, one bleached and three unbleached. Surprisingly, one of the low price products beat the expensive premium ones resulting to a clear cup and no off-flavor or odor. The bamboo-based caused an odd nuance and the one letting more oils through caused a dusty, clogged taste. Also, he low price unbleached resulted to a dusty cup as expected.

The results of the test:

  1. Low price, bleached  
  2. Premium, bleached, shorter contact time to get less bitter brew  
  3. Premium, unbleached, several perforated layers to optimize the brew
  4. Premium, unbleached, partially made of bamboo fiber, several perforated layers to optimize the brew
  5. Private label low price, unbleached
  6. Premium, unbleached, media lets through more oils for full flavor   
testing different filter papers
How we tested the different filter papers.

Essentials when using paper filter for coffee

  1. Ensure the size and shape are correct.
  2. If paper has a foldable side section, use it.   
  3. Rinse the paper carefully. 
  4. Remember to dump the rinsing water before starting the brew.  
barista brewing coffee in paulig kulma
Daniel brewing with Hario v60 in Paulig Kulma.

So if you want to use paper that is most environment friendly, choose unbleached. Just don’t do that because of the bleaching process itself, as it is not the harmful thing! And if you choose unbleached version, always rinse the paper and remember there will most probably be some off-flavors or odors.