Syringe Filters

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Use 0.22μm sterile PTFE syringe filters

You can potentially replace the PTFE material with Nylon, however there appears to be less data indicating safety, and this should require more research.

PTFE is safe with oil, benzyl alcohol, and benzyl benzoate¹ ².

Details (for sterilization)

Pore Size: 0.22μm (this size is required for sterilization)
Sterility: Use pre-packaged, sterile filters.
Size: if you’re filtering 1-10mL, use a 13mm filter. 10-100mL use a 25mm filter³. 100m-250mL use a 33mm filter⁴. Larger is generally easier to push though.
Filter material: Polytetrafluoroethylene (PTFE). Nylon filters may work, but require more research to verify.
Hydrophobic or Hydrophilic: Inconsequential for an oil-based solution.

Details (for pre-filtration)

Pore Size: 0.45μm
Sterility: not required
Size: if you’re filtering 1-10mL, use a 13mm filter. 10-100mL use a 25mm filter³. 100m-250mL use a 33mm filter⁴. Larger is generally easier to push though.
Filter material: Polytetrafluoroethylene (PTFE). Nylon filters may work, but require more research to verify.
Hydrophobic or Hydrophilic: Inconsequential for an oil-based solution.

Don’t use PVDF of PAS

Benzyl benzoate, an ingredient in the brew, can cause PVDF filters to dissolve. This could have potential side effects such as filters breaking or PVDF leeching into the filtered solution. There is minimal data to support whether PVDF is safe, so in this case it’s best to air on the side of caution⁵.

Bubble Point

Many, but not all, filters will list a bubble point or “max burst pressure”. Check or confirm this bubble point by testing the bubble point of your filters with a sample of your solution. Bubble points can change when the filters are pre-wetted with different solutions, so always check with your actual brew.

Read more about bubble point testing here.

Cheap Filters vs High Quality Filters

There are many filters available in small 10 packs on websites like Amazon. While these filters are economical they are of substantially lower quality.

	Amazon/eBay/etc Filters	High Quality Filters
Cost per	$1.30 each	$2.00 each
Pack Size	10	100
Total Cost	$13	$200
Bubble Point	Variable 30-45psi	Consistent 50psi
Filter Speed	80-120 seconds per 1mL	15-30 seconds per 1mL

If you can afford the upfront cost of higher quality filters they make a massive difference. This makes less sense for those following the small or medium guides.

Opinion: I have a theory about these filters which I can’t prove without a microscope or something. Lower Quality (LQ) filters likely have inconsistent pore sizes on the filter surface + less stable filter surface, while Higher Quality (HQ) filters likely have an extremely consistent pores on the filter surface with strong stability. I believe this for a few reasons. First, from a purely economical standpoint, an Amazon seller has less incentive to make a high quality product compared to a company who’s whole business is manufacturing filters. Second is the variable bubble point. On an LQ filter, I might get a bubble point of 45psi, and then push 20mL of product though it, then suddenly start getting 30psi bubble point. To me this indicates that it degraded while it was being used. HQ filters on the other hand will always come back with a consistent 50psi when I’m using them in a normal way. Finally, during the bubble point test itself, LQ filters put off a stream of bubbles about 0.5mm in size, where as HQ filters are putting out something more akin to foam, which is bubbles more on the scale of 0.05mm each. Why would LQ filters release air bubbles almost 10x the size of HQ filters? To me this points back to the quality of the filter itself, the HQ filters may have more consistent pore sizes and may be letting smaller pockets of air through at once.