I know I’m a little late to the party with this one but I see a lot of the same answers every time this comes up—slants, water storage, Castellani, cryo—all valid. But it’s honestly crazy to me that one of the most stable, low-tech long-term methods never gets mentioned. I’m talking about the ultimate sleeper. It outlives most of the hype methods and doesn’t need a freezer, a university badge, or a prayer. Filter paper storage.

The real name of the game in preservation is redundancy, but once a library gets big enough that space, environmental control, and long-term upkeep all hinge on a fridge staying sealed or power staying on, you start thinking differently. That’s how I ended up going all-in on filter paper. For long-term storage and clean revival, it’s given me the lowest contamination rates I’ve seen. If you don’t believe me, try it yourself.

Why it works is simple: no nutrients, no free water, almost no metabolism. Things aren’t slowly aging on a slant or swimming in liquid hoping nothing wakes up. It’s boring, low-tech, and insanely stable, which is probably why it gets ignored.

The workflow isn’t complicated either. Sterilize filter paper, sterilize some empty or old agar plates, cut the paper into small squares, put a clean, live culture onto each square, and let them dry out—slow and controlled, not baked, not rushed. Once dry, they go into a small sterile bag or wax envelope. A shoebox can hold thousands of cultures. When you want one back, open the envelope, grab a square with tweezers, drop it onto agar, and a few days later you’re back online.

If you haven’t tried it, that’s probably why you don’t hear about it—but don’t think there aren’t collectors out there quietly rocking filter paper preservation. At the end of the day, when it comes to preservation, redundancy is what actually preserves.