Why is it hard to ferment fennel? Fennel seemed like a natural for lacto-fermentation. 

There are many recipes with fennel as an ingredient (especially in cabbage kraut), but no one seemed to talk about just fermenting up a big ol' batch of fennel. 

So I gave it a spin using my standard brine: 3T kosher salt per quart plus bay leaves, peppercorns, and corriander. I ran one batch with two mason jars of fennel, and a second batch with three. 

Of the five jars, three turned out delicious but took a weirdly long time. I left the other two jars running for 5-6 weeks but they didn't show the active bubbling I expect and they never really came together. They were somewhat tart, but their pH was up around 5 instead of down in the 4's where it should have been. 

Is there some reason fennel doesn't want to ferment?
After dumping out a couple of jars of failed not-quite-fermented fennel I wondered, "Could fennel have antimicrobial properties?"

&lt;&lt; facepalm >>

Why, yes. Yes it could:


An article on PubMed
Another on PubMed
One on Science Direct
One on Research Gate


Granted, these are about the essential oil and not the whole plant. So I can't be sure this is the problem, but it seems very likely. 

Maybe a little fennel mixed in with something else won't muck up the fermentation process, whereas a whole jar of fennel can.

And though it's hard to know, I suppose there could be a safety concern. Lacto fermentation protects us through (1) salt, (2) oxygen depletion, and (3) acid production. Based on what I saw with the failed batches, (2) and (3) may have been below normal. If salt-tolerant critters were to survive... that could be bad.