Took 4 months to fix a fruit fly problem in my bokashi bin

I set up a bokashi bin under my sink in March and by week two it was crawling with fruit flies. I taped over the lid vents, which was a dumb first move because it made the bin smell like a swamp. Then I read that the flies were laying eggs in the top layer of scraps, so I started burying each new addition under an inch of finished soil. That slowed them down but didn't kill the cycle. What finally worked was freezing every banana peel and coffee ground for 24 hours before it went in the bin. Four months of fighting these little guys and the fix was my freezer the whole time. Anyone else have luck with a different method for keeping flies out of an indoor bin?