In the last 7 years of my life, I have been cooking most of what I eat, and preserving tomato paste (or tinned tomatoes) had always been a challenge for me. It wasn’t until November of 2013 that I found out how to preserve them.
Until recently, I would leave the unused paste in the glass jar, and pour some oil to cover the surface up to about 2 cm. Even with this method, the tomatoes will still go bad. Too many times I’ve had to throw away tomato paste because it got bad.
Then several months ago, I used some tomatoes and had half of the can unused. I put the remaining paste in a small yogurt cup (picture below) as I had lots of them lying around. To my surprise, 4 weeks later the paste was still there and not at all bad! Not even one spot of the white stuff that grows on it when it goes bad.
To be sure it wasn’t luck, I tried it again and same result. Since I started storing my tomato paste in little air-tight cups like this, they never ever went bad.