Answer: Unfortunately, I think you picked the cucumber too early. When saving cucumber seeds it is important to allow the cucumber (and the seeds) to fully ripen and mature on the vine. This means the cucumber turns yellow or brown depending on the variety and can take about five weeks longer than it takes to harvest a cucumber for eating.
Once the cucumber has matured, remove the seeds and pulp, put them in a glass or stainless steel container and allow them to ferment for about five days until the seeds sink to the bottom. Remove the pulp and rinse the seeds clean. Then spread them out to dry thoroughly. Store in a cool dry place such as in a closed container in the refrigerator.
As a final note, you should be aware that depending on the variety of cucumber you started with, the seeds may or may not be viable and any seedlings may or may not resemble the parents.
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