Michigan State University Extension
Preserving Food Safely - 01600560
Fermented pickles require more time and effort to make than fresh-pack pickles. Brined dill pickles are an example of fermented pickles that are prepared by soaking cucumbers in brine (salt water) for about 3 weeks. During this time, lactic acid bacteria--which are naturally present on cucumbers--convert sugars in the cucumbers into lactic acid. Lactic acid not only preserves the pickles but also gives them good flavor. (Vinegar, which contains acetic acid, gives fresh-pack pickles a "sharper" flavor.)
When making the brine, measure the salt and water carefully. It is important to get just the right concentration of salt so the lactic acid bacteria--which can tolerate salt--will be able to grow. Most spoilage organisms cannot tolerate salt and will die in the brine. If the brine is too salty, even the lactic acid bacteria will die. If the brine is not salty enough, undesirable organisms will grow and spoil the pickles.
Make the brine with cold or room temperature water. Do not use boiling water--it will kill the lactic acid bacteria. During fermentation, keep the pickles at room temperature between 68 and 78 degrees Fahrenheit.
Fermenting pickles must be kept submerged. Uncovered pickles will spoil. Use a plate to cover the pickles and weight it down with a glass jar or plastic bags filled with brine (6 tablespoons salt to 1 gallon of water). Remove any scum which forms on the surface of the brine daily. The scum consists of yeasts which destroy lactic acid and produce enzymes that make pickles soft. If the scum is not removed daily, pickles will spoil.
After three or more weeks, fermentation should be complete. Pickles will have an olive-green color and a desirable flavor. The brine will be cloudy as a result of yeast growth during the fermentation period. Strain the brine, then heat it to boiling. Pack the pickles into clean, hot jars. Do not wedge tightly. Cover with boiling hot brine. Put lids on the jars and process in a boiling-water bath.