Some varieties of smaller cucumbers are labeled "pickling" cucumbers because they are the perfect size to use for making whole pickles, such as dill. If you're making any type of sliced pickle, however, any type and size cucumber will do. The general rule is that the type of pickle you make determines what kind of cucumbers you use.
Not Peter Piper's Peppers
Pickling is an old food preservation system that uses the high acidity found in vinegar to prevent vegetables from spoiling. The vinegar kills any bacteria and imparts its tart flavor to the vegetables. While most vegetables can be pickled, cucumbers are the most common, and certain species have been developed just for that purpose. To be rated a pickling cucumber, the fruit must measure no more than 3 to 4 inches in length. This includes cucumbers labeled on seed packages as pickling and also as gherkins, very small cucumbers that are generally no more than 2 to 3 inches long.
Pickling cucumbers are designed to fit whole into jars, and their smaller size and thinner skins absorb the vinegar brine more readily than do larger cucumbers with thicker skins. Many old-time pickle recipes call for a substance called alum, which is added to the pre-soaking liquid to keep the cucumbers firm during the long-term processing of fermented pickles. This step is no longer necessary with today's shorter processes that keep pickles from becoming too saturated with liquid.
No matter what type of pickles you make, use only fresh, firm cucumbers that are as as free of blemishes as possible. Cucumbers that have started to go soft will only continue to deteriorate, particularly if you process them for long-term storage in a water bath, which essentially cooks the cucumbers. Wash the cucumbers thoroughly to remove any remaining spines and impurities, and slice or leave them whole in accordance with your pickling method.
The Inside Story
Pickling cucumbers contain less pulp by volume than larger slicing varieties, and their seeds are smaller and packed more closely together in the core. The skins of most varieties are bumpy and pale green, while the skins of long slicing varieties are a deeper green and smooth. Pickling cucumbers ripen sooner than standard varieties. Remember that all cucumbers should be picked before they ripen, either for eating fresh or for pickling. A fully ripe cucumber is overgrown, yellow or orange, with a bitter taste.