Bacon opens the essay, "Of Studies," with this line:
Studies serve for delight, for ornament, and for ability.
This notion parallels the line quoted in your question. Those studies that delight are meant for private reading and personal contemplation, amusement, and insight. Those studies that are for ornament are used to improve discourse, speech, and writing. Those used for ability are used for the "judgment, and disputation of business." This is a simplistic interpretation of these first lines because this is the correct interpretation in the context of this essay. However, outside of this essay, I assume Bacon would agree that one can read for amusement or leisure but also reach a profound insight that could be used in serious learning.
So, those studies that delight would tend to be "books that are to be tasted." You don't really take in profound information; you simply taste it. There are no profound philosophical ideas that would require you to imbibe or swallow these ideas. Those studies that are swallowed are a bit deeper. They have more substance. They contain more wisdom than something light and amusing which would be used simply for tasting. The books that are to be chewed and digested have real philosophical, sociological, or psychological insights that become a part of your mental being. When you chew and digest something, you absorb the nutrients. Those nutrients become a part of you. Bacon is saying that only the most significant, truthful, useful, and worthy books should be chewed and digested. If they are superficial, practically useless, or lacking in truth, they should only be tasted.