"Without refrigeration or canning, it [salt] was the only way to store most foods, other than drying."
Or smoking. Or potting.
ETA: unrelated to subject line, but from the same book. His description of beef and veal is just odd, in that he uses the word steer to mean an immature male. The book was published in the US, which makes this usage, if not wrong, at least terminally confusing. Worse, however, is this: "Because of the great cost of raising a male steer to maturity [which makes _no_ sense with his definition of steer, but might make sense under the US definition of steer, as castrated male], in most of Europe veal was the preferred meat." Well, actually, the real reason veal was consumed was because the cows were the valuable ones -- they produced more cows and milk and all its wondrous (albeit, sickening for me, personally) products. Male calves are, to quote Karen Hess, "supernumerary". Also known as, hey, we can eat that, and it's the only meat we're going to see for the next several months. "because veal cannot be easily preserved, it was almost always consumed fresh." Well, there was that whole, you've probably already eaten most of what you killed last fall and, again, you won't be seeing any more meat for a while. Further, the difficulty of preserving veal isn't about preserving veal at all -- it's about the sheer difficulty of keeping anything preserved through midsummer.
These things shouldn't be that complicated to understand and communicate.