Here's the scenario--you're going to someone's house where you're likely to be pressed into service in the kitchen, and you know they don't have a decent knife in the house, but you don't want to be so presumptuous or it's otherwise inconvenient to carry a knife roll. Or maybe you're going away for a weekend where you'll be cooking and you want to travel light. Of course one can always make do with what's there, but maybe there's an alternative--a folding kitchen knife.
I proposed this query to my friends on the eGullet food forum, and we came up with various ideas, but there seem to be three real, full-sized, multi-purpose folding kitchen knives out there, all in the style of the Japanese santuko, a knife of relatively modern design, the name of which means "three virtues"--slicing, dicing, and mincing--as opposed to the more specialized traditional japanese knives like the usuba for slicing vegetables or the long yanagi sashimi slicing knife.
There are some inherent design limitations in a folding kitchen knife. To be practical, the blade will be about 4-5 inches at most, and to fold properly, the handle has to be longer than the blade and the end of the handle has to come about level to the edge of the blade, meaning it must be used at the edge of the cutting board or with a small cutting board, or the end of the handle will hit the board before the knife completes its arc. The long handle also creates a balance problem, since the handle is usually shorter than the blade, and one normally wants the balance point to be around the spot where the heel of the blade meets the handle.
The knives we came up with on eGullet were the A.G. Russell Hocho, the Ryback Folder, and the beautiful Maruyoshi folding santuko. There was one very avid user of the Russell Hocho which is the least expensive of the three at around $65 and is the longest in production, but based on the photos, I liked the design of the other two. One poster bought the Maruyoshi, which has a nice wooden handle and beautiful handmade damascus blade, but it was the most expensive at about $250 from Japan Woodworker in California, and seems more to suit people who like to hold the knife with a pinch grip rather than my preferred hammer grip, which I think is better suited to a knife with a short blade.
I settled on the Ryback folder for about $100 shipped from Germany to the U.S., because I liked the fit and finish based on the photos, and the real article lives up to the photos. It also comes with a handy padded cordura pouch.
The frame lock mechanism, above, is very sturdy, but beware that there is a detente before the knife is fully open, and it is necessary to open the knife fully for the lock to be engaged.
The blade is 1-7/8 inches wide, which is wider than my Wusthof santuko shown above, and 4.5 inches long with about 4-3/8 inches of usable cutting edge. Full length from handle to tip is about 10-3/4 inches.
Out of the box the edge is comparable to the factory edge of a decent German knife, but I've come to like a finer edge, so I've made it sharper using my Japanese whetstones.
I've been using the Ryback for everything for a few days, and I've gotten used to the balance, but I still prefer my fixed blade knives given the choice. Watch the video above, though, and think about the last time you made a meal in a vacation condo with whatever dull steak knife they had in the drawer. Wouldn't this have been better? The blade holds a fine edge very nicely, and it's a real, functional kitchen knife that works like a chef's knife or a santuko.