As you must know by now, I always advocate for natural light in food photography. Its unique qualities enhance the colors and shapes of the food, and the combination of natural light with food just feels and looks right to me. But sometimes daylight is not reliable or available for a shoot and you have to switch to artificial lights. Maybe you have experimented with a table lamp or turned on extra lights in your kitchen, and if not, I encourage you to give your lights a try and study the resulting photos.
Most likely you'll find that you want more control over quantity, quality, and direction of the light. When I have to choose artificial lights I usually first go to fluorescent lights, but when I need more power, control, or portability, I turn to my speedlights. (Officially only Canon calls its line of hot shoe flashes speedlights, but it has become the catch-all term for small off camera flashes.) Since most food photography takes place on a small tabletop scene the power of these little flashes is all I need. Of course I could also turn to the big guns, strobes by Profotos, Broncolor, or Elinchrome, to name a few, but for a beginning food photographer small speedlights are probably the best place to start.
Diffuse and Diffuse Again
First thing, if you are trying to replicate natural light, do not put your flash on your camera's hot shoe! Instead, mount it on a lightstand to the side of your setup.
When you take a test shot you will see that the flash creates a very strong and harsh light. You can use an umbrella, bounce it off the wall, or as I did in my set-up, use a softbox to diffuse the light. If the light is still too harsh place a diffusion screen in front of the softbox for double diffusion.
Which Flash Should I Get?
Your next question is probably which flash you should use. Since each camera brand has different requirements I recommend you ask your local camera store for advice on which speed light is right for you. Personally, I stick to the top of the line Canon Speedlights, they are not cheap-- but they are precise, durable, and integrated with the rest of my Canon system. (To head off the camera-brand wars: I choose Canon gear because my mom shot with an AE-1. That’s all. Oh, and for full disclosure, I do own a Metz and a couple of Vivitar flashes too.)