Often recipes say to chop garlic, but I usually cheat and just crush it as it's quicker. Is there any difference in doing this? Will it have much of an effect on the flavour of the dish?
I guess it depends upon the definition of "crushed" If by crushed, you mean using a garlic press, then there is quite a difference between chopped and crushed garlic. When you crush garlic, no need for a garlic press, the flat of a knife and a little salt is all that's needed, you release the essential oils, resulting in a stronger flavour. You can also purée the garlic.
It's also important to consider the type of recipe, in some recipes, such as a pasta sauce, chopped garlic is fine. In Asian cooking, especially Indian cuisine, it's common practice to use minced or puréed garlic. In roast dishes, using the whole cloves in the roasting tin with the meat, can produce an incredible sauce.
Chopped and crushed garlic have different flavors in dishes. The smaller the pieces the garlic is made into (with crushed being super small), the more pungent and bitter the flavors. Several food bloggers have reported their experiments on testing the differences.
This sounds surprising, but members of the Allium genus (which includes garlic, onion, leek ...) are booby trapped: around the cells there is a liquid that when combined with a chemical from the cell's interior creates a series of nasty sulfur compounds. The more the cells are damaged and exposed to oxygen by cutting or crushing, the more of these sulfur compounds are generated.
If the garlic is fried, the size of the pieces also determines how much of it browns. For crushed garlic this can happen before one has a chance to add more liquid to the dish, essentially burning the garlic and imparting a bitter taste to the dish.
I find some difference. It's not so much taste as appropriateness for use in the dish.
You get slightly more taste out of crushed garlic (by which I assume you mean crushed in a garlic press). But this is only as a result of the surface area and also the fact that there's more of the juice is released - it tends to be wetter. However it tends to burn quicker as the individual components are smaller.
Therefore I find that crushed garlic is better in recipes where you cook briefly or add at the end for the stronger raw garlic taste.
Chopped garlic is better for recipes where you're just using it to accentuate a flavour - along with onions or shallots. Because it's bigger it takes longer to cook as well (not by much mind).
For salads, you'd want to use crushed garlic, actually i find for any dish that is serves raw garlic, has to have it super duper minced/pureed. Biting on a small piece of garlic usually leaves a bit of a bitter taste.
in cooking, if you're sauteeing, then the garlic has to be a bit finely minced / chopped so it doesn't burn as easily if it were pureed
in roasting, slow cooking methods, low temperature cooking, that you want to have large chunks of garlic as that'll be the only way to extract all the flavors out of the darn thing
I'm hoping you know the knife trick, where you put the garlic between the cutting board and the broad side of a knife, and then POW: crushed garlic. A little hit for bigger chunks, a big hit for pulverization. A quick dice afterwards for really fine results.
I like adding garlic closer to the end, which isn't the traditional way of treating it as an aromatic. It imparts a lot more flavor, and if you have good garlic, it works great. But I like garlic a lot.
Chop garlic if you're frying it, crush garlic if you're adding it to a wet sauce or mixture.
For example, I prefer to cook a Chili by frying the minced meat first and adding the garlic later - crushed garlic works well for this. However if I'm softening onions and adding garlic chopped works best.