The most curious thing happens when you pan fry old, crushed garlic cloves. They turn blue-green. Like, fluoro bright blue.
Though it might seem like reason for alarm, your dish isn't ruined. Without getting too scientific, it's a reaction that occurs when compounds which started out safely locked away within the clove are exposed and react with enzymes. The same things happens when garlic is pickled (and it can also occur to onions). It's still completely fine to use and safe to eat.
Though Ben Varela, Group Executive Chef at Public House Management Group, recommends that you go for fresh garlic wherever possible.
"When it comes to garlic, fresh tastes the best. Especially with Australian garlic. We've got the best, most amazing garlic in Australia. There's also a lot of stuff that's imported from China, and generally the peeled garlic is imported, and not as good," Varela said.
"There are garlics that have a purple shade on the outside, and they are a different variety of garlic. That's my favourite, actually, and it's an Australian product. The flavour is nice and not too strong. The white garlic tends to be stronger and sometimes has an acidic taste, whereas the purple coloured garlic has a smooth flavour. If you roasted it on its own you could eat it by itself."
If you're not sure of the age of the garlic you have at home, check for little green sprouts.
"If you ever notice that your garlic starts to sprout green shoots, that's an indication that it's not fresh. It's not all bad, it's still got life in it, but it's not ideal," Varela said.
And when it comes to cooking with garlic, how much to use is a very personal thing -- though it's better to err on the side of caution (the people around you will thank you).
"As a general guide, half a glove per person is a good measure to go buy."
Lastly, instead of just chucking the leftover cloves in the door of the fridge, make a garlic paste instead. No more sprouty cloves.
"Garlic is best kept in the fridge, but if you're not going to use it all in the one go, the best thing you can do is put it through the food processor, then add some olive oil. You've then got a garlic paste that's always ready to go and it'll last longer. A teaspoon would be worth roughly a clove," Varela said.
