Kitchen Mysteries is a weekly exploration of oddities surrounding cooking and food. They could be recipes that fail when they shouldn't, conflicting advice from different sources, or just plain weirdness. If it happens in a kitchen, and you're not sure why, send a tweet to The Food Geek to find out what's happening.
CooksBakesBooks asks via twitter:
Strictly speaking, no. The sprout is not a a source of the bad flavor, but it is indicative of the flavor. Before being cooked or preserved, vegetables are alive. Even garlic. A garlic is a bulb, much like a tulip bulb, but presumably tastier. If you want to grow some more garlic, you plant it in the ground and the sprout that forms develops into a new plant, gathering energy for the next growth spurt when new garlics bulbs are made.
In order to grow, plants need energy and nutrients. Different plants go about this in different ways. Some store a little energy in seeds, enough food to, under the right circumstances, kick-start the growing until nutrients can be pulled in from the earth and sky. With little seeds, the plant's strategy is usually one of numbers: send off many, many seeds, and hopefully at least a few will reach the proper conditions for growth. The ones that don't make it haven't used up that much of the original plant's energy. The ones that do, continue to become plants of their own.
In the case of bulbs, the plants go with an alternate strategy of putting a lot of starting energy into the plants, and giving them a good chance for survival in exchange for reducing the number of bulbs that are produced when compared with the little seeds. These bulbs do not require the ideal conditions to start growing, because there is so much goodness packed inside the bulb. Consequently, they start growing when conditions are only vaguely ideal for them.
Generally, these "vaguely ideal conditions" seem to be inside your kitchen, roughly 10 minutes after taking them out of the bag. When they start to sprout, the visible indication is the little green sprout coming out of the top of the clove. That's not all that happens, though. Remember that, in order to grow, the plant needs energy. The energy is coming from the very clove that the sprout is, er, sprouting from.
Garlic has something of a sweet flavor when it's fresh. Sugar makes food sweet, and it also provides energy. As the garlic sprouts, that sugar is used up, among other chemical changes necessary to create the sprout and prepare for even bigger growth. The upshot of this is that not only does the garlic lose its sweetness, but it becomes bitter as well. The bitterness is not because of the sprout, as I mentioned earlier, the sprout is merely a visual indicator of what's happening underneath.
The best way to avoid the problem is to prevent the garlic from sprouting in the first place. First, pick a fresh garlic from the store. Avoid anything with sprouts coming out of it, naturally. Skip anything with too much of a papery skin, and always buy garlic that is heavy for its size. Heavy garlic means lots of water inside, which means it's fresh.
When you have it home, remember three things: dark, dry, and cool. Lack of external water, light, and heat indicate to the bulb that there's no reason to start a growth spurt, so your garlic can retain its flavor for quite a while. Potentially months, though I tend to start looking for new garlic after a couple of weeks because, well, I prefer fresh garlic.
If the garlic does start to sprout, all is not lost. If you let it grow, you have garlic scapes, which are tasty additions to any food that you would eat with garlic. You can read more about using garlic scapes, and I've found that it's hard to wander the internet these days without tripping over at least a few garlic scape posts a day.