We turned to expert Linda Ziedrich, author of "The Joy of Jams, Jellies, and Other Sweet Preserves: 200 Classic and Contemporary Recipes Showcasing the Fabulous Flavors of Fresh Fruits," to teach us what errors can be fixed, what can’t, and how to avoid some common rookie mistakes. 

What went wrong: The jelly boiled over.

What happened/what to do: Pretty elementary — your pot is too small. Before starting, check your ingredients to guesstimate the size pot you need. In this case, bigger is always the safer bet. Same goes for your canner. You need at least 1 inch of water above the jars when processing, and another inch of space for boiling room. 

What went wrong: The jelly just won’t "gel" up — even at the right temperature. 

What happened/what to do: Don’t panic — there are a few things you can try. "When gelling doesn't happen, there may not be enough acid; if this seems to be the case, you add more lemon juice," Ziedrich says. "Or maybe the fruit was overripe or even old, in which case you need to add commercial or homemade pectin." If you’ve already added commercial pectin and it still won’t gel, chances are your pectin was old and degraded — make sure to check expiration dates before using. 

What went wrong: The jam or jelly tests as gelled, but then doesn’t thicken in the jars. 

What happened/what to do: The best thing to do in this situation is wait. “Some fruits take as long as three days to gel,” Ziedrich says. If even then your jam isn’t setting, you can un-jar it and go back to step one. Make sure to clean and sanitize the jars before reusing them. 

What went wrong: The jars won’t seal — the center of the lid pops when you press on it. 

What happened/what to do: There’s a good chance the jar has a nick on the rim, preventing the seal. Open the jars and check for nicks. If you find them, you’ll need new jars. You also may have gotten some jam or a seed stuck between the rim and the jar, which is also preventing the seal. If you're sure there is no nick or chip on the rim, try again with new lids and start the jars in warm water instead of boiling to allow everything to get up to temperature. If you can’t be bothered, just keep this jam or jelly jar in the fridge and eat it first.

What went wrong: The surface of the jam or jelly turned dark. 

What happened/what to do: There was too much headspace — the space between the jam and the lid. Even with boiling water processing, "you don’t get all the air out of the jar, and you can get oxidation," Ziedrich says, which causes the top to turn a dark color. It’s not toxic, so you can scoop off the top layer and enjoy the rest of the jam. For next time, make sure you have 1/4-inch of headspace for jams and jellies. Less than that, and it can overflow and spill over — preventing a seal. 

What went wrong: Mold has grown on the jam or jelly.

What happened/what to do: Your safest bet: don’t eat it. Even if you think you can scrape it off and eat what remains, the mold has likely contaminated the whole jar. Mold generally grows in jam when they're not sealed correctly or not processed in boiling water long enough. 

What went wrong: The jam is discolored or lightened. 

What happened/what to do: Most likely you stored the jam in an area that was exposed to sunlight or was too warm. Store your jars in a cool dark area for best results. 

What went wrong: The jam is cloudy. 

What happened/what to do: There are several possible causes for cloudy jam. Either the juice wasn’t strained correctly or there was too much pectin. If you squeeze the jelly bag while straining, the pulp will be forced through, making the jelly cloudy. Also, too much pectin, caused from either using very underripe fruit, or adding too much commercial pectin, means that the jelly sets too fast, and air bubbles don’t have a chance to rise to the top. A third cause is letting the jelly cool too much before pouring into the jar. There is no fix for cloudy jelly, but it's safe to eat.