I plan on making blood orange marmalade. The recipe calls for pectin, but I don't have any. Can I make it without pectin? Will it still gel? Will leaving out the pectin change the taste?
You can make your marmalade without the pectin. The flavor won't be affected and it should still gel up fine. Here's a 3-citrus marmalade recipe without pectin if you want to compare
Most pectin is produced from oranges, which have a naturally occurring high pectin content (a side note, the process is a highly un-friendly environmental process). My mum has made marmalade forever and has never used pectin and it always is set perfectly. Try mixing the sugar and peels over night to help macerate the peels, which will release the pectin more readily (old jam makers trick).
I make citrus marmalade without pectin, and it turns out great. You might want to look around for another recipe. Some of them recommend tying up a cheesecloth bag with extra pith, seeds, and membranes, as that's where a lot of the natural pectin is. I've never done that, but I am sure to include pith. As for your "will it change the taste" question, the reason I prefer jams without added pectin is that they generally have smaller amounts of sugar. It's a personal preference.
I never use pectin when I make marmalade. I use Madeline Bullwinkle's process for making any citrus marmalade:
Day 1 - Remove the colored part of the peel and chop into whatever size bits you like your marmalade peel to be. Remove and discard pith, chop fruit, and measure peel and fruit. Place in a bowl with an equivalent amount of water. Cover and let sit overnight.
Day 2 - Bring mixture to boil, reduce to simmer and simmer 15 minutes. Turn off heat and let sit overnight, covered.
Day 3 - measure mixture, bring to a boil, add equivalent amount of sugar (actually, I cut it to between half and three-quarters of the equivalent amount), return to boil and bring to the gel point (8 degrees above boiling), which will take about 10 minutes. Believe me, it will set up nicely!
As everyone has indicated, citrus is high in natural pectin, so no added pectin should be required. Typically, added pectin also requires more sugar than a recipe without (the pectin itself requires more sugar to set properly). There are two advantages to added pectin: it has an almost 100% certainty of setting, and will do so much quicker than without. The advantages of no added pectin: less sugar (so a better fruit taste) and no need to go find pectin. Disadvantage to no added pectin: you need to make sure your product gels (8 degrees above boiling, i.e., 220 is one possibility) and your product will have to cook much longer, which can create a "cooked fruit" taste. I've made a ton of jams/jellies in my life, but only a few marmalades. From the jam/jelly world, I can tell you that 220 works "most of the time", but the frozen plate trick is actually much more reliable (place a plate in freezer -- when you think your product is set, place a small amount on frozen plate, let cool about 1-2 minutes, and drag your finger through it. If it puddles back together, it is NOT set; if it stays in two separate sections it is set). And, actually, a marmalade/jam/jelly that doesn't set isn't the end of the world -- it is still great syrup to be used to flavor morning yogurt, poured on ice cream, or even in a cocktail...
I agree with Sea Jambon about the plate test - it seems very difficult to find an accurate enough candy thermometer for the purpose, so even though I put mine on the edge of my jam pan, I still use the plate test and trust it more than what the thermometer reads.
I learned about the seeds in the cheese cloth bag a few days ago but I haven't tried it yet.Apparently,you can use seeds from any citric fruit(lime,lemon,orange,grapefruit,mandarin)and if you're using the fruit on another preparation you can save the seeds wrapped in aluminum foil in the freezer.