Call us old-school, but we proof our yeast even if it's not mentioned in the instructions and even if the jar of yeast says it can be added right into the dough. We just don't want to go through all the trouble of kneading our dough and anticipating a gorgeous loaf if the yeast ends up being a dud! Here's how we do it:
The idea of proofing yeast originally came about as a way of "proving" that the yeast was still active. This was back in the days when yeast had a lot shorter shelf-life and bakers couldn't always be sure their yeast was still good. Nowadays, yeast can be refrigerated or frozen for about a year and still work just fine. But unless you're baking every day, we still think proofing is a good idea - better safe than sorry!
All you do is measure out the yeast and mix it with the water called for in the recipe. Yeast is happiest at about 75°-80°, so the water should feel barely warm or lukewarm to the touch. Add just a pinch of sugar to give the yeast something to munch on.
Let the yeast and water sit for a few minutes. First, the water will dissolve the dry coating around the granules of yeast, releasing the active yeast inside. The active yeast will go to work on the sugar and a bubbly foam will start to form on the surface from the carbon dioxide being released. This foam is proof that the yeast is active, and once you see it, you can add the yeast to your bread dough.
Do you think proofing yeast is important, or are we just being superstitious?
Related: Food Science: What is Sourdough?
(Image: Emma Christensen for the Kitchn)
How to Bake a Potato: Three Easy Methods
How To Cook Tender, Chewy Wheat Berries on the Stovetop
Good Food to Share 
The Big Book of Small, Cool Spaces 
Apartment Therapy Presents 
The Eight-Step Home Cure 
Straw Mat from The ...
10 No-Fail Decor Tricks & Tips for Small Spaces
Beth's Romantic & Retro Residence
Can baking powder be proofed too?
I never proof yeast anymore.
I have been using SAF-Instant yeast (it's only about $3 for one of those brick type sealed bags, probably just under a pound. GFS carries it.) for years and it never fails. I make bread about 3-4 times a week so I use the yeast up pretty quickly. When the yeast jar gets about 1/4 full I buy more and have never had a problem.
Even if you use it occasionally, SAF Instant yeast is a bargain compared to the price of those little packets in the supermarket.
Pixie,
Baking powder does not get proofed, but if it is too old it won't work very well.
I always proof my yeast!
...of course I use it more for making my own beer than I do for bread.
I think it's an unnecessary step. Like melkozek, I use SAF instant, which does not require proofing. Neither does fresh yeast.
As far as baking powder, here's an interesting experiment.
melkozek - I figured it doesn't work well if too old, but there's no way to test it ahead of time before actually baking with it? I've recently baked a couple of times with some baking powder I've had for an indeterminate amount of time and I'm not sure if it's working or if it the recipe is coming out as it actually should.
Baking powder is baking soda and some sort of acid. One way to test the potency of the baking soda in baking powder is to add some acid to it, like vinegar or buttermilk and look for effervescence. Usually baking powder loses potency after a year or so, depending on how it was kept.
I third the SAF recommendation. It works amazingly well, 110 percent of the time - no need for proofing. I had not seen it in our stores in Nashville but found it online through King Arthur.
I proof when using Active Dry Yeast. Don't proof when using Instant. No problems yet.
I never proof yeast. And I don't by it from the grocery store either. I buy the 3lb packages of RedStar from CostCo and keep it in the freezer.
I'm with Melkozek too; I use SAF Instant, bought in one-pound blocks, and kept in the freezer. It'll last at least a year, and it's not hard to use that much if you bake much bread at all.
I used to be an active-dry, proof-it-every-time kind of girl, but I've changed my tune. It's so much faster to just whisk instant yeast in, and not have to worry about whether or not my water is the right temperature. Instant yeast is a hardier strain, and can withstand liquid temperatures up to about 130 degrees F (assuming it's been whisked into the flour). Anything cooler than that is just fine, even ice-cold liquid.
I'm not going to condemn anyone for wanting the extra reassurance of proofing yeast, but if you use quality instant yeast, there's really no need these days.
A Bread A Day
I never proof my yeast. I have kept a jar of yeast in the freezer well over a year without any noticable ill effects.
Yeast does not suddenly up and die - it will sort of fade gradually, so if you find that your bread is not rising as fast as usual, you might want to think about replacing the yeast.
I also use much less yeast than recipes call for - never more than tsp per cup of liquid and sometimes less, unless the recipe has a lot of eggs and butter.
But I have a friend for whom proofing the yeast is part of the ritual of making bread, and I can't argue with that.
Oh, I meant to say that with active dry (non-instant) yeast the reason you proof is mostly because you need to dissolve the little yeasticles and start them growing before mixing them with everything else - Active dry yeast is formulated in such a way that just mixing them into the flour doesn't work well. But with instant yeast there really is no practical reason to proof.
Pixie, to test your baking powder for freshness, try dissolving 1 tsp. of the powder in 1/4 cup of hot water. It should bubble quite a bit. The less it bubbles, the less effective it's going to be. Good idea for a post!
bubble and sjbreeze - thanks! I'm going to test my can of baking powder - I think my muffins didn't rise enough because it's old.
I think proofing is important. I made cinnamon rolls last weekend, I didn't take the time to proof the yeast and I was disappointed. It's worth it to take a few moments to be sure. Even if you buy new yeast, you can't know for sure how long it has been on the shelf at the store.
I'm coming in late like splendid market. lol! I'm not going to say whether or not it's needed, what I want to know is what do you do with refrigerated yeast?
The picture you have there is the kind that if you don't use it all (which there is no way you would unless you own a bakery), then you need to refrigerate it. So how does that affect the proofing with water temperature? Shouldn't the water be hotter? Or should you let the yeast sit out for a time before proofing?
Oh and @splendid-market, I don't think it matters how long it has been on the shelf. What matters is the date stamp on the yeast.
I tried proofing at 80 degrees two times and nothing happened. The King Arthur's website recommends 100 degrees, and this is what worked for me!
Thank you for this post, I just found a yummy pizza dough recipe and it told me to "follow the instructions on my bread maker" WHAAAA? what breadmaker? then I found another and it starts with "proof your yeast" but no link, no explanation.... had a link for the word "food processor" which seems to me most folks have heard of. anyhow, that's my rant. THANK YOU :)
Honey works just as well as sugar!