How close are store bought broths and stocks to the real thing?

There's a great deal of variation in the quality of the pre-made stocks you get from different sources, so there's no clear-cut answer. Here's the types you might find:

• Stock cubes: these are dehydrated stock, or sometimes just chemicals meant to taste like it. It's the lowest quality option. There's a lot of variation here, I've found some brands (knorr for example) to be better than many others, but still not close to the real thing. I rarely use these
• Stock powders: similar to cubes these are loose rather than cubed powder stocks. The advantage of them over cubes is they dissolve much faster
• Gels: these are more recent, they are super-concentrated stocks in a gel format. They come in little mini tubs, you peel the lid off and squeeze/spoon the contents out. I'm not sure these have made it over the pond to the US yet. They are IMO much better than cubes or powders and closer to the real thing, and I use them more often than any other alternative
• Canned/bagged stock: Most of the time these are concentrated, there's a lot of variation in quality between brands. They have a long shelf life, and don't require refrigeration
• Fresh stock: you can sometimes find fresh stocks in the refrigerator section of the supermarket, or at a butcher/specialist food store. These are the best alternative but can be expensive

Personally I rarely make stock, and when I do I use it right away. When I need to strengthen the flavor of a broth, or I need stock I use knorr stockpots (one of the concentrated gel products), or if I only need a little flavor, I spoon of powder. There are a few cubes rattling around my cupboards for emergencies too.

All excellent information, but can I answer bluntly: none of them come even CLOSE to the real thing. Once you use fresh stock, you will never, ever go back. Really. Making stock is easy, cheap, and as said above, unattended time. Stock forms the base of the kitchen, once you have it, you will notice the taste of everything you make improve so much. Get some bones (most butchers will give the away for free, just become friends) cold water, bring to boil, throw away the dirty water, start again with fresh water. This saves you the trouble to skim the grey foam, which is the white blood cells and other bitter tasting substances. It is also much more effective as skimming. And it results in a clearer, better tasting stock. When you do it, you will see what I mean straight away. I even rinse the pan Add onions and celery, and basically all the cut-offs of all your vegetables. pepper corns, bay leaves, unpeeled garlic cloves, whatever you like. You dont need to peel the onion. The fuller the pan, the better the stock.

On your storage problem: two solutions. Big restaurants do not store, they just have a big pan boiling night and day. Small scale: after a hours or a night of slow boiling or so, remove bones and veggies. Cool. When fat is solid, remove and use this for frying: fried taters, etc.

Now boil down the broth, really down to say 20 percent. You have a demi glace now. Put it in ice cube trays, and freeze. When frozen, remove, and put in bags. You have now concentrated fresh stock that takes up no space, and you can use in any quantity you require.

Please try it. Again: NOTHING comes close to the real deal.

Quality varies. I have yet to find a store bought equivalent to homemade, but there are adequate products. It would be worth it to purchase a few samples and find one you like. I would look for something with little to no salt, as it is better to control for that yourself, in your final product. Having said that, making stock yourself, particularly using a pressure cooker is easy, and can take as little as 30 minutes. Strain and freeze. Without a pressure cooker, the process takes longer, but it is mostly unattended time.

The problem is: Bought stocks tend to have a long ingredients list, and create a "shadow recipe" effect easily - important or problematic ingredients get carried into the dish via some bought product that they were arbitrarily mixed into, confusing recipe writers, learners, recipe followers alike.

For example, a lot of vegetable stocks carry turmeric and arbitrary, sometimes counterintuitive herbs and spices, which you would either want or not want in a dish.

Talking of dried vegetable stocks, they create a paradox: The type that is fortified with some umami source (yeast extract, HVP, MSG...) matches that description of a mixture of things that do not need mixing unless it is meant as a condiment or ready to eat product, the type without (unless it uses eg plenty of mushrooms as a umami source that you would include in a homemade vegetable stock) in the end is more of an aromatic/spice salt than a functional stock.

One thing that is occasionally worth doing, if using such stocks, is boiling a big kettle of water and making and tasting a cup of each brand you have, and taking notes about the differences.

(Recently developing a strong opinion on things recently that are mixed from what needs not mixing, especially if not by a well recognized recipe, and are meant as an ingredient...)

Nothing compares to well made home cooked stock. Almost all commercial stock flavors, cubes, boxed stock, better than pastes, College, Kitchen, Rachael, etc., come from one manufacturing plant. The basic difference is the salt content.