I know you don't want to paint them but we painted our dusty, rough looking beams white like the ceiling and they all but disappeared. As for cleaning your beams, a brush, with furniture polish or maybe someone has some ideas. Good luck.

I don't know anything about this, but I'd ask Home Depot if you can sand these where they are. Bring your pic.

Sanding is not an option because there are so many of them throughout the house. Plus, they are very rough. I don't want to change them at all - just want to clean and shine them up a little. I was thinking perhaps some kind of oil, but I hoped to hear some experiences before risking an unknown. I can't find a place where a mistake would not be obvious.

You can give the beams a top coat of poly. That'll add luster/sheen/life without changing the color.

Please re-consider your wish to not paint them. I would find their size their size and darkness to be oppressive in a kitchen. If it were me, I'd seal them with a coat or two of a sealing primer, like Kilz, and then give them two coats of eggshell finish paint to match the ceiling. They are rough enough that you can't practically sand them down without a huge amount of dusty power sanding, probably using a belt sander. And even if you did all that work I can't guarantee that it would look ok because you would likely have dips and undulations; I'd just accept the uniform rouigh surface as it is. The only alternative if you want a smooth look is to clad them first in MDF, but that would be expensive and make them even bulkier.

I like the idea of the poly, but, not the glossy type. Get a very low gloss.

My mom had (very) rough cedar on the bottom half of walls in a basement family room. It was a style that was a thing in the 1970's. It wasn't stained dark, natural finish. We painted, primed first, with a eggshell satin finish very light grey. It looks fantastic. Paint is the best choice. The only other thing would be to cover them in smooth wood, stain or paint or drywall, which would cost much more than just painting them.

Do the beams serve a purpose or are they just cosmetic? Can they be removed?

Yes, the beams do serve a purpose - they are the actual post and beams of the house. It is a mid-century modern home, which is why we bought it. We love the style and want to restore it, not hide it. The beams are meant to be a rustic, natural element. Painted, they make no sense. I have considered poly, but I wonder if perhaps an oil would be better for the wood.

I'd try something like Danish Oil before poly. Much easier to apply and refinish, and you don't really need the durability of polyurethane.

Oil attracts dust so if the dusty look is what you dislike oilIMO makes no sense . I have to agree that really dark color is not the natural wood that they are and I would either paint them or clad them in new wood in a more natural color .

How many of them? I like @Patricia Colwell Consulting idea of cladding them in new wood if possible. You might also try to sand them? So they aren't rough if that's what you don't like and it might take off the dark stain? But I'd try it on the most inconspicuous one in case it fails. I'd be tempted to live with them as is.

A friend of mine lives in (now selling) a loft with exposed rough beams. I was up on a 14 foot ladder dusting pipes. The beams were coated with dust that would not come off using a duster. It seems to me that adding oil would just make it worse, but I just found this, for what it is worth:
Treatment of wood beams

They are suggesting beeswax polish. You could get a bottle of Howard's Feed N Wax at Home Depot and test it somewhere in the house.
Feed N Wax

You mentioned posts. Do you have any photos showing the posts' condition at finger height? Ideally, any additional treatment would protect the posts from showing wear and tear. Then you could use the same treatment on the beams for consistent sheen and color. You may have to use a low gloss polyurethane after vacuuming the dust off. Construction dust will add to the dusty appearance- you will have to make sure the crews vacuum it all when they finish. Masking off the beams before they start demolition would probably be a good idea. An oil treatment could turn sticky. Polyurethane is probably a better bet.

"An oil treatment could turn sticky."

As well as make it impossible to finish the wood with anything else down the road.

While I would love to somehow get the brown stain (or whatever it is) off the wood and have them be a natural color, it isn't possible. They are too rough to sand, and even if they weren't, there are way too many of them throughout the house to do anything like that, including covering them. Paint, oil, wax, might be possible, but nothing more intensive. There are beams and posts in every room and on every floor of the house, many of them in nearly inaccessible places. Aside from the expense, we once did try to find a company of person to change the finish, and no one would even consider it. The painters wouldn't even paint them back when we were considering that. I think I can live with the color if they only didn't look so dry and dusty. I guess I will experiment with some oils and waxes in the least obvious spot I can find and see what happens.

They aren't too rough to sand. Sanding is what you do to rough wood. It may take a long time, but to get the look you want, you will have to sand them and stain the color you want. It will be worth the work, though! If that is truly out of your list of options, you can dust with a very rough brush and water. As mentioned more than once, oil and waxes will be a bad choice.

No seriously, we cannot sand them. It would be physically impossible to sand that much wood in the places it is located. If it was just one or two beams, I might try it, but even a contractor won't take that task on.

I also have to point out that these are the actual support structures for the house, so sanding off an inch of wood is probably not a good idea. Sandblasting I think, although I've never done it, I've heard can be done once or twice, but again, too many beams for that and no one willing to do the work anyway.

I hope this blog helps you. They refinished the beams with no sanding and using a gel stain.

https://www.remodelaholic.com/stain-wood-beams-without-sanding/

I am going to try the stain idea in a little spot, too. I can't actually tell what is on the beams now - if it's paint or stain or something else.

If it were me, I would enclose them with plywood and make faux beams. Nobody would know. You could stain them nice too.

@kudzu9, I wasn't suggesting to make it smooth. Here is a great example. :-) https://www.grandmashousediy.com/refinishing-beams/

Maybe if we only had a few and they weren't the actual house support beams we could sand them, although I'm pretty sure a palm sander wouldn't get very far - but I have 20-25 beams and posts ranging in size from 5 to more than 20 feet long.

You could also try painting to look like a lighter shade of wood. If you search online how to paint to look like wood, that may give you some ideas.

Maybe this:

How to finish rough-cut lumber

Unfortunately, the issue is how to re-finish rough-cut lumber....

I would not attempt to sand those. At a previous house, our trim contractor installed an unplaned, unsanded beam for our mantle. I thought it could be finished (sanded and smoothed) later and boy was I wrong. I ended up just leaving it as it was (rough cut and unstained) because it looked okay anything else would've ruined it.

OP, have you considered having existing beams clad in smoother material? That way, you can get the finish you want with a lot less effort.

Way too many beams in too many odd configurations for any kind of covering! Also, I don't mind the rough cut - just the sort of dustiness and dryness of them.

So I found a tiny spot in a corner to try out some Tung oil and some gel stain. They both work as far as making the wood look a bit more....moisturized.

If you want to keep the color they are, and just refresh, you might buy clear tung oil.

Tung oil on right, dark gel stain on left. Horrible carpet soon to be gone in background.

personally i am not sure if it's worth it. I'd focus on rest of remodel and circle back and see how you feel. i have rough hewn beams in my house and don't touch them. so i'm biased.

To me those beams already look like they were painted once upon a time. I would simply prime and repaint. One room or beam at a time :)

Looking closely, it does seem to be paint vs stain. I think. However, it was clearly not painted with a brush because the grain is completely visible. Painting over it with a brush would give it a different, obviously painted look. Also, what color would I paint it? It's supposed to be a rustic beam and have that woodsy 70s vibe, which we are trying to keep, not hide.

To me, the current finish looks like a semi-transparent stain like they use to refinish decking.

^^^ That's what it looks like to me too. If that's the case, no stain or "oil" will penetrate the coating.

You could paint them a similar color, but with something that isn't dead flat.

Perhaps that's it - or whatever version of it they had back in the 60s and 70s. From where it has chipped off, I can see that it is very thin, but much more opaque than a stain (the color under it is a lovely light brown wood). However, there are no lumps and bumps or texture like you would expect from paint.

Even if you successfully oil or stain them a different color they will look dull and woody again in fairly short order unfortunately.

Marie, one of my favorite colors is Behr Berry Brown. We used it on rough exterior beams that were originally stained bright red cedar. We just used a roller to paint these after gray primer. Of course always check color in your own home, depending on the look you are going for. We used Behr Ultra Exterior Satin here.

Are you sure the current finish was applied in the 60s or 70s? Could the previous owners have used something in the 80s or 90s to try to "spruce" up the beams a bit?

Edited to add: I agree with the other poster that I'd wait and circle back to these. From what little we can see of them, I don't think they look abhorrent right now. You could very possibly make them work in your space as they are.

I'm sure only because the other houses in our neighborhood by the same architect have the exact same beams, although many people have painted over theirs (white, which is how I know it doesn't look right).

I'd scrape off a bit the size of a dime somewhere to see what the original (now aged) color of the wood was. If you are in an area where redwood was popular for beams, it'd be nice to find that's what you have. Then you could consider some reddish "redwood" tones in case you decide on a semi-opaque stain.

Your closeup photo also looks to me like they already had a coat of gel stain or something similar on them.

I had the same cedar beams. I beefed them up with rough cut pine which I whitewashed first then basically wrapped the beams. They look spectacular and people always comment on them.

That's so clever! Are those one long beam or did you put together several pieces of wood?

They are 16’long. So several pieces.

As long as the surface of the beams is rough it will always be a problem with dust and dirt...sandblasting or sanding or just using a scrub brush and cleaner are options that are mostly labor intensive...wrapping as an option looks less authentic as a beam...makes the beam bigger .....and always looks like a fake beam....with the added expense of all the material needed....almost all options come with a risk that the walls will be damaged and need touching up ...if it was me...i would try cleaning them first....to maintain the authenticity...and then touch up if any of the color has come off..