Please ID whatever is growing on my wooden items
August 12, 2019 9:51 AM   Subscribe

I suspect it may be some kind of salt crystals but is it mold or something else dangerous/of concern? My google skills are failing me. Here are some photos. The stuff rinses off easily in running water or wipes off with a wet paper towel. I'm close to the Pacific Ocean (a block away) and the affected wood is close to a west-facing window that's almost always open. What is it and what do I do now?

The spoon is in a utensil holder on the counter near the open window, and the cabinet is perpendicular to said window. The stuff only grows in the part of the cabinet on the more westerly side. The outside of the cabinets, wood countertops, and other wooden utensils aren't affected - particularly if they have any kind of sealant on them. I also had this stuff appear on some wooden items that were in the most western side of my garage, which has small mesh-covered openings to the west.

The reason I suspect it's some kind of salt is because of how it's white (wood mold seems to be black?) and wipes off easily and is basically contained to these parts of the house that are right near west-facing windows. But I haven't been able to find any similar photos or info in my attempts to research this.

I'm in San Diego, so it's not very humid. I can't think of any other info that might be relevant, but please let me know if you have questions!

I want to know:

1. What is it?
2. Is it harmless, just unsightly - in which case I can just wipe it off as needed? Or is it something I will need to treat in some way?
3. If the latter of #2 above, what kind of specialist or whatever do I need to get in here to deal with this permanently?

Thank you!!
posted by hansbrough to Home & Garden (22 answers total) 1 user marked this as a favorite
Yes that is mold. Se the recent Ask on mold. It is literally everywhere. Most mold is not a concern unless you are eating, huffing it, or especially allergic. salt would be crunchy and would be deposited all over more evenly, not growing in clumps. Mold comes in all colors.

The main way to combat mold is to reduce temperature and humidity, this may not be possible if you keep the window open.
posted by SaltySalticid at 10:23 AM on August 12, 2019 [3 favorites]

It looks like mildew to me. Moisture, lack of air circulation, and organic matter it can sink its figurative teeth into are the three conditions it needs. Mildew is basically harmless but annoying. Wipe it down with bleach to get rid of the current colonies, and make sure all the surfaces are as clean as possible to get rid of any old grease etc. It's probably growing where it is because of the extra moisture in the ocean air, not the extra salt.
posted by drlith at 10:32 AM on August 12, 2019

If it's chalky when you touch it with your fingers, it's salt. Also, for it to be salt deposit, you'd have to have more than just moisture in the air for it to form like that - it would need a much greater volume of water running on and through the wood for salt deposits to form. This stuff looks organic, some kind of mold.
posted by Everydayville at 10:34 AM on August 12, 2019

Could also be grease coming out of the pores of the spoon. Either food grease from something you stirred it with or, like, if you oiled the spoon to waterproof it or something.

What does it feel like? Crunchy, powdery, greasy?
posted by mskyle at 10:49 AM on August 12, 2019

Hi all - thanks for the input so far! I put up a few more photos here for you to see the cabinet stuff more closely. It's sort of furry-looking? Maybe what's on the spoon isn't the same as whatever is in the cabinets - I'm far more concerned about the cabinets. I'll throw that spoon away if needed, but replacing cabinets is a much bigger deal.

Also, for the record: I love science as much as the next MeFite, but I am definitely not going to taste this stuff and am not really too interested in touching it with my bare skin either.

I just found the term efflorescence in my searching and am wondering if it could be that? What do you guys think: (it looks a lot like the photo here on wood toward the bottom of the page) This one says that efflorescence dissolves in water (which my stuff does) but that it doesn't grow on organic material like wood (d'oh).

Mildew sounds like a maybe, but I thought mildew was black??

I can try the bleach and see if that does anything...
posted by hansbrough at 11:06 AM on August 12, 2019 [1 favorite]

I guess my other big question is: do I need a mold abatement specialist?? Or should I be trying to tackle this myself?
posted by hansbrough at 11:09 AM on August 12, 2019

It's probably some subspecies of Penicillium; there are lots of subspecies and it's ubiquitous. If you let it grow, they can range from light green to dark green. Is your area pretty humid?

Generally harmless.

Bleach will take care of it (and don't worry about bleach residue; it degrades pretty quickly).

If you do taste it, it has a particular distinctly bitterish taste.

if you really wanted to, if you sent me a swab of it, I can 18s rRNA sequence it for you and get an identity.
posted by porpoise at 11:22 AM on August 12, 2019 [18 favorites]

porpoise... that sounds so fun (and definitive)!! I sent you a message!
posted by hansbrough at 11:52 AM on August 12, 2019 [1 favorite]

I'm not a knowledgable mold person, but I'd wash all that stuff in the dishwasher, if you have one, with a heated dry cycle, so really clean it and kill as much as that stuff as possible. I might also consider a pre-soak in the sink with a capful of bleach in water. I'd empty out the cabinet and clean it first with soap and then water concentration of bleach the internet recommends. Then I'd leave the door open and let it dry. Maybe even point a fan in there to get air moving.

Air flow is your friend, even with the window open.

But you know what you could also do? Get a good flashlight and look in there and see if you see any sign of water damage or leaking on the wall, under the counter, etc.
posted by bluedaisy at 12:06 PM on August 12, 2019 [6 favorites]

Mold/mildew is furry, salt is crystalline and tastes like salt. You won't generally get salt deposits a block from the ocean. Dishwasher deterg usually has bleach, there's heat, and the dishwasher will destroy wooden spoons fairly promptly. You can make a weak solution of water:bleach with a Tb of bleach in a gallon of water. Make a solution, keep some in a sprayer. It will bleach wood, so use something else on furniture. When I lived near the ocean, and now living near a lake, I can't leave windows open if I'm gone for a couple days, because moisture and still air make mold/ mildew. QFT: Air flow is your friend, even with the window open. I learned this by having to wash that gray stuff off everything, and get a rug sent to be cleaned. If you're gone for more than a day, close the place up. I run a dehumidifier or my house goes musty, and I run ceiling and window fans.
posted by theora55 at 12:23 PM on August 12, 2019

Just give it a good wash.
posted by humboldt32 at 12:41 PM on August 12, 2019 [1 favorite]

I'd be really surprised if that turned out to be anything other than mildew, probably a powder type if it wipes off easily. It could be humidity from the ocean, but it could also be from a leak or something inside, as other people have said. If you want, you can buy a small digital hygrometer online for like $12, and that can give you a sense of how humid it actually is in there. People's bodies are apparently not all that great at sensing humidity levels.

I just had a mildew problem here, and although it was definitely humid outside, the source of the indoor humidity turned out to be excessive buildup of condensation in the AC units. You might notice a similarly unexpected source of humidity if you investigate, and a hygrometer might help with that.
posted by shapes that haunt the dusk at 1:27 PM on August 12, 2019

Um... there is some very toxic mold in the world. Since you're going to get it sequenced, I guess you can find out what it is, but you might have multiple kinds.

If it were me, I'd throw out all wooden food handling implements that had any kind of mold on them, or at least modify them in some way that I didn't every serve food with them. I'd also bleach or sand the heck out of anything moldy in my house - mold isn't something that's good to live with. Yes, the spores are everywhere, but the number we come into contact with, and whether it's growing or not, makes a difference.

If you're living with a lot of humidity, I'd probably stop using wooden utensils.

OTOH, I love me some interesting looking wood that isn't used for food.
posted by amtho at 1:49 PM on August 12, 2019

If it were me, I'd throw out all wooden food handling implements that had any kind of mold on them, or at least modify them in some way that I didn't every serve food with them.

As far as I know, most wood is actually somewhat antimicrobial -- certainly more so than plastic, which can harbor bacteria in the little scrapes and cuts that form over time. I don't think it should be necessary to sand anything unless it's very stained, and even then it's probably fine. If they're powder molds that wipe off easily, I'd think bleach would be plenty to sanitize any wood they came into contact with.
posted by shapes that haunt the dusk at 2:01 PM on August 12, 2019 [2 favorites]

Yeah, it's mold, and bleach - or white vinegar - will kill it but it will keep coming back until you eliminate the source of the humidity. Sometimes, it will keep coming back on wood. Consider putting a tiny fan or tiny dehumidifier in that cabinet. I have managed to demold wooden salad bowls but it took repeated cleanings and oilings - scrub with hot water and bleach or vinegar, then dry, then rub with olive oil, then repeat. Also, it will probably leave a stain.
posted by mygothlaundry at 2:46 PM on August 12, 2019 [1 favorite]

When I lived in a cottage a block from the beach in San Diego, the problems were mold and mildew, not salt deposits. The landlady recommended wiping surfaces with a bleach solution, and seeding activated charcoal dehumidifier containers around the house (especially in closed areas like cupboards and closets). (Check for mold behind your furniture, too.)
posted by Iris Gambol at 3:58 PM on August 12, 2019 [1 favorite]

Surface stuff like this does not justify a crazy specialist. Unless you suspect it is in other places and is growing and you can't change whatever factor is causing the moisture/humidity in the air then just deal with it via surface cleaning methods.

This is not salt.
posted by RolandOfEld at 5:40 PM on August 12, 2019 (it looks a lot like the photo here on wood toward the bottom of the page)

For what it's worth, the URL for the photo of wood at the bottom of the page is [...]/white-mold.jpg. It's mold. That photo is near the section describing how to differentiate mold from efflorescence, and it really should be captioned.
posted by whatnotever at 6:10 PM on August 12, 2019 [1 favorite]

In case anyone is interested (and it appears to be so), these are my memails to hansbrough (address omitted, ofc, etc.):

A few things; I assume you're in the US? I'm in Canada and it's generally not a great idea to mail microbes around. This is innocuous enough, though. Our molecular lab is certified for Plant Pest Containment level 2 anyway.

I'm off the bench these days, but we're doing an environmental microbial survey at our new tissue culture facility ahead of operations, so I might be able to sneak a sample in/ convince the lab to actually type a few colonies and throw yours into the queue. No promises. They totally walked back recently on identifying the bugs that we're going to pick up (or doing something clever instead like throwing the whole lot into a NGS (next generation sequencing) system to get a snapshot/ total-count instead of sequencing individual colonies), so might take some convincing.

Normally, I'd send you a microbial sampling kit consisting of a sterilized swab and a small vial of general nutrient media. You'd swab the sample, swish it around in the media, then send the inoculated media back to me on blue ice overnight.

Normally, we'd streak it out to make sure that it's a homogenous population, then pick a colony(s) to extract DNA and PCR amplify a portion of the 18s rRNA region and BLAST that against the extant database.

This looks like it's probably a homogenous population. If it isn't then th PCR amplification will consist of multiple different sequences and we'd get noise/ garbage from the sequencing (hence streaking it out and picking discrete colonies).

For a quick and dirty, you can take a clean Q-tip (if you have an instapot, sterilizing it in that can help) and swab a larger colony (circular splotch, ideally not one that overlaps another splotch) and try to pick up as much of it as you can. Fold a piece of aluminum foil over the end that you swabbed with like an envelope, securely. I could do a mockup and take a picture for you. Place in a ziplock bag, seal, and mail (slow mail's fine since we won't be shipping in media; shipping in media helps ensure that very small samples remain viable for streaking).

If I can sneak a sample in, we'd unwrap your swab in a BSC (biological safety cabinet) and swish the sampling end in lysis solution, (then bleach everything for 10 minutes), then perform a DNA extraction, take a little bit of the eluate and PCR amplify with 18s rRNA primers, then throw that on a sequencer with one of the primers.

Almost certainly it'll be some sort of boring Penicillium. Alternatively, depending on your jurisdiction, there might be government labs that do this kind of thing as a service; here in British Columbia, we have a provincial lab that will identify anything you send in for a fee (based on turnaround time, not the tests performed - this can be super money-losing, but it's a government lab).

If you want to play around at home, you can swab a colony, then rub it on some fresh bread. Place on aluminum foil and drop a jar over it. Maybe wet a small napkin, wring it out, and fold it into a ball and place under the jar with your inoculated bread - not touching. It should grow at room temperature over three or four days into a greenish-grey splotch with perhaps a lighter-grey halo around the main splotch. If it does this, you almost certainly isolated a Penicillium. If you get a different morphology, then maybe it was something else.

If you want to get fancy, get another clean Q-tip and rub that on another piece of bread as your negative control, nothing should grow on it and if it doesn't then you know you cultured what you sampled and not something that was already on the Q-tip. This is pretty loosey-goosey though.

Toss everything into 1:10 bleach:water and let sit for at least ten minutes, then wash/ toss. Wash your hands with soap and water.

If you want to clean up the extant contamination, I'd make a 1:10 bleach solution (wear gloves), and sponge off all affected surfaces. Let it remain damp for 10 minutes, then wipe with a water-wetted paper towel and then dry. The bleach may... bleach the surfaces that you treat, though. Use fresh bleach (it can degrade in the jug that it comes in over time); if your bleach doesn't hit you in the face, make a 1:2 bleach:water solution instead.

Alternatively, sponge all the surfaces down with 70% isopropanol (rubbing alcohol) and let it remain damp for 10 minutes, then wipe with a water-wetted paper towel, then dry if necessary.

I have meeting tomorrow morning (on another subject(s)) with someone who can greenlight the sequencing.

There are (afaict) actual validated protocols for using an InstaPot and achieving sterilization (with data). You could boil it, but the issue is getting it dry/ cool without it being contaminated again.

"Field sterilization" (ie., sterilization of tools within/ on a certain cap on tech) is actually a very interesting and very nuanced field of study, often an afterthough rather than a field of its own right.

The InstaPot is able to achieve very high temperatures required for sterilization because it's also a pressure vessel. 100'C (boiling - which can be lower at higher altitudes) isn't sufficient.

But because we aren't doing any amplification (promoting microbial growth), any contaminating microbes are presumably far outnumbered by the number of cells/ nuclei that you can pick up (and we can extract from).

The foil and ziploc bag - we generally assume that they are "clean enough" - the issue with Q-tips is that they are typically stored "open to air" (and exposed to MBP, microbe bearing particles, which are ubiquitous) and also organic/ lots of surface area (each cotton fiber has a huuuge surface area compared to their volume) and often repeatedly exposed to higher temperatures/ humidity. Foil is stored rolled up, ziplocs are stored volume-free. Another assumption is that the manufacturing process is inherently inimical to microbes; the assumption is "good enough" for this type of work, but should be verified for anything more stringent.

It doesn't matter that we have cotton DNA mixed in - our PCR primers are specific to fungal 18s rDNA sequences. We can extract DNA from a chicken wing bone and identify the human who ate the meat from it off the residual mouth cells left behind.

If you can get a brand new "travel sized" (or individually packed) packet of Q-tips, that might help; make sure you don't touch the end that you take the sample with.

The foil cover; something like this should be adequate: This is to prevent any biological material that you picked up from migrating too far from the tip. This also helps maximize the amount of biological material that we can transfer into lysis buffer. This also prevents the electrostatic transfer of sample onto the plastic container. All of these protects our facilities, our equipment, and our people who are handling the sample.

Some Penicillium spp can produce penicillin and/ or analogues (molecularly structurally close enough such that they can serve as allergens to your antibodies) - so yeah, it's potentially harmful to you. Deep bleaching should render your wooden kitchen tools safe - even dead wood has "lignin" in it which is inherently antimicrobial - but evidently that wasn't sufficient. Stuff wafting off of the growths on your furniture - probably/ likely too low to trigger a reaction.

Fungal colonies tend to be hydrophobic, so wetting your Q-tip/ swab in (presumably sterile) freshly opened bottled water (in ghetto times, I've used Dasani as PCR water - it's clean enough, low salts/ dissolved solids enough that it can substitute for milli-Q water (assumed to be ASTM class I type A or B) but it's not as reliable and if you're needing to use Dasani water, you don't have the necessary resources to really QC it - make up for it with rigorous negative/ otherwise controls in experimental design).

General nutritive media (I typically use YPD or peptone water) has lipids and amino acids and salts enough in it that it can help "free" fungal bits and aid it to adhere to a sterile cotton swab. If you have a a big enough single colony, the dry Q-tip should pick up enough material that we can get enough DNA to do a successful PCR with. Try to pick up all of the surface material from a colony, but avoid picking anything up from a neighbouring splotch.

Again, if there are more than one species in your samples, that will make the sequencing fail, so try to get just one round (uniform, isolated, typical) splotch - typically, one or only a few spores from the same parent colonizes someplace and grows outward from that initial cell/ small group of cells into a mostly-round splotch.

If we're being audacious - mail the sample (maybe take a couple/ three separate samples/ baggies? - but if sealed, they can all go into the same envelope) to:


I want to stress that this is super NOT rigorous; this is purely a novelty-purpose/ favour for an internet friend thing. No results guaranteed, and any results are not necessarily guaranteed. This is definitely not a medical/ healthcare diagnosis.

We could make it so - but it'd cost real money and time to do so.

We were planning on doing the environmental microbial survey tomorrow, but will likely be postponed until next Tuesday; so if GMLSD can receive the sample by next Thursday (earlier is better) - if I can convince them to type a bunch of colonies - then we might be able to sneak your sample(s) into the process. This would just be taking DNA from your swab, not streak and culture/ subculture (so we won't know if there are multiple bugs in your sample unless the sequencing looks a particular way - in which case, we can only say that there are multiple species, but not which ones, usually).

posted by porpoise at 9:42 PM on August 12, 2019 [3 favorites]

Forgot to add, generallt: if taking a fungal spore/ mycelial sample, do not use cheap synthetic material swabs.

The plastic fiber swabbing ends actively reject fungal spores/ mycelia, especially if electrostatically charged.

"Q-tip" seem to keep using an almost 100% cotton for their ends.

They're decent for picking stuff up, but there are purpose designed synthetics for releasing what you sampled (into another media, supplemented with surfectants), at pickup rates as good as natural fibre. But you won't find those on off-brand Q-tips/ cotton swabs.
posted by porpoise at 10:07 PM on August 12, 2019

Definitely looks like mold. If the window causes a daily temperature cycle due to sunlight etc., it could be that it's just humid enough that when it cools down at night you get condensation on those wood surfaces, even if it doesn't feel that humid during the day. In addition to bleaching or vinegaring the wood surfaces, you could try to address the humidity with an open box of baking soda or something similar. Just place it in the cabinet, and it will tend to absorb moisture from the air, keeping the humidity inside the cabinet low enough that the temperature can't drop below the dew point.

When I took microbiology lab back in the day, we sometimes collected samples using a simple wire hook sterilized in an open flame; would using that instead of harder-to-sterilize Q-Tips work?
posted by biogeo at 11:57 PM on August 12, 2019

Hi all, just wanted to follow up and let you know that porpoise and I were foiled by our respective countries' postal services - I received the package of samples back a couple of days ago. Not sure what happened there, but in the meantime, I wiped the cabinet down with bleach, dried it out for a few days with a fan, and put in a box of baking soda. So far, so good!

Thanks for everyone's suggestions!
posted by hansbrough at 3:00 PM on September 22, 2019 [1 favorite]

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