Introduction: Gourmet Mushrooms in an Old Coffee Cup

Picture of Gourmet Mushrooms in an Old Coffee Cup

This is a cheap and easy way to produce lots of tasty fresh mushrooms for the kitchen, while at the same time reducing your own waste and even handling some extra.  The idea is that you will use an old coffee cup as a container to grow oyster mushroom mycelium, which will in turn produce fruit in the form of mushroom bodies.

Step 1: Materials

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The best part about this project is that it is dead simple and most of the materials can be acquired easily and for free.  Really all you need is:

Empty coffee cup(s)
Enough coffee grounds to fill your cups
Oyster mushroom spawn

I'll assume you can manage to scare up some empty coffee cups.  Ideally you want the little plastic lid part as well.  It will make things simpler.

Coffee grounds are really easy to procure.  You're gonna need a decent pile of grounds so the best way to get them is just to head to your local coffee shop with a 5 gallon bucket.  Just ask them to throw their grounds into the bucket and tell them you'll pick it up in a day.  Starbucks says on their website that they will always give you grounds if you ask.  I've had great luck hitting the local indie shops.  The people who work in those places tend to be cool with the project.  You don't want to get grounds that have been sitting around because that will only increase the likelihood that mold will start to form.

The mushroom spawn is something that you will probably have to buy.  I would recommend just buying a block of espresso oyster spawn from Fungi Perfecti here:

Step 2: Put It All Together

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Once you have your materials you are ready to go.  It's best to try to use your coffee grounds relatively soon after picking them up.  If you get them from someplace that makes a lot of espresso type drinks then the grounds will have been steamed so they will be fairly free of contaminants.  The longer they sit around the more likely they are to start getting moldy.  I used grounds from a place that made mostly drip coffee and they seem to work fine.  Coffee grounds seem naturally resistant to contaminants. 

You're going to be mixing some spawn with the coffee grounds in your coffee cup.  You want the grounds to be moist but not wet.  The kind of environment you could picture mushrooms liking.  I find it easiest to add the grounds I'm going to be using to a bowl and moisten it all at once.  It makes it easier to tell if things are too wet. 

Fill your coffee cup about 1/3 full of your wet grounds.  Then break off some of your mushroom spawn from the block and crumble it up into the cup.  You want to add around an equal amount of spawn and mix it with the grounds pretty thoroughly (I find a chopstick works well for this).  Then simply fill the cup the rest of the way with moist grounds, pack it down lightly, and replace the plastic sippy top and label the cup with the date.

Step 3: Now Forget All About It

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Once your cups are full they want to sit for a week or two in a dark warm place.  Temperature isn't too important because oysters have a really wide comfort zone.  Really the best thing you can do is to leave them alone for at least a week or two.  Hopefully the grounds are moist enough that you won't need to add any water while the mycelium is growing.  But if you live in a really dry area you may want to give them a spray of water if them seem to dry out.  The only problem here is if the cup itself starts to get soggy and melt you will likely start to get issues with mold.

When your patience runs out and you check on them you will be able to recognize the first signs of mycelium.  It will look like spots of delicate white ropey stuff growing on the grounds (pictures below).  If there's no activity just give it more time.  Oysters are very forgiving but things may take more of less time based on environmental factors.

Unless you are very lucky you will probably end up having some cups develop spots of green mold.  It's a common frustration of mushroom growing.  Mostly you are trying to get your mycelium to out-compete the mold because you will never be able to avoid it completely unless you happen to have a clean room.  If you do get spots of mold you can try to delay it by filling a spray bottle with hydrogen peroxide and give the mold some sprays.  Mycelium is actually very tolerant of peroxide so it makes a good choice for keeping things clean.  Just be careful because based on the concentration peroxide can burn the skin.

Step 4: When Things Go Wrong

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It should be noted that growing mushrooms at home can be a bit tricky.  Even the simplest mushrooms like oysters can be a bit moody and your results can definitely vary based on different environmental factors.  The good news is that while it can feel frustrating at times to get the mycelium thriving it is very hard to kill oyster mushrooms completely.

In my experience the most common issue you will run into trying a project like this is ending up with moldy cups of old coffee grounds instead of tasty mushrooms.  I had this happen quite a few times and got a bit frustrated.  So when a particular cup got too moldy I would dump the grounds and cup into one of my worm bins that was without worms at the time.  I did this with a few cups of grounds and after a month or so I took a peak to check on my worms and was surprised to see lots of mycelium growing. 

I poked around a bit and the mushroom spawn definitely seemed pretty happy so I stirred in a little straw to lighten the medium up a little and a couple weeks after that I checked again and found a crazy explosion of growth.  The bin was in my basement so was never very warm and definitely stayed very damp.  I guess my point here is that mushrooms are very complex organisms and experimenting with growth parameters can definitely have good results. 

Step 5: Fruiting Your Cups

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Once you start seeing mycelium activity on the surface of your cups you are pretty close.  After another week or so it will you will see the mycelium filling up until the whole surface of the grounds is completely white.  You will also see areas start bunching up.  These spots are where the mushrooms will start forming. 

To fruit well at this point your cups need air flow and indirect light.  You don't need much light and you really can't have too much air flow.  It would also be best to keep them someplace fairly moist.  You really don't want the cups to get dry at this point so something to cover them up with to hold in the moisture will help.  If you have a plastic seedling box thing or something like that it would probably work well.

Below you can see pictures of some cups with mushrooms starting to fruit.  I will post additional pictures as they get bigger but you can see how it's going to work.  As a final note I'll say coffee cups seem to work well as containers but I've tried many other materials with mostly good results.  For awhile I was filling everything in my house that wasn't nailed down with mushroom spawn.  Plastic containers, canning jars, old food containers, you name it.  So have fun and experiment to see what works best for you.  You can see some pictures of other containers I've tried below.

Step 6: Harvest

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This is the fun part.  You want to harvest your mushrooms when they're still fairly young and tender.  Also before bugs get to them.  At this point I have oysters fruiting in all kinds of containers.  One big trunk full of coffee grounds produced almost 10 lbs of mushrooms on the first harvest.  After one harvest you can let the substrate rest for a week or so then soak it down with water and it should give another flush of fruit.  This can be repeated up to 5 times for oysters but 3 is probably more typical.

Also you can see a pick below of a plastic bag that started fruiting oysters out of a little hole.  I didn't even innoculate this bag intentionally.  It was just a moldy bag of old coffee grounds sitting in my basement that some spores must have found their way into.  This illustrates two important things about oysters:

1) They are insanely aggressive!  They will eat anything so are really fun beginner mushrooms as all other species are considerably more picky.
2) They drop a TON of spores.  This is kind of cool to see but note that breathing in spores can be very bad for you especially if you are fruiting these indoors.  Some people have developed very bad allergies as a result of living around oyster spores.  If you want to do a bigger grow I would definitely recommend fruiting them outside where fresh air can take the spores away.


Wetfoot (author)2016-12-29

Incredibly good "ible", & a tasty one for those of us that enjoy eating great foods, ... I am also doing some worm farming, on a small scale, & am also curious as to see if these 2 can be combined, or if they must be maintained separately,
... I also have 2 small aquriums, that I am interested in raising crawdad's lol!

hrussell3 (author)2015-10-28

thanks for the idea, but...first, it's; second, that espresso oyster spawn doesn't seem to be available now.

sloamhand (author)2011-09-17

how important is it to have a sterile growing medium? I know coffee grounds are good for that because they're boiled first.

imbignate (author)2010-07-22

Are you saying in this step that you should mix equal amounts of spawn and grounds? The text is slightly unclear.

zzapatista (author)imbignate2011-04-04

If you're really trying to grow mushrooms in this way I would recommend a high spawn rate. Coffee substrate in coffee cups isn't really ideal so doing 1/3 spawn or so would probably be a good idea. Generally when people are growing oysters on straw or something more common they would use a spawn somewhere between 1:4 and 1:10. Right now I have several very large oyster bags made of mostly coffee and I spawned them at 1:10 tops. It depends on many factors.

co2wms7whcc (author)2011-04-04

That would be a buttload of spawn, you should only need a pinch for a cup of coffee grounds.

darrenchittick (author)2011-03-26

Just wanted to add a quick comment about the issue with mold in the coffee. The real problem comes if you're using coffee grounds that are more than a day old. It's amazing the difference between grounds one and two days past their initial use. If you have the grounds and haven't gotten around to using them immediately, you can pasteurize them by putting them on the stove in a pot of water and bringing them to a boil. Pasteurization actually happens at 160 degrees, some recommend holding that temp for 10 minutes. Bring them to a boil and let them sit for a while. Drain them and let them cool. If you pour them into your strainer directly, the pouring of the water should take care of anything on there as well. Some boiling water poured into your cups will clean them up as well. I'm a big proponent of rubber gloves while working with the spawn as well. These steps will help keep the mold out long enough for the mycelium to take hold and out compete the mold.

I buy my spawn from and find that their prices are pretty good and their selection broad. I grow on a straw/coffee ground mix.

Thanks for a great instructable!

hbomb84 (author)2011-02-15

I think if you take the whole coffee ground/mycelium cake out of the cup and crumble it up into something bigger like your worm bin, you will get many many more mushrooms. There is much more surface area this way and they don't have to just grow out of the top of the cup!

paitch (author)2010-07-22

What about growing in a damp root cellar?

zzapatista (author)paitch2010-08-14

Really depends. Is it a damp, moldy root cellar? If so mold will be a problem. And when it comes to fruiting they will need some light and lots of fresh air.

this1kid (author)zzapatista2010-11-01

Was it easy to maintain an airflow? I noticed that you'd had your mycelium in what appeared to be closed containers and plastic bags.

zzapatista (author)this1kid2010-11-01

I haven't had many issues with it. Overall I found the rubbermade bins were probably the easiest containers to use. I left the lid on while things were colonizing and then when they seemed ready to fruit I just took the top off. The bins tend to live on my back porch so they get quite a bit of fresh air.

I tried the plastic bag thing a couple times but it was pretty much more of a pain than anything. It could work though. Once things are colonized you just cut some small holes in the bag and it should fruit out of them.

hardipk5 (author)2010-07-20

Just a question of curiosity if i was to try to grow "Magical Mushroom's" doing this would it work?

zzapatista (author)hardipk52010-07-22

No for many reasons. Not least of which is the fact that it's illegal to order spawn for magic mushrooms like this.

Ivraine (author)zzapatista2010-08-26

It is actually very easy to come by magic mushrooms in nature, especially in fields in the south, so finding the shrooms isn't a problem, but most need either horse or cow dung to grow, so your house will smell like a cesspit... ... And it will be very easy to locate if hippy shrooms start circulating your city, because of its unique aroma...

zzapatista (author)Ivraine2010-08-26

Wow what a bunch of nonsense. I'm just picturing what you're describing here: ---The man finds magic mushrooms in NYC. He throws his nose up into the wind and loudly declares "I smell a cess pit this way!", and off they go across town to find your apartment where you have some horse dung.--- And besides the fact that anyone who thinks horse/cow manure smells like a cess pit has clearly never actually smelled these substances. Monkey poo != horse poo. Honestly it's amazing how you managed to get so many things wrong in so few sentences. Shrooms do grow naturally in the southeast so way to go on that one. I won't bother correcting the rest because as I've said over and over this guide is not about growing magic mushrooms. There are a million out there that are so you should spread your nonsense on one of them.

Ivraine (author)zzapatista2010-08-27

You are very right, your instructable is about growing legal mushrooms and not magic mushrooms. You are also right when you said that animal dung does not actually smell like a cesspit, I was actually raised on a farm, but we still all used it as an expression anyway, I am sorry for the misunderstanding.

Jonny Katana (author)zzapatista2010-07-22

t's actually legal to order the spores in the USA, as they contain neither psilocybin nor psilocin, the active (and illegal) chemicals in hallucinogenic mushrooms. However, let me discourage you from trying to grow them, as... A: The process is much more complex than this Instructable. If you make a mistake, you can end up cultivating any number of extremely poisonous mold species, which can contaminate the mushrooms and possibly kill anyone who ingests them, not to mention fill your home with their spores, contaminating your food and air. B: Hallucinogenic mushrooms are a Schedule 1 substance in the United States. This means that if you get caught, you are no different from a meth cook in the eyes of the law, and you will most likely go to jail for quite a while. In short, it's quite stupid, and not worth it.

joystik (author)hardipk52010-07-23

I do not recommend to grow any illegal stuff. But, for information purposes , growing mushrooms is all pretty much the same. The trick is finding the right kind of substrate for the right kind of muhroom.

Beta_Orionis (author)hardipk52010-07-22

Probably not. They're much more sensitive and require a very clean, controlled, and balanced growing environment.

bustedandbroken (author)2010-08-14

Hello, those mushrooms look great ! How did the mycelium in your worm farm work out ?

Depends on how you look at it I guess. The oyster mycelium took off like crazy and colonized the whole thing. I guess in the process it ate all the worms because they were all gone. I got many pounds of mushrooms off the former worm bins so in that way it was a success. They weren't worm bins anymore though so less of a success in that way. I would overall be careful of throwing oyster mycelium into any worm bin that had worms you wanted to keep.

zzapatista (author)2010-08-02

Actually that's a good point oysters drop very heavy spore loads. So in general it's a good idea to fruit them outside if possible. I've heard of people developing allergic reactions after growing oysters inside for awhile. I'm sure it varies person to person but breathing spores is never a good idea. Oysters won't invade your garden or anything like that though. They are very aggressive but are decomposers so pose no threat to plants. In fact that would probably be beneficial to plants if anything by unlocking nutrients. Only danger I found was when I threw some oysters into my worm bins and the shrooms took over and i guess ate all the worms. Otherwise they won't take over your life or anything.

zzapatista (author)2010-08-02

Well using a process like I describe here there's a decent chance of getting some mold contamination. And you don't want to be breathing mold spores. But I think some comments here exaggerate the dangers. You're not going to unleash a plague or anything. And once you grow out some mushrooms they're not going to be harboring anything unsafe. You should always cook mushrooms for many reasons before eating but again there won't be any danger of nasties in the shrooms. You could start with oysters from the store. The fresher the better definitely but they're a very very aggressive species so you could get away with a lot. You could potentially buy a bunch and break them up into some fresh grounds. Probably higher chance of contamination then starting from fresh spawn but also lower cost so not much to lose. This will only work with oysters though. Shiitake and button mushrooms require much different conditions to grow. Not sure what you mean by "safe long term". Like i say above people like to talk about the dangers of growing mushrooms but they are basically nill. Just don't keep anything moldy around inside your house. Once you see the nasty green mold throw out the grow or at least put it outside. Mold loves stuffy wet environments so fresh outside air can often give your mushroom mycelium the edge to outcompete some mold. It is actually much much easier to grow them outside, Any time you grow mushrooms inside you are fighting their nature and will probably have more problems with mold. Honestly the coffee cup size grow is a neat novelty but I've found it easier to go a little bigger like a medium size rubbermade container. Mix your grounds in that and throw the top on and put it outside somewhere shady and it'll probably love it. Oysters love fresh air and mold hates it so that is another advantage. Plus with bigger substrates there is more moisture and less chance of drying out. Mushrooms are 90% water so a dry substrate will not fruit. I had great luck with the rubbermade containers I would just make sure to keep them moist. Hope that helps. It does take some trial and error so if you get some mold just try again. I had a lot of failures before I got my process down.

gnume (author)2010-07-22

what do you think about growing them in a big old aquarium ?

zzapatista (author)gnume2010-07-22

Probably depends on the material. I use an acrylic aquarium as a fruiting chamber so that i can control temp and humidity. You could just fill it with grounds and fruit directly out of it but the weight would bow out an acrylic tank i bet. Maybe not glass though. Also to remember is that there are a few things that trigger the substrate to tell it where/when to fruit. The biggest is probably fresh air but light also helps tell it where to fruit. If you use a clear container you may get it fruiting along the sides of the container which is kind of a pain. It could possibly work though with some tweaking.

gnume (author)zzapatista2010-07-22

i have a big glass aquarium an 1 m panoramic that is sitting empty and it would be easy to provide it with air only from the top and it easy to warp black cloth around the tank to block light from the sides

gnume (author)gnume2010-07-24

anyone have idea if it will work ? at last theoretically ?

zzapatista (author)gnume2010-07-25

Don't see any reason why it wouldn't work.

flio191 (author)2010-07-22

My question for you is: can you buy some mushrooms from, say, the organic farmers market, and grow off from them, or is the block really necessary to buy from the intranets?

zzapatista (author)flio1912010-07-25

Yep it's doable to go from a fresh mushroom. But it'll definitely be easier to start from some vigorous mycelium that you'll get in a kit.

joystik (author)flio1912010-07-23

Yes, it can be done. Its a technique called cloning. Google is your friend.:)

Mr E Man (author)2010-07-22 OMG So many varieties of mushrooms. Are they all edible? and could they all be grown this way in coffee grounds?

zzapatista (author)Mr E Man2010-07-22

I believe all the kits at FP are edibles. Though they're not gonna like to be grown on 100% coffee ground in most cases. A lot of them will be probably fruit directly from the bag they come in. You will just like poke a hole to get the kit fresh air which will trigger fruiting. They will all come with instructions and should be fairly simple.

aldefork (author)zzapatista2010-07-23

I have grown oyster mushrooms from FP with great success. I found in the winter I needed to use an inverted 50gallon fish tank (two bags of 'shrooms) in a light filled room (indirect sunlight) with a small humidifier. the tank was raised quarter inch to allow air to flow - CO2 is heavier than air so it could escape. I harvested three 'fruitings' of beautiful Oysters. Cost was high but there is nothing like picking and sautee-ing your own mushrooms. Thanks for the inspiration to do it again...

thepelton (author)2010-07-22

Pleurotis are best before the edges of the cap curl upward.

braindead (author)2010-07-18

The oyster mushroom spawn - who supplies this or does it grow naturally in the growing medium? Thanks :)

zzapatista (author)braindead2010-07-19

Nope you can't rely on mother nature colonizing your medium with good things ;) You can buy the oyster spawn from many different sites online (google 'oyster mushroom spawn'). The spawn I used above came from FungiPerfecti. It was the 'Espresso Oyster' kit. It comes as a block of colonized sawdust that you can then break up and mix with coffee grounds. It'll cost you $20 or so bucks.

thepelton (author)zzapatista2010-07-22

Fungi Perfecti was the source of the Pleurotis spawn I grew in sawdust.

thepelton (author)2010-07-17

Some mushroom species are easier to grow than others. I had a lot better time growing Pleurotis Pulmonatis (Oyster mushroom). It requires a good cellulose source for food. It was suggested that it be grown on coffee grounds, but I was able to grow it on hardwood sawdust. It mades a good addition to cooked food dishes, and I think it tastes best with a fish dish.

zzapatista (author)thepelton2010-07-17

Yep most gourmet mushrooms are saprophytic which means they want to grow on decaying matter specifically decaying hardwood. Hardwood alone is fairly simple as a substrate because it doesn't encourage contaminates because there are few accessible nutrients. Of course the mushrooms see it the same way. The traditional substrate for saprophytic (wood loving) mushrooms is 'enriched sawdiust' which means 10 parts hardwood sawdust, 2 parts bran, and 1 part gypsum. Unfortunately the bran is nutrient rich so will guarantee contamination unless you sterilize it and inoculate it in sterile conditions. Oysters are more forgiving than most saprophytic mushrooms.

Beta_Orionis (author)zzapatista2010-07-22

For Pleurotus (especially ostreatus) cotton seed hulls are a great substrate. These are usually available dirt-cheap or free at feed stores, and are pretty inhospitable to anything other than the mycelium. Boiling them and draining them provides the right amount of moisture. Then you can just toss them in a grocery bag until the mycelium produces little mounds, indicating that it's attempting to find a source of oxygen. This is really great for repurposing and reducing waste though and something I've been meaning to try. Great Instructable.

thepelton (author)Beta_Orionis2010-07-22

I read of someone finding a large colony of pleurotis growing on the castoffs from an instant coffee factory. I suppose any untreated cellulose source would work, such as wood chips, sawdust, cottonseed hulls, cocoabean waste, maybe even bagasse (waste) from sugarcane, but I think that spent coffee grounds from your local coffee shop would probably be pretty good, because they would be pre-sterilized by percolation. I grew Pleurotis on sawdust from my garage, and it worked once, but another time I set it up, it was invaded by something green.

sibi12123 (author)2010-07-22

cool i'll use this for my shrooms thanks! :D

Crazy2 (author)2010-07-22

I love mushrooms but to grow mushrooms takes to many steps and chances..

jongscx (author)2010-07-22

Oh, my dad went through a mushroom phase... He also had access to an unused greenhouse where he worked and a PhD in horticulture/plant pathology, so it was interesting. We had more oysters than we knew what to do with >.< delicious and fresh though. We did Shitake and Straw mushrooms too... YUM On a side note, we let one stand just grow the entire season under a cover... we ended up with a HUGE cluster as big as my head and the table was white with spores :-D

zzapatista (author)jongscx2010-07-22

Oysters throw out insane amounts of spores. Sounds like you guys had a pretty cool setup!

luvit (author)2010-07-19

does this attract smurfs? -- this is important. specifically, for smurfette.

FriendOfHumanity (author)2010-07-19

Wow! This is a great Instructable; I will definitely give it a go.

caarntedd (author)2010-07-19

Looks a bit like something I would find in my kitchen on any given day.

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