Stones In Coffee An Ill Advised Investigation

Today we're going to answer a question that's been at the back of my mind now for literally years, one that I'm kind of weirdly excited to answer. What happens if you get a little tiny stone in your bag of coffee beans and that somehow makes its way into the grinder? How bad is that? Now, many of you watching this will think, why would you worry about this? I've never had a stone in my beans and most people never will. Now and again people do, they often post to the internet about it, so it's kind of top of mind for a lot of people even if it's not something they've experienced. I want to test this and I can test this and so let me talk you through what we're going to do today. In a second, I'll walk you through how stones might end up or not end up in your bag of coffee beans and then we'll get into the meat of the testing. I have a grinder here, we're going to grind some stones with it. It's not all stones actually, it's some foreign matter, just to spice things up a little bit. We've measured them all, we'll show them to you and then we'll put them into a dose of coffee beans and we'll grind them. And what we've got is a set of burrs in here that we've already measured. We've photographed them, we know what they look like, we've got a grind control sample from them. So we can see if a stone damages your burrs, can you see a change in the particle size distribution? Now I could be wrong here, but I'm going to say I don't think you're going to see a change. As I look at a set of typical burrs, there's already quite a lot of damage in there where we've cut three holes for circles to put screws in. I think about that, what that's done to the cutting teeth compared to what a small piece of stone might do to it when you grind it. But now to me, somewhere else, to tell you about the whole deal of how stones get in or get out of a bag of coffee. Hi there, we're here inside a roastery and I'll show you this. It's a small de-stoner. It looks quite big but it's actually quite small. This is for smaller batches of coffee and the way that most de-stoners work, in fact all sort of traditional de-stoners work, is that you load the coffee in the front and you've got a great big fan sucking up air and it sucks the coffee up this tube. So far so easy. The secret is you set it just right so that the suction is right that it can pick up coffee beans, which are not very dense, they're quite light, and can't pick up foreign objects like stones or bits of wood or bits of metal. Those stay stuck at the trap, you empty that out and you've got any foreign material that may have been in the coffee. A practical demonstration. So this is used on a 15 kilo capacity roaster and for a bigger roaster you just have a bigger setup but the system is basically the same. But how do stones end up in sacks of raw coffee? Well it's pretty unlikely and it's actually pretty difficult to give you one single solitary answer to that question. Coffee is grown outside, it's processed, it's often dried outside. There are just opportunities when you're sort of working with large volumes of coffee to have the odd bit of patio stone almost or just stone from outside work its way into a batch and sneak all the way through into a finished sack. As I said it's pretty unlikely. The types of stones that you get can kind of be divided into two. There's the ones that look like little bits of patio that look like they're almost made of cement or concrete and then there are sort of just regular pebbles stones that you might see sometimes. Occasionally you do get other stuff but it's pretty rare like the odd bit of metal or the odd bit of wood. These are all picked up by de-stoners. The tricky bit can be that smaller roasters tend not to have de-stoners and they're more reliant on catching them sort of in the cooling tray and having a look there. Most roasters will obviously pay attention to the coffee as it's cooling. Bigger roasters tend to all have de-stoners attached to them as part of the sort of process and that's what's typically removing most of them. Once in a blue moon though I guess one can sneak through which is why we're making this whole video. All right let's set the parameters and why we've chosen what we've chosen. The grinder the DF64 Gen1. It's got a pretty chunky motor in here it runs a reasonable wattage at a high rpm should have a bit of torque should stand a pretty good chance of actually getting through some stones potentially and certainly impacting with enough force on on a sort of hard to break stone that we should see some damage on the burrs potentially. As for the burrs themselves a bit of a controversial choice we bought these just out of curiosity they are the kind of Aliexpress knockoffs of the SSP burrs. I'll say right now on two levels I don't recommend buying them one we're just not really fan of knockoffs here we think that's good I get cheap is good but at the expense of someone else's business seems bad and two they don't do the greatest of jobs to be honest so on those two fronts really don't don't get those but pretty good for us to smash some stones with I think or I hope the first thing we're going to grind is not a stone is this little guy it's a little tiny piece of wood you know start easy start gentle see what happens we'll let the grinder have a hot start throw this in the beans give it a little spray we don't we don't want static imagine if this breaks the grinder immediately wouldn't that be good a bit noisy look at that that's made pretty short work with a bit of wood that's you know not surprising to me that the burrs running at this speed would smash the wood pieces we'll give it a clean out have a quick inspection of the burrs and proceed now it's time to escalate things a little bit I have here a stone kind of a stone these little tiny bits of stone are probably the most common thing I see when people post about finding stones online these are most likely to come from a drying patio potentially uh so they're almost like bits of grout sometimes uh they look kind of sandy in appearance so I think this should just pass through but will it let's find out like a hot knife through butter nothing at all breezy noise on the slow down sounds like something might be stuck on the sweepers shall we have a look I'm not gonna say I'm disappointed but everything seems fine there's no visual damage at this point let's escalate things with a bigger stone reset same touch point same zero try and keep those particle sizes pretty similar now for the same thing but bigger this size again you see quite a lot of the internet you may be wondering what if I drink the stone look I'm pretty confident that it's not soluble so you're probably fine I don't I don't think you taste it in there I don't know how you do that test we could probably do that test at some point maybe we should do that test at the end anyway we should hear this one because I didn't hear a thing last time I feel reasonably confident saying that if you get stone like that or if you hear a stone like that nothing bad's happened because we couldn't see a thing on those burrs I think it's time to escalate it further again this is where I kind of hope the geologist in the comments who can tell me the kind of rock that we're looking at here but this is a stone stone like a stone it's like a little stone but it's a stone this one I expect to hear this one I suspect might jam the grinder so I'll keep my finger ready by the off button now I'm nervous because I got to step back I didn't even hear that one I don't see a stone do we just do we grind a stone like a real stone okay let's escalate it further we're slightly disturbed by how easy it was to break the last stone so I'm just trying to see if through my sheer force of power like I'll break the stone okay so that's a pretty stony stone this one's bigger again I suddenly have a lot more faith that this grinder will smash it up this thing running at 1400 rpm for us is really useful because if it does jam it'll be spinning so hard when it jams that we should really see some good solid burr damage and that's what I want to test I want to see at what point damaged burrs start to produce a different grind profile all right oh wouldn't be the first time why am I disappointed this is such a weird emotion well we've got to see what that is oh wait see he hasn't gone through now we've set this relatively fine but it has proven resistant to grinding by being too large of a piece choices choices we could try again or we could go slightly coarser so we're going coarser up to a kind of filter setting on here we're grinding at 25 on this thing if you know this grinder with zero being the touch point and so 70 bit coarser maybe we can get that stone deeper in the burrs oh look at this yeah the stone the stone ate it look at that stone whoa not gonna lie that was surprisingly exciting let's have a look inside I'm so disappointed if it looks the same oh dusty burrs there's there's like a little bit I think of damage here on this sort of big cutting tooth that isn't going to be a part that does a lot of final cutting in a burr set remember it's the edges here that really determine your kind of finished particle size the bigger teeth towards the outside really a kind of pre-breaking teeth so if they are imperfect I can't imagine that ruins the day we'll we'll find out and again looking in here you can see like a little bit of damage but not very much so we'll escalate things further see if we can cause some real damage our final competitor it's a good little again geologists in the chat come on what is this what is this for grinding want to go back to our core setting again in the hope of sucking this thing in of course we've grabbed a sample at the final setting to see if the damage is visible yet I'd be very surprised if it wasn't very exciting well it's just breezed through that that's like again geologists what kind of a layer is this what kind of a layer in the bed of the earth have we discovered here can we mine this we'll get it in the particle size analyzer we'll see what we got now like any normal person I've got my video microscope here to have a little bit of a closer look not seeing a lot of damage it looks like just a really intense coating of tiny pieces of stone I will try and scrape some off to see what happens damage anywhere we move over to the blades they're all looking I was a bit damaged there I mean that's a clear bit of damage but I can you taste it we can do better than that it's time to escalate one more time now is health and safety time right our last contender is something that's very unlikely to end up in a bag of coffee beans bits of metal they're very heavy so if you have any stoner they don't make it through but let's imagine that it did make it through buddy now I did hear one good solid impact but let's see if uh any visible damage to you oh it might have just been bent out of shape slightly we'll try again and we'll go a little coarser this time in our last desperate effort I have two screws and a washer right great success finally we jammed the grinder we found some violence we found significant damage bear in mind this is still under a microscope and we're looking at you can see the size a kind of cutting tooth here and so it's quite a small bit of damage but it looks good doesn't it well bad I suppose if it was yours it is it's mine the conversations obviously turned to other grinders here behind the scenes a conical grinder will obviously allow more stuff in than a flat burr grinder and so I guess we're gonna have to do this again just quickly as a replication with a conical burr grinder something like a niche that has a decent motor on it we just grind the stone maybe we need to just try a bit harder going bigger this time still not convinced it's gonna jam but it might jam it's 300 rpm so it's not like a fast motor but it's a pretty solid motor in here it's just grinding the stone I see no visible damage of any sort on these teeth none on the cushioning teeth on the finishing teeth anywhere this thing just plowed through stones as you can tell from the change in knitwear it's a different day it's the day of analysis what we did is we took all the copy that we ground and we ran it through our particle size analyzer we have one here it basically photographs every particle we feed it and it gives us all the data about the distribution of particle sizes it's pretty good way of objectively saying has this grinder's ability to grind coffee notably changed all right let me show you the chart so this is control versus stone five along the bottom the x-axis is size from the little tiny pieces at very small micron counts up to larger pieces and then the y-axis is the percentage of total volume that these pieces make up so you'll see here there's a little sort of hump around the fine pieces and then a second much bigger hump around the sort of coarser pieces but basically looking at this chart looking at the two things overlaid i see no change whatsoever to the sort of output of these burrs based on having ground some stones and you can look at a total surface area and compare the two which you can do here again they look very very very similar even though those birds have been grinding up stones and actually you can look at the sort of number of pieces at each size obviously because there's so many tiny pieces this skews way towards the fines and so you lose the ability really to see the bigger pieces confusingly but again here kind of the same so are we saying that stones don't impact the grinder maybe but before we get into what this actually means for you practically if you find some stuff in your coffee let's talk about the one thing we did afterwards that has produced an interesting result which is grind some metal stuff until the burrs got angry and the grinder jammed now we have to leave room for operator error in this what we would do after opening the burr sets is we would zero them out using a kind of touch point we basically screw them into they just touched set that zero and then move back a sort of fixed amount for our grind setting and almost every time this worked really really well it produced an identical particle size afterwards even though it had been grinding stones but once we got some in there when we did the same procedure the grinder began to grind quite differently that same touch point and then back a fixed amount produced a slightly coarser grind setting than it had done before and i'll show you that data here so you see the control so before it all happened you'll see after we put some metal through it which is notably coarser so you'll see a sort of a peak and especially the bigger pieces further to the right on the chart so that that's further to bigger and then we adjusted it back a little bit and and even they're not quite fine enough maybe so it's what sits in between the two so for some reason something's sort of changed is it the burr set is it the damage to the teeth i i'm not sure that could be the case have we somehow done some structural damage to the grinder somehow that's changing something about the way the burrs are getting close i mean this is a fraction of a millimeter we're talking but something has changed but don't forget there is room for operator error which is me again just for comparison we can look through at the surface area of these and see is there difference i don't know if it's grinding differently anything other than by coarseness i i don't think it's changing the way the burrs are grinding but it seems to be someone smart in the comments give me an idea suggest what i have obviously missed that could have happened here that would cause this because it's kind of weird all of this aside let's kind of answer the most important question which is i find something in my bag of coffee what should i do firstly if you find a stone let the roaster know they want to know if they are de-stoning properly they may need to tweak and adjust their de-stoner based on something sneaking through so if you think you've ground a stone though well don't freak out don't you've probably done no damage to the grinder however if you open your grinder up and you see some obvious damage sort of cosmetic damage to the burrs i could understand how you could be frustrated through no fault of your own you've had a cosmetic damage to your property and if somehow buying a bag of beans caused the side of your grinder to get a big scratch along the side that would also be annoying it doesn't change its performance but you would be right to be annoyed now in the past a lot of roasters have freaked out and i think replaced a lot of burr sets and i i don't know if the cost and waste involved ultimately in doing that is a good thing always don't get me wrong the roaster should absolutely make it right but i'm not sure if you've ground a stone you should freak out and demand a new set of burrs because i'm not sure that it's worth it ultimately the cost the investment all those other things just the waste the shipping the money like it just doesn't seem necessary you should absolutely get some free coffee or some other form of compensation if a stone has jammed your grinder then chances are your motor doesn't have enough torque and violence to really damage the burrs ultimately right like at 1400 rpm we smashed a stone into these burrs made no difference whatsoever so stones are weaker than metal the kinds of stones that are going to make it through a destoner that are found in kind of coffee are clearly not as strong as as burrs with the metal of burrs if you found a bit of metal or you ground a bit of metal then you may be entitled to entirely new burrs but i would still test them afterwards and i'd still be surprised if you could taste a difference look clearly it's a different day judging by the units of knitwear here the point is the reason we're back we felt perhaps a bit blasé being like everything's fine if the stone goes in your grinder it's fine because i read a bunch of stuff on the internet where people claimed the stones genuinely destroyed their grinders and i was like oh maybe we just haven't tested the right grinder so just quickly we'll grab a few more grinders of different natures sizes price points and we'll just try again because if i am so confident that nothing bad is going to happen then i should be willing to put some fancy burrs and other grinders and other things to the test to see if i'm indeed up first is the studio's long-suffering commandante we have of course the stone for the test we're going to use this size stones for everything so i'm going to show you them each time but we're going for like a standard bean-sized stone today's grinder stone i'm so strong all right i'm as surprised as you i thought there was going to have to be like some sort of manly wrestling with the grinder clearly not the case up next uh everyone's favorite false burr grinder these will have ceramic burrs inside completely useless at doing a very good job of grinding coffee i would say if there is a single burr set i expect to be damaged by a stone it would be these ones so it took a little while to get the stone to go and had to set the grind pretty course it was just bouncing around it wasn't getting drawn into the burrs and then it went with a kind of puff of smoke yep definitely grab a stone i mean they look dusty i'll give them that are they going to do a materially worse job is that actually possible i don't know i don't really see meaningful damage to them so we're going to add our stone and of course give it a little spray this is an ode one we don't want a staticky mess now this is interesting for two reasons it's got ssp burrs inside it and also it doesn't have the strongest motor this is the most anticlimactic selection of things going on here i feel like if i was watching this i wouldn't believe it i'm just gonna throw a stone in live feel like a little magic trick the stone smoke stone did you get some smoke yeah while i don't particularly worry about stones in grinders at this point because through my sheer intense physical power i hand ground a stone today i just don't think most grinders will have an issue with them i think a bunch of grinders won't accept them unless you're grinding really really quite coarse the fact that a false burr grinder just kind of powered through it that this thing which i've sort of had stall on lighter roasts powered through the stones means that for most of the stones you're likely to find in coffee which are kind of in my head kind of patio stones so to speak not a huge issue the kind of pebblier harder stuff maybe possible but i just don't see that when i when i see people's images online of stones in their coffee i tend to see those kind of patio stone style stones i really need someone to tell me the right words for these kind of stones that would be helpful anyway uh i'm not saying don't worry about it nothing bad can ever happen but i'm saying perhaps we worry about this a bit too much there's only one sensible way to wrap this whole video up i must taste the stone i'm going to grind one more stone and we're going to drink it and see if i can taste it let's find out so i have my bonus stone which is 0.9 grams on top of my 15 grams of coffee let's see what happens there it is you know in those horror movies where they kind of unearth some sort of bacteria is this nothing can be trapped inside stones right let's taste it as always if you want the one cup technique that is linked in the description down below or up here if you're device i have myself a little bit of stoneware shout out net shack uh to do our tasting from seems appropriate unless it was gonna tell me this isn't stoneware and i don't know my ceramics in which case how embarrassing no not even a touch of flintiness no minerality whatsoever it's just like it's not nice coffee so disappointed i'd hoped for a sort of hint of earth yeah basically you can't taste the stone i don't think i was surprised by that i think if i sucked a stone this is getting weird i would struggle to get much flavor out of it and actually grinding it down and putting it with a very flavorsome thing like coffee means that you can't taste the stone which is a shame all right that is an exploration into what happens if you get a stone in your coffee and you grind it anyway and it turns out not very much if you get some metal in there yeah you should freak out that i guess is the summary of this whole video but now i want to hear from you down in those comments below if you've had a stone you're going to tell me about it and that's going to skew perception of how frequent they are but maybe how many times you've had one versus how many bags of coffee you've ever bought that would be the interesting thing if you're like three stones in 60 bags that's a lot if it's one stone in like 200 bags of buying coffee that's maybe less but i'm still kind of curious what the numbers look like let me know let me know your thoughts ideas suggestions feedback all of that good stuff but for now i'll say thank you so much for watching maybe have a great day