Burr Grinders - a "basic" primer.

When I'm asked to recommend grinders, I have a "trifecta" of offerings I bring up: the Capresso Infinity, the Bodum Bistro Burr, and the Baratza Encore.  We sell the last mentioned, the Encore.  They all come in at relative price parity $150-200 CAN, and all offer relatively similar performance. 

However, there are a number of much cheaper burr grinders that exist in between cheap-o whirlyblade grinders and the ~150$ trifecta offerings.  These mid-range or super-budget burr grinders largely go unmentioned and ignored in coffee communities, and maybe why is never quite explained clearly enough.  

Here goes my attempt. 

The biggest factor in a grinder's "performance point" is overall particle consistency. Connected to that are the nature of the motor or drive, and lastly to a fairly small degree, heat retention.

Particle size, though, particle size is king.

As background, sorry if this is stuff you know: The amount of time it takes to ideally extract any given morsel of coffee is a factor of the ratio between it's surface area and its volume. As the exposed surface rises and contained volume falls, the particle will extract progressively faster - the water doesn't have to travel as far or penetrate as much bean-structure to "unlock" the tasty bit. However, there's a downside - each particle also contains some flavour parts that are undesirable, and once the water has taken all the good stuff, it just keep taking more even when only the bad stuff remains.

If your grinder is putting our particles all approximately the same size, your entire brew mass will take the same amount of time to extract ideally - each particle will unlock and extract at approximately the same rate, because the surface area : volume ratio will be similar. However, there's no grinder in existence that actually produces entirely one size chunk. And variance in grinders isn't as modal as might be desirable either, generally it's a bimodal curve with the "target" particle size being the larger, and a second peak at a substantially finer size (imaginatively dubbed "fines" in coffee parlance). How much of your brew mass is fines has a exponentially increasing effect on your brews, especially across drip or pour-over preps; the fines extract much faster than your target particle does and will inevitably have fully overextracted by the time your target particles extract properly. The more of your total brew mass that is fines rather that target of course, the more represented that overextraction will be in your cup - I'm sure you can imagine how if 5% of your brew mass if fines, it would be much less noticeable than if 50% of your brew mass is fines. Smaller amounts are inevitable and have relatively negligible effect on the cup, while larger amounts have a sort of compounding effect.

Because fines will generally settle and be carried to the bottom of your brew (they won't retain air well enough to float, unlike most everything else in your cone), in sufficient numbers they can begin to slow your brew by clogging up both filter and brew mass, meaning that water has time in contact with both fines and target particles to extract - so not only will your fines definitely overextract, but your target particles may also begin to as well, because of how slowly the water is moving through your mass. (This is not the case with immersion brewing, but then again, for most of those options you end up getting fines in your teeth rather than your filter so harm is both more apparent and a more matter of preference.)

In simplest form, the most a grinder costs the more consistent it's particle size will be, and this stays fairly consistent until you start approaching $1000 models, at which point specialization, branding, and competition start factoring into cost in more impactful ways than the relatively marginal performance gains available.

The even-more complex details of particle size come down to burr configuration and motor. In both cases, our end desire is that beans are essentially repeatedly cut into increasingly small size pieces until they reach our target size. Because the beans are organic material and uneven in texture and just won't be nicely cut into even little pieces, even in this method some fines are still produced. Two other things can also happen in a burr grinder that produce far more fines: crumbling and shattering. If the burrs are dull, moving too slow, or not beveled right, beans will be crushed in between the burrs, but they will be crumbling into uneven pieces until the maximum particle size your minimum, and will produce a spectrum of fines below that point, as well as a few chunks that might be bigger but slipped through sideways. If your burrs are moving too fast, beans will be hit hard enough to shatter, rather than held in place and cut as burrs act against one another, this again creates many too-small particles as the bean shatters, and any pieces too large will be again shattered until they are all small enough to pass through.

So as far as the burrs themselves, many cheaper burrs will use more robust cutting faces to provide expected durability across a cheaper base material. Others will use a very "aggressive" bevel to provide longer-lasting perceived sharpness, similarly to save on a more expensive burr material. As far as motors, as best as I can tell (not an expert on electric motors as a topic) a motor suited to provide cutting is expensive or difficult to manufacturer. Either way, cheaper burrs seem to fall into one of two general failings - best generalized as too fast or too slow. These often match the above two "inferior" burr types, in order. One type is designed as slow moving, high-power drive with "crush" burrs to aim for a believably consistent pulverization. In others, they'll use an overly high drive with a moderately "aggressive" burr so that rotational momentum prevents jamming, allowing an overall cheaper motor, but with the side effect that the grinder is essentially relying on being able to shatter any beans it cannot cut. The first will generally produce more dust, but feel more robust and durable; the latter is dubiously "better" of the two but will sound and feel less robust and generally have a burr lifespan much shorter than the whole appliance lasts - or at least would, if they weren't prone to simply burning out after jamming up a few times.

In all cases, upgrading to a burr does produce some gains in terms of particle consistency over blade; the reason I'm particularly vocal about the entry level "Trifecta" being the Encore, the Bistro, and the Infinity ... roughly in that order is twofold: the more subjective "will you notice and enjoy the change?" gains obtained spending the extra 20-30 on a ~$50 burr don't directly match the investment, while spending the ~$160 on something like an Encore or other Trifecta will, for most people, provide a relatively immediately apparent change in the cup of coffee they're brewing. So at the core, I feel it's the most impactful "layer" of gear upgrade; so unless you're heading towards espresso, upgrades beyond a Trifecta grinder also become relatively marginal gains again. In most cases, I figure someone is very likely to want to upgrade to *at least* the performance point a Trifecta grinder offers, but may not necessarily want to upgrade *past* one of those options. 

The super expensive stuff is generally characterized by increasingly marginal performance gains with the actual improvement taking increasing effort and precision to exploit during brewing. For instance, pushing boundaries of extraction values while avoiding the impact of fines on taste get harder and harder as the brew goes on and as extraction increases. Most people brew coffee at an extraction between 16-20% taken from the brew mass, because with most grinders the fines produced begin to have a perceptible impact on brew taste as extraction crosses above 20%. With exceptionally high end grinders, it can for instance be possible to reach 24% extraction before overextracted notes begin to be perceived, but that does of course take a brewing ritual that is able to control and adjust for all the other possible variables (time, water dose, evenness of extraction via technique, etc.) or the high-end results from the grinder are largely pointless; if they're high-siding their brew and only partially extracting the stuff left near the top and way overextracting the stuff near the bottom, even getting numerically perfect extraction and having the capacity to check that is meaningless, because the taste will still be impacted by the two extremes of extraction present in the cup in spite of removing the correct amount of mass from the grinds.

Lastly, heat retention: as the burrs pulverize beans, they grind against the beans and the beans grind against them and all that friction creates heat.  And a bunch of it.  This isn't a big deal if you're grinding a small-ish amount occasionally on a midrange grinder.  But on something cheaper, the burrs and motor are entirely set up to prioritize meeting performance minimums, and no effort is necessarily made to make sure the burr can adequately shed heat over a long grind or a few sequential grinds.  Any heat build up can be transferred back into your dry grounds as they pass through; heating the coffee before it hits water can seriously impact taste.  For this reason, very low end grinders can often provide a relatively satisfying experience in the short run, but fall short if you're ever called on for more than one or two pots back to back.  

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