Tipping is a visual marker in coffee roasting that tells us we have applied too much heat transfer into the coffee seed too quickly. As a result of the excessive heat, the coffee seed burns through the tail end where it would naturally germinate. See below for an example of (minor) tipping.
As coffee roasters, we avoid tipping because it is considered a roast defect. Tipping can introduce an ash-y, burnt or smoky taste to your brew, and even subtle astringency to the finish. However, delicious coffee can still have minor tipping. A visual queue is not enough to write off a roast profile. Always taste your roast.
With the same starting conditions in your roast, tipping is more likely to occur in larger and/or less dense seeds. In addition, naturals and honeys are more likely to experience tipping than washed coffees with the same starting roast parameters. Tipping can be resultant of your roast environment settings being "out of tune" with what the coffee seed desires to roast well. Settings that can cause tipping include: too hot of a charge temperature, too much hot air (at any point in the roast), and not enough airflow through the drum. There are plenty of great articles already on this subject so we're not going to spend too much more time talking about.
One good test of tipping on a coffee seed is to try drawing with it. If you can use it like a charcoal pencil, you've found tipping in the wild! Here is that "pencil test" for tipping.
Pre-tipping is the minor markings, decent tipping is the far-right. Intense tipping is not pictured but would be a black, or charcoal, shade. And now, here's some coffee I found in the wild with tipping. (Ignore the middle seed; that is pest damage likely from a coffee berry borer.)
You'd be surprised how many great roasters still run into this problem quite regularly. This was an El Salvador coffee from a big name California roaster. Certain coffee traits, varietals, regions, and processing is much more susceptible to it and can really catch you off-guard. I won't try to generalize all of them.
Another fun fact is that quakers tip easier than normal seeds. You may see tipping in the wild simply from a quaker that made it through sorting.
Using tipping as a tool
Now, how can we turn a defect into a tool. Tipping is something roasters tend to avoid, but in small batch roasting, we have the luxury of low cost per batch during profiling. So, when roasting hot and fast, I actually suggest find your coffee's tipping point! This is a resource to you because it will set an upper limit on your coffee profiling from then on. Here's an example of what I mean.
We charged at 395°F (red), 385°F (blue) and 375°F (yellow) on a wet Natural Ombligon. We roasted in this order too. Our first two batches (red and blue), we try to keep the drum hot when we start. The second attempt (blue), I lower charge by 10°F but try to ramp up heat earlier to compensate, which is why the curve in peak RoR looks more similar to the 395°F Charge temp profile (red). However, both tipped, and even showed signs of pre-tipping before the end of drying. We saw this from the trier (see the brown spot on the large seed below) at around 300°F on both roasts.
So, we overcompensated for this in our third roast. We step up gas even slower than before -- 10s longer than the first attempt (red) -- and charged 10°F less than the last go at (blue). This profile charge temp was 375°F and can be seen in yellow above. As a result, our peak RoR doesn't even hit 40 but this is a much gentler introduction of heat and we do not see tipping at 300°F.
Now, if we see tipping from here on out, we know that it's because we've kept too much heat later in the roast, not because of our charge or soak. Since we did not, we can proceed going extra fast and keeping gas high much later in our profiling than we might normally. You can see that we keep momentum higher longer in that yellow profile too. That helps us make up for some lost time.
In the end, we drop the coffee and do not see tipping. Success! Had we seen tipping, we would have slowed down momentum earlier in the roast and probably used our trier trick in a different bean temp window to confirm. And, that is our guideline for how to push upper limits on a wetter, more sensitive coffee.
Some ideas and speculating about moderating tipping
One thing to note, inlet / environment temp going into the roast can matter a lot here for tipping. I have this weird idea that keeping the barrel "damp" by limiting airflow in the initial stage helps reduce the amount of tipping in drum roasting. I have not been able to confirm this at all! It is merely a hunch.
However, I think this because coffee releases the most moisture in the beginning, which is now gaseous in the air of your barrel. That air is different than the air that enters the drum later. It has a higher concentrate of water vapor, which I believe can help diminish the application of conductive heat to the outside of your coffee at the early stage in the roast. If you've ever baked, you've probably at one point left water in a pan below to increase the water vapor in your oven to crisp less the outside of your baked good. This is the same idea. (I think) this also should reduce the likelihood of smoking your barrel early on in the roast, during drying.
If you're continuing to tip at really low charge temps and cannot hit the minimum roast length you're seeking, try closing your airflow valve more to increase the starting environment temp to compensate. It's not a foolproof tactic, but it might help you if you have yet to try!
Sensory evaluation
In cupping these 3 roasts, we can clearly taste the acidity, as well as a lingering ash-y flavor. What is most hidden by tipping (we think) is sweetness. It feels like only the bitter (char) and the acid are trying to balance themselves and it is a much less enjoyable experience. Just opening the bucket of these roasts, you can smell which are the tipped by the lack of sweetness and subtle smoke-y aromas. The tipped batches reminded us of dried fruits like prunes (burgundy in color), while the non-tipped batch was more like brighter, fresh fruit (bright red in color).
That's about all we have on this topic. If you don't find the tipping flavor offensive, we actually noticed that the cup reminded us much more of tropical fruit and lime than the other profile. We went with the 375°F charge (yellow) in the end for the Ombligon final profile, but that was just what was best to us. It has bright red, fruit punch character that the other cups did not have. It was very melon forward and had nice sweetness to balance the crazy fruit character.
We sold small amount of the tipped profile next to customers to see what they thought and got similar feedback about "lime", much more acidic, and tropical flavors. We got less feedback about the acrid and ash-y quality, which just goes to show that sensititivity to these things varies from coffee enjoyer to coffee enjoyer.
There is no right or wrong. :) Happy roasting!