TL;DR: Quick Symptom Check

• If the cake barely rose, and is dense in flavor/texture: suspect weak or expired baking powder/soda (or incorrect amount).
• If it rose too fast, domed, then collapsed, and the middle is gummy: suspect too wet of a batter and/or that the center never fully set.
• If the edges look done, but the middle has sunk: suspect your oven temp, hot spots, and underbaking.
• The most reliable doneness check is internal temperature: many cake styles are done in the 200–210°F (93–99°C) range (blog.thermoworks.com).

What “sunk in the middle” means, and why it happens

A sunk center nearly always indicates a structure problem: the batter rose into the oven (air + steam + chemical leavening), but the cake’s internal structure didn’t set firmly enough to hold onto that rise as the cake cooled. Oven temperature and how bubbles expand and set are a large part of the story. (foodnetwork.com).

When you’re weighing (1) expired/weak leavening, (2) excess liquid, (3) oven issues, look at the pattern of the rise and the texture of the center, not just the crater when you slice in.

Fast diagnosis: 3 questions to narrow it down fast:

1. Did it rise much at all? If it sat there dense and low, think leavening (expired, wrong type, or wrong amount).
2. Was the center still wet/gummy when cool? If yes, then consider underbaking and/or a too-wet batter (either due to excess liquid, or sugar in the recipe plus wet add-ins, which release moisture).
3. Do you trust your oven temp? If you don’t verify it regularly with an oven thermometer, suspect it regardless, and take “oven issue” as likely.

Cake Symptom Diagnosis Table

Cause #1: Expired (or weak) baking powder or soda, and how it looks and how to prove it

Of course, chemical leaveners can lose their “pop,” especially post-opening, so that the batter rises less to the occasion when it meets the heat. That tends to show up as a cake that has never risen adequately in the first place (almost short and dense) rather than one that rises highly, then collapses, (simplyrecipes.com)

Cause #2: Too much liquid—why it creates a sunken, dense center

A batter that’s too wet for the size of its flour/egg frame may seem to be rising ok, but will often collapse into an unbaked area since it can’t cook rapidly enough through the center. The edges of the cake can be set, and the middle hangs there without enough support from waffles to stay afloat until it’s done baking. So…it sinks in place, or after you take it out of the oven.

• Clues it’s excess liquid: if the centre of your cake is shiny or gummy. You may also see a slightly dense “custardy” line toward the middle; or, the edges may be over done before the centre looks done.

Big suspects for unintentional liquid givers: Really big eggs; milk/water “to thin it out”; huge pieces of juicy fruit, thawed frozen fruit no chance at draining (drain it!). Or adding syrup or sauce or succulence of any kind without reducing another liquid. Pan size can mimic “too wet”: if you use a smaller pan than the recipe calls for, the batter is deeper and the center sinks lower before it sets.

How to prevent excess-liquid collapse (practical fixes)

1. Weigh ingredients when possible (especially flour and liquids). Measuring cups are easy to misread.
2. If you’re adding a wet ingredient (puree, yogurt, citrus juice), reduce another liquid to keep the overall hydration similar.
3. For fruit: toss fresh fruit in a little flour; for frozen fruit: thaw, drain, and blot before folding in.
4. Bake in the correct pan size. If you must change pans, expect a different bake time (and use temperature to confirm doneness).
5. Don’t “fix” thick batter by adding liquid unless the recipe explicitly says to; thick batter is often correct for certain cakes.

Cause #3: Oven problems—temperature accuracy, hot spots, and underbaking

An oven that runs too hot or too cool is a common cause of sunken centers. Too cool, and the cake structure sets too slowly; too hot, and the outside can set before the center is ready, with the middle unable to support itself. (foodnetwork.com)

Stop guessing doneness: use an internal temperature target

Many cakes are done when the center reaches roughly 200–210°F (93–99°C), with lighter cakes often finishing a bit higher than heavier ones. This is more reliable than waiting for a perfectly clean toothpick, which can push the cake toward dryness. (thermoworks.com)

• If the cake sank AND the center is under-temp: it’s primarily an oven time/temperature problem (even if your recipe is fine).
• If the cake is at temperature but still sinks badly: look harder at recipe balance (too wet), leavening amount, and mixing method.

A simple troubleshooting workflow for your next bake

1. Before baking: confirm your leavener is active (quick bubble test) if it’s old or has been open for a while. (simplyrecipes.com)
2. Preheat fully: give the oven enough time to stabilize after it beeps (many ovens preheat before they’re truly steady).
3. Bake on the center rack with the pan centered (unless your recipe says otherwise).
4. Avoid opening the oven early: wait until the cake has visibly risen and looks set on top.
5. Start checking doneness by temperature near the recipe’s minimum time (aim for the appropriate target range). (thermoworks.com)
6. If your cakes are inconsistent batch to batch, verify oven temperature with thermometers in multiple spots.

For more details, including rescue techniques: (kitchenaid.com)

Don’t blame a “too wet” cake (unless you really did make it too wet or nasty oven)

Insufficient mixing: there can be a “too wet” zone resulting from “weak” structure—the cake didn’t build the necessary structure to rise properly, leaving crumbly or gumminess (quite possibly cause by the cake collapsing due to a lack of structure) somewhere in the batter. Undermixing is a legitimate issue and can be a problem, especially when bakers are attempting not to mix too long (as noted, easier to do so with people often saying ten and twenty mix time). (kingarthurbaking.com)

• Stick to your mixing times (time at least once so you know what “2 minutes on medium” feels like), also. (kingarthurbaking.com)
• Be sure to scrape the bowl and paddle/beaters; a pocket of dry flour stuck to the side can create weak spots.
• And, if you used a different kind of flour (like instead of cake flour you used all purpose flour, or maybe gluten-free blends) be prepared for a different absorption and structure to the batter.

How to tighten the cake that flopped? (So it isn’t wasted and you aren’t super disappointed)

• If not really flat (just falling in, baked): even the top and take pride in how cute the dip is, spray frosting in and may gobs, or fill the hole with fruit or whipped cream on top.
• Then you are able to fit it back in the oven (lower temperature and tent with foil), until the middle of the cake reaches the right range; it might have a dense texture though, very heavy and yolky. You will be a master of kitchen mixes!
• You can take it and turn it into a “trifle,” just cutting it out into little cubes and splitting cream/custard, and fruit. The texture wouldn’t really make that much difference! Or, also make into cake pops or crumb crust to dry it out, by crumbling it up and sauce on and projected on point.

Your baking powder is past its prime. Is it dangerous? Well, no… but your cake might be flat. Usually, this is a performance/quality issue, not a safety concern. The bigger problem is that it may not lift your cake well. That said, if you’re still not sure and can’t find a stronger expiration date on the container at hand, do a quick hot-water bubble test and replace if weak.

Why do cakes fall? The most obvious reason is that the leavening expired prior to baking. Not a hard and fast rule, but leavening that’s been around the block, maybe the back of the pantry and into tomorrow is not ideal. A rise-and-collapse show for the ages more typically points to the cake not setting up quickly enough (too low of temperature in the oven) and the outside burns and sets while all the delightful air bubbles flow freely in a gully of goo in the center. Result? Fill a heavy batter pan with just a smidge more than half and hope for a miracle.

It’s hard to pick a best test; everybody seems to think their method is, well, the best! But according to ThermoWorks, one solid way to know that sure cake pull is good or bad and avoid the dreaded sunken center is through internal temperature confirmation. Most will finish around 200°F (93°C) to 210°F (99°C) through bread cake and sweet cake styles and targets. Not too high, not too low for an ideal result, thermally speaking…but the only rule of thumb there is that there are no hard and fast rules, only the proper kind of golden brown. Anyway, open the darn oven and check the internal temperature next time! Not too shy too, because that bouquet from the heat curl of the oven fan and hood above is frosting unto itself.

From there, it’s all feedback from ThermoWorks that suggests lightly digging blind into dough before serving. Be careful with the mix! Avoid undermixing–a vague medium pasta mix that drives through the cake batter and maybe like sound–“floury and crumbly” batter makes cake perilous…but the wrong oven temp speaks volumes. Is your oven hot-spotting? Hazarding the time near the end of the bake to snake a tool near the cake…did you crack open the oven door ahead of the legend of the sunken city? “I promise I only opened once.” Tempting one to wise up and other.