Spirits are not "made", they are cooked. Can gin be overcooked? Oh yes, it certainly can.
Anyone who has ever accused me of "making spirits" has heard my rather aggressive response. Spirits are not made, they are cooked. Like any fine food product, gin is not just whipped together in a chemical formula, it is ingredients that are cooked together based on a unique recipe. The difference being that spirits often take months to cook properly in multiple stages and the equipment used is as much a part of the recipe as the ingredients.
So to answer that burning question, yes a gin can most definitely be overcooked. I would go so far as to say this is one of the most common mistakes made in craft gin making today. Once you learn to identify the characteristics of an overcooked gin, you'll start to find it more often than you would think.
The key to cooking a good gin is not just selecting the botanicals, but in understanding how their flavours and oils are released. One of the things I love about cooking up a batch of gin is smelling and tasting the differences throughout the process. When the batch first comes to the boil, the heavy juniper oils are the first things out of the still. So heavy in fact, that I bleed that first bit off and don't add it to the final gin. That captured bit goes in a special tank to be added to the next batch. It will eventually cook into the gin, but not the first time through the still.
Once the heavy oils are removed, the strong juniper (earthy) comes through and the coriander is quick to join in. After a few hours, the citrus and acid notes arrive changing the character entirely. As we carry on a few more hours, the light fruits and eventually the florals of the heather make themselves known. Then near the end, the lighter juniper notes, the more menthol tones, arrive in a burst.
Finally, the output turns over to a more bland mixture of residual flavours. Once again, these aren't included in the final product but are saved for redistillation in the next batch. The saved liquids are known as feints, and although not particularly exciting on their own, without redistilling them into each subsequent batch, a gin never quite reaches its full potential.
So overcooking? The key to a good quality gin is to keep it low and slow. The reason it takes me all day to complete a batch of gin is because I never get the still hotter than it needs to be. Just enough to gently boil the liquid and produce the merest drip at the output. Similarly, I use a vapour infusion method, where the actual botanicals are not boiling away in the pot. Instead, they are suspended in the column of the still where the vapour runs through them gently extracting flavours and oils. In my opinion, gin botanicals are far too delicate to be haphazardly boiled away in the pot.
Some distilleries go so far as to use low-temperature vacuum stills to extract the more delicate flavours. It's an interesting approach that I've considered using at some point. My issue is that such methods often are used to distill each botanical separately, with the final gin being 'painted' together from multiple distillations to get the flavour profile desired. I'm not entirely against this approach, in fact I've tasted many excellent gins made that way. Maybe I'm just tied to my method of cooking a gin as a complete dish.
So how do you know if a gin is overcooked? That's pretty simple, just sniff it. You've probably noticed that juniper is actually two botanicals in one. There's the heavier earthy vegetal aspect to juniper, and then there's the much lighter fragrant almost menthol-like element. The heavier earthy element is what you get on the nose and tongue from an overcooked gin. It usually means the distiller was rushing things to fit more batches in per day, or maybe they just don't like spending all day on a single batch. No matter the reason, if your gin has that heavy juniper taste and smell, odds are good that it was overcooked.
The coriander often comes across a bit soapy in overcooked gin, although that can change based on where the coriander was sourced. North African coriander tends to be very soapy if even a little bit overcooked. Central European coriander is so nutty that the soapiness only comes through if it is terribly overcooked. And Indian coriander, well to be honest, I don't think it is well suited to gin making at all. Don't get me wrong, it's perfect for your curry or other dishes on the stovetop, but I'm not a fan of it in gin.
Finally, in overcooked gin, I find that the citrus notes tend to be sharper and err on the sweet side (cook any citrus long enough and you get marmalade). And the floral notes tend to simply disappear into the heat.
So next time you try a new gin, be on the lookout. Is the juniper slanted towards the vegetal end? Is the coriander a bit soapy? Citrus gone a bit sharp and the florals all but missing? You might be tasting an overcooked gin.