Mile High Spirits Fireside 6 Year Old Single Barrel Bourbon (Hazmat Proof) Review

I’ve already written extensively about Mile High Spirits’ many whiskies over the last 4 years. They have impressed me so far with their quality and the fact they continue allowing their spirits to age. This is not as common as you’d think. Many new distillers regulate how old they will allow their products to get – like New Riff for example – they never allow their standard bourbon and rye whiskies age past 5 years. Why is that? So that they can build up their older stocks for sustained future releases. Other times, distilleries decide that their early distillate needs some adjustments, so they don’t allow their first barrels to continue aging if they don’t think the juice will be worth the squeeze.

But Mile High seems to have confidence in their distillate’s maturity – plus it looks like they’ve set enough back to continue having older releases year after year. I’m just curious when they will run out because surely it can’t last forever!

Today I’ll be tasting one of their newer releases that was sent to me in December last year (hence the Christmas theme of these pictures; oops!). It’s a 6 year old bourbon with a very unique trait – it’s bottled at 141.2 proof!

How does a whiskey gain proof and why did this one get high?

One of the stranger things I’ve noticed over the past few years is just how many distilleries are popping up with Hazmat proof whiskies (defined as being above 70% alcohol by volume). This is unusual because the proof will have to rise as it ages. And the starting proof for Bourbon or American-made rye whiskey to enter the barrel higher is 125 proof. That means the whiskey will have to gain at least 15 proof points during maturation. That’s no easy feat!

So how does a whiskey gain proof? The simple answer is that more water needs to evaporate inside of the barrel than alcohol. Science-minded people might point out that alcohol’s boiling point is lower than water. Wouldn’t that mean that alcohol is more susceptible to evaporation then? Maybe, but a molecule of water is smaller than a molecule of alcohol (ethanol if we’re being specific). So it is actually the alcohol that has a harder time escaping through the wooden structure of a barrel.

In the real world, barrels typically rise in proof due to fluctuations in humidity in comparison to heat. There seems to be a specific correlations to the range of heat and humidity that are needed to make proof increase or decrease, but frankly, I don’t understand it that well. Just know that my observation is that barrels aged in very low humidity regions (like out west where Mile High Distillery is located) tend to rise in proof as they age.

I’ve experienced 130+ proof barrels from Mile High in the past, but never any this high. I assume it was aged on the top rick of Mile High’s 6-rick tall single-story warehouse (similar to Four Roses), but that’s about all I can speculate on.

The experience of Hazmat Bourbon

For the most part, whiskies with high proofs will mellow out the longer they’re allowed to age. A good example of this is Elijah Craig Barrel Proof batches that are above 135 proof. I’ve drank almost all of them and can confirm that after that many years in the barrel, the bourbon does not have the burn that the proof on the label tells you it should.

If you’re new to super-high proof bourbon, let me tell you how to drink them. The first rule of thumb is to pour your whiskey and let it set for 15-30 minutes. This usually gives enough time to allow some of the more volatile notes to evaporate. Next, imagine the kind of sip you normally taste and cut it by half automatically. Heck, cut it by a quarter if you really want to play it safe.

For the first couple sips, it’s okay to swallow it quickly. After doing that, you can take longer pauses between each sip to let your tongue acclimate. Finally, if you find that it’s still too hot for your palate, let the bottle set open without the cork on for an hour. Then seal it back up and put it away for a few weeks. Sometimes the extra exposure to air will help dull the whiskey. There have been cases where I took an empty (clean) bottle and split a very high-proof whiskey into two parts and let them rest with that headspace for a few weeks before coming back to them.

Mile High’s bourbon is only 6 years old, but to me, that’s right around the threshold it should start to mellow out. So let’s see how it does. I sampled this neat in a glencairn.

Tasting Notes

Nose: A fiery wall of ethanol makes me check myself before putting my nose that close to the glass. Oops, I guess that’s a rule I should have covered in my section on how to drink high-proofed whiskey. Anyway, once things settle down, I’m starting to pick up on rich caramel and chocolate scents. There is a ton of cinnamon for spice, but if I’m being honest, sometimes it’s hard to distinguish if it’s cinnamon scents that are stinging my nose or the ethanol. If I had to sum up the nose with a specific food/drink, it would be Mexican Hot Chocolate.

Palate: Baking spices hit my tongue first (after the ethanol simmered away a few taste buds) while burnt caramel, chocolate and peppermint join in the fun. The chocolate and caramel combine for almost a “Tootsie Roll” type flavor. Most Mile High Spirits bourbon has a high-rye profile to it, and I’m still picking up on it with each sip. Herbal notes accompany orange extract and oregano. Tannins come courtesy of oak and leather and also include a bit of earthiness to the mix.

Finish: The heat doesn’t really let its foot off the gas, even on the finish. The sweetness of caramel and chocolate are still there and there is an upswing in the level of richness that gets left behind as the sip fades away. Baking spices, and some residual ethanol, create a warmness that stays with you the whole time. Kind of like a Kentucky Hug, care of Denver, Colorado.

Score: 7.5/10

This is a big bourbon that delivers big heat. There’s no trying to avoid it either. Six years is a good start, but needs more age to calm it down. I could feel all 141 proof points with every sip. But since I’m used to higher proofs, I felt like it only took a few sips to calm down enough for me.

One of the highlights of the dram was how rich the finish became as I was drinking it. I wasn’t expecting it, but it was a welcome treat. Usually high proofed whiskies strip so much of the “coating” on your tongue away, it’s almost impossible to determine a mouthfeel after a while. That didn’t seem to be the case with Fireside’s Hazmat Proof. I liken the richness to eating a piece of decadent chocolate candy.

Final Thoughts

Hazmat whiskies are a novelty that have developed a cult following among enthusiasts. I will be the first to admit that when I see a Hazmat whiskey – or even one that comes close to it – that I’ll buy it for the experience. A mean trick is to mail a sample off to a friend. You’re treated to your own personal episode of Fear Factor before doing the reveal!

Hazmat-level bourbons and rye whiskies aren’t for everyone, but they do have their worth. They’re interesting conversation pieces and a good way to test your endurance. That’s why I have no issues recommending bottles like this to buy. I think that people do seek these out for the novelty that they are. It’s just a bonus that this one happened to have a really great finish to boot. As for Mile High Spirits, it’s just another notch in their belt for unique bottles coming out of Colorado.