Can I prevent hot pepper sauce losing heat?

My suggestion is: try simmering the sauce for a short while before storing it in the fridge.

My answer is based on the sauce I use for my Fajitas (onion, assorted peppers, ground cumin and cayenne, cilantro, garlic, and lime juice with honey and butter for a touch of sweetness). It is heated through and coats pulled chicken. This sauce is rather spicy at first and the heat intensifies every day.

Our ingredients are similar with the biggest differnce being cooked vs. not cooked... so, cooking your Pepper Sauce could make all the difference. If you try simmering your sauce, please share the results.

The heat of your condiments isn't actually being lost. The condiments are marrying, meaning the heat becomes more homogenously distributed through the condiment. This means you don't have bits and pieces that have as high a spike in heat than the rest of the salsa, and therefore the condiment is more evenly hot (thought apparently cooler to the taster) throughout.

Pepper or chile sauces use vinegar and oil to retain and even accent their perceived heat. Neither actually increases it though. Vinegar helps clean the palate like strawberries for champagne, or ginger for sushi. It cleans the tongue so the heat can get to it better. Oil helps hold the heat to the tonque and other mouth parts making it seem hotter because it doesn't wash away as easily.

Keep in mind though that pico de gallo is really meant to be made and served fresh. You don't want to give it time to macerate and marry. You want to bite into and taste the individual components of this condiment. Leaving Pico to sit overnight in my opinion really turns it more into a chuncky but watery Salsa.

Hot sauce definitely loses its heat after a while.. though it seems to last longer when there's a layer of olive oil on top, which makes me think that oxidation is playing a role in breaking down the capsaicin, or whatever it is that makes it hot.

I usually do my hot sauce in a very simple way: simply chop the raw peppers (I use Peri-peri), drown them out in plenty of whisky, and pour some olive oil so that there's a layer on top, about a finger thick, when it separates.

This lasts me for a few months (until the next harvest from my Peri-Peri bush), but it definitely loses some of it's punch after a few weeks.

Although this question is a few years old I'll mention that recently I've been getting in to making pepper mash and doing a countertop brine fermentation with my habeñeros. This has resulted in very little loss of heat. I have a batch going right now that's been fermenting for just about one week and surprisingly, it's tasting hotter than when I started it. ¯_(ツ)_/¯

Oil gives the sauce a better flavor but knocks out the heat immediately; I recently discovered this after about five years of tinkering around with sauces. Cooking does not seem to matter. I am still trying to figure out how to keep the heat, and currently trying drying and chopping finely with a coffee grinder.