What is the difference in flavor between a fermented pickle and a vinegar pickle?

Pickled vegetables using vinegar brine contain vinegar as a main acid. It is somewhat sharper than the mixture of different acids produced by the fermentation method. Here you have vinegar, lactic acid and other chemical byproducts of happy life of your culture including a little amount of alcohol (though this process is done with air access, unlike making alcohol, where there must be no oxygen present, or your alcohol making turns into vinegar production).

1. vinegar brine method: Vinegar is the main acid. The taste is sharper compared to fermented pickles thanks to acetic acid which is present in most white vinegars.It differs depending on the recipe and amount of salt, sugar water and spices. It is the more stable way to preserve and gives more reliable results with little expertise. Results vary mainly season to season from the vegetables' quality (flavours and texture) You can use different types of vinegars from different processes (apple cider vinegar, wine vinegar) and shift the flavour of your results. It's a very tasty way of preserving vegetables. There is some loss of vitamins due to heating, but your product lasts longer.

2. fermentation method: The process requires better knowledge of precautions, methods, and combination of ingredients. The flavour is more fruity due to the combination of more different acids and a little alcohol and other products of the culture. It's less sharp, and also depends on the length of process, temperatures, and qualities of the ingredients. So generally this process is more "colorful" in result and more unpredictable. To get reliable results you have to master the process. Imagine it like master wine makers. This method preserves vitamins, but products are best kept in the fridge or cellar and the shelf life is shorter and depends on for how long your mix will stay alive. Otherwise you would have to sterilize it in later stages and destroy vitamins.

In summary: Flavour is different, because different chemicals are present. Vinegar pickles have vinegar; fermented pickles have vinegar and other flavours.

I've been fermenting for quite a while (everything from sauerkraut and kimchi to Indian-spiced grated carrots and kohlrabi spears with dill), and my two cents is that the flavor of fermented pickles is vastly (vastly!) superior to that of vinegar pickles. Fermented pickles are indeed fruitier and more complex. When I have the first taste of something I've just fermented for the first time, I'm almost always surprised and pleased to the point of involuntary smiling and "mmm"-ing. It's just pure joy.

Most importantly for me, fermented vegetables taste more like vegetables than those pickled in vinegar. With vinegar pickles, I now find the vinegar totally overpowering, even just when opening the jar. I feel like I'm eating processed food. Fermented vegetables taste closer to fresh.

Another fun thing is that fermented pickles continue to mature with time. I usually keep my ferments at room temperature for one to two weeks, then move them to the fridge. The cold slows the fermentation way, way down, but it doesn't stop it completely. If you make 5 pounds of sauerkraut and consume it slowly over, say, two months, you can bet that your last serving of it will taste quite different from your first. But it's always good.

It is absolutely worth the extra effort to go the fermented route. It's an adventure in deliciousness. Here's a site with some great recipe ideas: http://www.picklemetoo.com/recipes/.

Another vote for lacto-fermented over vinegar! To me ferments have more complexity, especially in that lingering aftertaste. But I would say that since the lactobacillus is technically digesting the food before you do, the textures can be less crunchy which is an issue for some.

Fermentation, as a side effect, alters proteins releasing free glutamates: umami.

Monosodium glutamate (MSG) [...] is naturally occurring at high levels in some foods. The enantiomeric composition of free glutamate was examined. Foods to which MSG was added had a high total level of MSG but a lower relative percentage of the D-enantiomer (usually less than 0.8%). In comparison, fermented foods tend to have high relative levels of D-glutamate but a lower total amount of the amino acid. The relative percent of D-glutamate in nonfermented foods containing no added MSG was also found to be low compared to fermented foods.

https://www.ncbi.nlm.nih.gov/pubmed/7915127

Just tried them today, I dunno what these people are talking about but they are not pleasant off the bat.

The ones I got contained no sugar so had a slight acid (really mild compared to vinegar) and salty flavour, I mean I dunno what I expected since cucumbers don't have much flavour ether.

I always had this idea of pickle juice in my mind and burgers when I think of pickles, vinegar is the way to go for this type of experience, much better flavour.

It does pair well with some smoked vegan cheese, I could see me getting used to the flavour but it does not have anything drawing me back for more.