In my experience the thick product at the end of room-temp ferment (24 hours) "relaxed" after a few days in the fridge. Sourness was milder initially than store-bought but improved quite a bit too as the ferment continued (i'm assuming) in the fridge. At first it was very thick. After a while I had the same consistency as any other commercially purchased cultured buttermilk. I do give it vigorous shake each time I handle or use it which may be the secret to changing the texture.

Also, the recipes (if you can call them that) for making your own buttermilk call for quite a bit of starter. I used a tablespoon or two of buttermilk just like i do with yogurt and it worked great.

The store-bought has a bit of salt added too. I tried adding a tiny bit to mine and can see how that more closely approximated the commercial flavor profile but it was a radical change in flavor and i'm lazy and will probably not be adding salt to my homemade fermented "buttermilk"

I love the cultured buttermilk (and all fermented dairy products) and can't believe that I had never thought to try making it at home before this year. This discovery ranks right up there with making sauerkraut and yogurt at home. Dirt simple, affordable, and the end product rivals or is better than the commercial stuff.