About "false" lager yeasts

when we al started learning stuff about beer, someone said that that the differences beetween lagers and ales was that in lagers there was bottom fermentation - that is, instead of the traditional krausen, there would be some kind of "underwort krausen".

but the thing is: from what i've seen in my lager fermentations, that's not what happens. The krausen is still there, top fermenting like any other of my beers.

so the big question is: are the lagers yeasts we're using ACTUAL lager yeasts (s. carlsbergensis) ou ale yeasts (s. cerevisae) modified to ferment between 50 and 60 degrees F with no estery effects?

(just so you know: the only lager yeasts I have ever used are fermentis' dried ones: s-23 and w34/70)

There will always be krausen on top because of the gas released by fermentation. From what I understand (I think I read this in Miller) there was a time when ale = mid-top fermenting yeast and lager = bottom fermenting yeast, but it's no longer that black and white and the strains we use today pretty much ferment throughout the wort.

The main difference today is that ale ferments quickly and at warmer temperatures, i.e., room temperature, and lager ferments more slowly and at low(er) temperatures.

Krausen exists on both types of yeast and now for the most part yeast is active in suspension as there are no real top or bottom fermenting yeast starins.

The real difference between the two types are the type of sugars it can ferment. Lager yeast break down more sugar types and do so at colder tempertures than ale yeast. This is partly why lager brews taste more clean compared to ale brews.

One problem with defining lager vs ale by fermentation characteristics, the breeding and selection process continues. With rare exception, any yeast labeled as a lager yeast will be s. carlsbergensis. Complicating the issue is the many 'lager' kits sold with a clean fermenting ale yeast.

There are top and bottom fermenting ale yeasts. Ditto lager yeasts. Realistically, most fermentations are bulk fermentation with the yeast suspended in the wort.