Can I make a "lager" with ale yeast?

Let me simply reinforce what is being said here with a little more focus on history:

Lagers are not a storage process. They are a product made with lagering yeasts and fermented at lower temps that typically require refrigeration. The vast majority of craft beers are ales, because ales are fermented at room temperatures and are therefore much less expensive to make. If you take an ale and stick it in a cooler, it doesn't suddenly become a lager. Yeah, it sounds ridiculous when you say it like that, but I honestly think that is what some people mistakenly believe.

Rather than get hung up on who made the "first" lager (since no one knows), let us just say that there were a lot of quality improvements in beer brewing in Central Europe in the early 1500's. Most people are familiar with the "Rheinheitsgebot" - the purity law that originated in the duchy of Munich in 1487, and following the reunification of Bavaria was adopted in 1516 and eventually spread, in one form or other, through the entire Holy Roman Empire. This not only defined what beer was, but it limited the ingredients allowed in beer, limited beer profits, and created penalties for brewing "impure beer". However this was before the advent of microbiology, and people didn't understand the science of making beer - they just knew the steps you went through, many of which were extremely ad hoc and random. For example, the original Rheinheitsgebot didn't include yeast as an ingredient because Bavarians either didn't know that yeast existed, or didn’t understand its roll in fermentation. The yeast used in brewing was whatever yeast happened to be randomly introduced to the process, and could vary dramatically from batch to batch, leading to huge variability in quality, particularly in the warm summer months.

Therefore in 1553 the Bavarian Duke Albrecht V simply outlawed all beer brewing during the summer. If they didn't know WHY summer beer was bad, they could at least stop making it. The unintended consequences of this law were two-fold; first, overnight all Bavarian beer became lagers - because only cold temperature lager-making yeasts remained active during the winter months. Second, the last beers brewed in the spring were brewed strong with a higher ABV in order that they had a longer shelf life. These beers, made with cold hardy yeasts, were "lagered" or stored, in cool caves and cellars so that they stayed fresh throughout the summer months. It remained illegal to brew beer during the summer in Bavaria until 1850. Initially people called these winter beers “lagers” because of the cold storage… and it was hundreds of years before they understood that they were significantly different from ales not because of the storage – but because of the cold temperature yeast.

So no, please don’t try to brew something at room temp and call it a lager, LOL! Can you tell the difference? Maybe, maybe not... in the same way that many people can't tell the difference between Kentucky Bourbon and Tennessee Whiskey. However when the product is defined in a very specific way, don't make something else and call it by the same name. If you care so much about lagers, learn how to make a lager.

To the purist, a lager should be brewed with a S. Pastorianus strain of yeast and an ale with S. Cerevisiae strain of yeast. The former ("lager yeast") works at far lower temperatures than the latter "ale yeast") does.

That said, the first lagers (in Bohemia in the 1500's or so) were brewed with whatever yeast happened to end up in the beer. Nobody knew what yeast was in those days, or even that it existed. The term "lager" (as has already been mentioned in responses above) refers to the German word for "storage" (Lagerung) and stems from the fact that this beer style was brewed seasonally, then packaged in sturdy wooden barrels that were stored deep in the cool caves occurring in the region for months on end. During this lengthy maturation the beer fermented out further, cleared, and became somewhat carbonated, which eventually led to beer (esp. later) as we know it today. Until then, beers were brown, murky, flat concoctions served at room temperature.

While using an ale yeast for a later is a vile abomination to the purist, the truth is that quite a significant portion of the micro-brewed beers in the world sold as lagers are in fact fermented with S. Cerevisiae, but using a variety suitable for lower temperatures, in order to obtain a more neutral and "cleaner" flavor profile. Lallemand's Nottingham Ale Yeast (no rebranded to High Performance Ale Yeast) is a good example: at room temperature it's a typical ale yeast giving you a measure of fruity flavors that work well in ales, but at the lowest end it of its wide temperature range (about 10C / 50F or even little lower) and a proper diacetyl rest, it will produce a beer with a flavor profile generally indistinguishable from lagers fermented with a "real" lager yeast.

So the only real question, as I see it, is whether you want a beer that tastes, smells, looks and drinks like a lager and has all the vital characteristics or a lager, or instead you want to make a big think about the pedigree of the yeast you used to brew it. Your choice. :-)

If you call your beer a lager and it's fermented with ale yeast, I firmly believe that it's a blatant lie. In a homebrew setting, who cares, if you're the only one drinking it? As a brewery owner and brewer, I've had many conversations with other owner/brewers that agree. We had a local brewery making nothing but "German Lager" beer and come to find out every thing they made was fermented with US-05. They are were the laugh of the town for a while until they made some changes. My two cents, if you slap a label on a beer that says "lager" and you fermented with an Ale Yeast, you're lying and it's ugly. They are essentially different species of yeast. Saccharomyces pastorianus (or S. carlsbergensis) is your lager strains and Saccharomyces cerevisiae for your ales. It's the same faux pas some make (even more often) by calling their beer a Kolsch and not fermenting with a Kolsch strain and instead using US-05 or something; and if you want to get real technical, should be brewed in Koln, Germany (Americans use the name "Kolsch Style" if they are respectable). Is it a hefeweizen if you ferment with US-05? No. It's only a hefeweizen if brewed with a hefe strain. To sum up, use the right yeast and call your beer what it is.

"to lager" is a process, cold storage conditioning for extended time, usually uncarbed and bulk storage... but the key is cold conditioning to get the effect.

to make a lager, you use lager yeast....but its a homebrew, we can call it whatever we want.

TO fully answer your question, Yes you can lager ale, you can lager beer made with any yeast you want, because you are cold conditioning it to make a crisp clear beer.

one thing to be aware of is, if you bulk lager, and then bottle carbonate...you may need to add extra yeast or give it extra time to carbonate.

If possible on your rig, you could ferment under a bit of pressure. Increased pressure can inhibit ester formation to some extent.

I don't find WLP001, Wyeast 1056 or SafAle US-05 to be as clean and lager-like as many people claim. They give a slight peach and/or circus peanut ester even at cold temperatures. Instead I would recommend Wyeast 1007, 2565, or WLP029 altbier or Kolsch-style yeasts for extremely clean lager-like ales.

Technically, a lager should be called a "lager" if it's made from lager yeast and lagered like traditional methods. In reality, you can use Safale US-05 at cool temperatures and extended cold aging and 95% of people wouldn't be able to tell the difference between a traditional lager and an ale fermented at cool temperatures.

Just call it whatever you want because that's what I see at many local breweries around me.

You can make great tasting beer with any method that works.

Can you ferment California Ale yeast at low temps and make great tasting beer? Yes.
Can you not make a lager and call it a lager? Thats up to you.

But can you make spaghetti and meatballs with ziti? No.
If it tasted great I'd still ask for more.

But it's homebrewing you get to do whatever you want.