Reusing yeast cakes questions

I have never reused yeast cakes mostly due to logistical/timing issues but I find myself in the unique position of having a Kolsch and Dortmunder ready to rack to secondaries and have the time and ingredients to make an Altbier and Maibock. The yeasts are White Labs German Ale/Kolsch and Fermentis W-34/70. They have been at 60 and 50 degrees for 14 days. This seems perfect but I've got a few questions:

Do you just pour the fresh wort over the cake and swirl it a few times or is there a need for aeration/oxygenation?

Do you swirl it at all or just pour the new wort on the cake?

Any difference in using a yeast cake for an ale vs lager?

Do you use the whole yeast cake or pour any off?

Any other tips?

Thanks.

The general consensus is that simply pitching onto the yeast cake would result in extreme over pitching. I would either pour out a good amount of the yeast cake and then pitch on it, or scoop some into a sanitized jar and then use that. Check out Mr. Malty's webpage and specifically the pitching calculator yeast slurry section.

I usually grab a cup or two of the cake and put it in a sanitized jar while I clean out the fermenter. Check out the Mr Malty site to determine how much you need.

No need to use the whole cake.

Everyone will tell you something different but I have reused yeast cake 3 times in a row with good results. I made an Oktoberfest (using Cali ale), amber then an IPA, honestly I was just being lazy because I didn't want to have wash and save the yeast, but it worked out great. I just pitched it on top and gave it a good swirl to aerate it

I have pitched on a yeast cake a couple of times, and can't identify any negative effects in the resulting beers with the exception of the possibility of lesser flocculation. Aside from that, I was happy with the result and the process was as simple as it seems.

Overpitching? Yeah, most likely. Did it negatively affect my beer? Not that I can tell.

It was Nottingham.
Dry sachet pitched into a 3.4% mild ale
ESB (6.3%) was pitched onto yeastcake from mild ale.
IIPA (8.2%) was pitched onto yeastcake from ESB.
Yeast went into compost after this

All three brews were great. I fermented in the mid- to upper-range for the mild and ESB, and fermented in the bottom range for the IIPA (for yeast characteristic purposes). Loved them all.

I swirled the yeastcake and created a slurry prior to adding the wort. I did NOT intentionally aerate my wort at any point, nor did I intentionally aerate my yeastcake. Because a yeastcake is most likely greatly overpitching, by the time the yeast is mixed with the new wort, my understanding is that the population levels that are aimed to be reached by the yeast prior to anaerobic fermentation are already present, therefore the lag and reproductive phases are essentially skipped which mostly does away with the oxygen requirement (though, there is a matter of sterol production) and the yeast move right into the anaerobic fermentation. This means that you'll see active fermentation beginning within an hour or three of adding your new wort to the yeastcake.

There is an idea that moving up in gravity when pitching on a cake is good since each fermentation creates new yeast, therefore the population is much larger and higher gravity beers can use that larger population better than lower gravity beers.

If I were to do this again, and I probably will because it worked very well for me, I would split my yeastcake in half after each fermentation. I'd either toss one half if it came from a high gravity beer, or store it if it came from a lower gravity beer. Half of a yeastcake is probably STILL considered overpitching by quite a bit, but at least your reducing how much you're overpitching by.

These were ales and that's how I'd proceed for ales. If I were to do this with a true lager yeast strain then I would NOT split the yeastcake - I would pitch on the whole yeastcake. Lagers typically require a much higher pitching rate than ales and my first time experimenting I would use the whole cake to ensure I don't handcuff myself