How to calculate the amount of harvest yeast into next batch?

[Shaft]

I agree with @Slid . I've always harvested yeast simply. With a decent slurry, I fill 3 or 4 sanatised jam jars half way, then top off with pre boiled water which has been left to cool. I chuck them in my beer fridge and use 1 per next 30 litre batch after removing the water top layer (usually always via a starter, but on occassion just pitched straight). It's never failed to take, although sometimes a little slower to kick off Vs a new bought yeast. I've even used yeasts that have been 4 or 5 months in the chiller, with no issue.

I generally make East Coast PAs or wheat beers, occasionally an English Bitter.

 

[cushyno]

Everyone's experience will differ. It depends if you're interested in getting the most healthy yeast into your wort at the right levels to ferment well and produce the right esters for the style, or if you're simple after reusing yeast to produce drinkable beer at low cost.

While the two aren't incompatible, considerations for each come with different priorities.

Mr Malty is a great resource if you're prepared to read through. It expands what you might not want to overpitch, why you'd build starters of different sizes, density of yeast, and others interesting nuggets of info:

Pitching:Http://www.mrmalty.com/pitching.phpStarter FAQ:Http://www.mrmalty.com/starter_faq.php

 

[Tuizner]

I am currently trialling a harvested batch in a Belgian tripel. Harvested and washed (preboiled and cooled water) MJ M47 (i know its a dried yeast but from it comes liquid...). I try to tip off the yeast from the trub from one jar to another. The end result was 160g of yeast/water of a consistency somewhere between pack yeast and wort - so I reckon it maybe equates to just over a 50g pack of liquid yeast. Pitched into 15L of 1080 tripel. Nothing for 12 hours but the following day the bubbles were going well and building up to a crescendo day 2. Possibly underpitched but not an issue for belgians where we like the esters.

Will report back with any FG figures.

I also did another batch on the same day but really underpitched (35g) and so added a dried pack of crossmyloof belgian... Will see which one works out better in a week

 

[RawAbility3]

Interesting experiment, would like to see the results.

 

[Tuizner]

Interesting experiment, would like to see the results.

So..... the batch with the mix of CML dried plus harvested yeast plodded on for 8 days and finished as expected at 1018 And tastes fine.

the batch with the larger amount of harvested yeast went much faster but failed on me at day3. Stuck. Had to make a starter with whatever I had around - another CML Belgian dried. Slow to restart but back running at day 5. Finished at day 9 with a similar 1018. Tastes more yeasty but I hopped higher bitterness so will be fine and the yeast will settle out After a few months.

conclusion - may just stick to dried