Skip to main content

Harvesting Berliner Weisse Bottle Dregs

Some background

It’s been awhile since I posted but I’m back and should be on a regular posting schedule. I’ve haven’t been brewing a ton in recent months but I’m trying to build up a stockpile of beer as I have my first child on the way and I’m guessing that I’m going to run short on brewing time. With that said, I picked up a beer that caught my interest recently and text on the can really caught my interest. The beer in question in a Berliner Weisse from White Birch Brewing; review coming soon(ish). The can said:

Our ales are unfiltered, unpasteurized, and traditionally made…

What does that mean? Well it means that their beer has not had all of the yeast and bugs stripped out of it from filtering or pasteurization. Why is that good for me? It means that I can harvest yeast from the bottom of the can, pitch it into a starter, and eventually use it to make a full blown beer. Awesome.

 What is yeast harvesting?

As I mentioned above, yeast harvesting is the process of taking dormant but still viable yeast from the bottom of a bottle or can. Generally, beers that are not pasteurized or filtered or bottle conditioned have yeast mixed into the beer. The yeast can generally be found on the bottom of the bottle of the can as dormant yeast will fall out of the beer and lay on the bottom.

How to harvest yeast

Harvesting yeast is super easy, but there are some precautions that need to be made. I’ll go over my process below as well as give you the quicker version. The number one thing that you want to be concerned about is making sure that you sanitize EVERYTHING. If you have brewed before, you should know the process.

Step 1: Setup your mash/malt

For yeast harvesting I generally like to make a starter from the harvested yeast. The main reason for this is that there is not enough yeast in the bottom of a can or bottle to properly ferment 5 gallons of beer. When I make a starter, I’m shooting for .75 gallons.

For this yeast starter I wanted to make a mini version of the end beer that I wanted to brew. The main reason for this is so that I could test brewing in a bag. I started off with a scaled down malt bill of my original beer recipe. I put .6# of pilsner malt and .3# of wheat malt into the grain mill. You can see how little grain there really was (note this is a six gallon bucket)


Step 2: Sanitize

 After my malt was ready to go I sanitized a one gallon jug with some PBW and then StarSan. I wanted to make sure that nothing was left living inside of the glass container except for the yeast that I would eventually add.


At the same time I had a bowl filled with StarSan and I placed two cans of my donor in it. The goal here is to kill anything on the outside of the can as the yeast will touch the outsides on its way out during a pour. I also had an airlock, drilled stopper, and a funnel in the bowl.

Step 3: Mash/Boil/Brew in a Bag

As all of the important stuff was sanitizing, I prepared for a brew in a bag (BIAB) attempt. My first ever attempt at BIAB. I knew that I wanted to end with .75 gallons of liquid and my calculations showed that gain absorption and boil loss would account for .15 gallons. So I placed .90 gallons of water into a small stock pot and brought it up to 148 °F.

As the water heated I placed my BIAB bag over the pot and waited for the temperature to hit the magic number. For my BIAB I used a simple nylon paint straining bag found at Home Depot for $3.


Once the water hit my desired temperature I poured the grain into the bag and stirred to mix up any dough balls. The basic concept here is that I didn’t want to mash .9# of grain in my normal 10 gallon water cooler as the thermal loss would be too significant. I also didn’t want to clean my mash tun for such a little job. BIAB allows you put place the brewing grain and water into the brew pot and mash while in the pot. The 148 °F magic number is where I wanted my mash to rest for an hour. I placed the bag in once the water hit temperature and monitored it for awhile until I dialed my stove in to stay at 148 °F. At this point I let it rest at that temperature for an hour.


After the hour was up I picked up the bag, let it drain of liquid and tossed the grains in the trash. The bag was cleaned and saved for future brews. I turned the temperature up on the stove so that I could get the wort to a boil. A 15 minute boil was all I wanted I just wanted to kill whatever might be in the liquid (I know, I know. 15 minutes isn’t enough to kill everything, but it’s enough to give my yeast the upper hand).

Post Boil

It’s a pretty typical situation at this point. I cooled down the wort, which happens incredibly quickly with only .75 gallons of liquid, and readied my fermenter. Once I got the wort down to 70 °F I emptied the sanitizer from my gallon jug, placed the funnel on it and poured in my wort. I then took the two cans of beer, opened them, and pour 3/4 of them into a glass. The final quarter left at the bottom was swirled and dumped into the glass jug. I then shook the jug to try and get some oxygen in there for my little yeast buddies. Once I was done I got something that looked like this:



I took the jug into my basement and placed it in a box to protect it from light (there was a small amount of hops in this on scale with my recipe). The hardest part of harvesting yeast is seeing if what you did actually saved them. I waited for a few days to see if it worked because I honestly forgot about my starter. About three days after brewing I got this:


Fermentation had clearly happened and my yeast buddies were still at work. This starter was allowed to sit for another day or so (thanks work) and was pitched into a full scale version of this beer over the weekend. I’m not sure how much of the souring critters made it as they take some time to show-up, but if they are in there, they will grow.

I’ll get a recipe and such up shortly but harvesting yeast is not difficult. The quick and dirty version is below.

Quick and Dirty Version

I have described the easy way to do a yeast starter previously. You can find it right here but the basic idea is that instead of doing a mash, you use malt extract as your base and boil a mini beer from there.