Mashing Grains In A French Press For Yeast Starters

Pilsner malt mashing in my French press

Pilsner malt mashing in my French press

After brewing the Saison earlier this week, I had about a pound of leftover Pilsner malt that was just staring at me.  I didn’t have much use for it, so I was going to simply toss it on the compost pile.  But then I remembered the expired packet of Munton’s generic ale yeast I had in the fridge.

About a year ago, I thought about using my French press to mash grains for yeast starter wort.  I thought the idea was pretty brilliant, but I never got around to trying it.  It makes great coffee, and the process for mashing grains is almost identical.

The idea was simple; I’d use my teapot to heat the strike and sparge water, and mash the grains right in the French press’ glass decanter.  Then I’d use the screen plunger to strain the wort from the grain.  Assuming a rather paltry efficiency of 55%, I plugged some numbers into Beersmith, and estimated I could get about 1000 mL of wort with a starting gravity of about 1.045.

So how did it go?

The Good:

After the mash; ready for sparge

After the mash; ready for sparge

  • I definitely made fermentable wort!
  • Using pot-holders to insulate the glass decanter worked pretty well.  I only lost a few degrees during the 1-hour mash.
  • The mesh screen eliminated the need to vorlauf.
  • The yeast fermented vigorously, despite being more than 18 months past its expiration date.

The bad:

  • My actual efficiency was even lower than I expected.  The starting gravity was only 1.038, indicating an efficiency closer to 45%.
  • The fine mesh screen clogged almost immediately, and made it difficult to drain the wort out of the decanter.
  • I was only able to collect about 650 mL of wort instead of the anticipated 1000 mL — probably due to the clogged screen.
Visible fermentation after about 90 minutes

Visible fermentation after about 90 minutes

Overall conclusions:
This method absolutely works in an academic sense, but fails at being an efficient means of wort production.  It’s definitely simpler to boil a little DME and be done with it.  But that’s not nearly as much fun.

I like that the scale of the French press is perfectly suited for making just enough wort for a yeast starter.  However, the biggest problem is the fine mesh screen.  It clogs too easily, and prevents the wort from being able to filter through.  I was able to squeeze out more wort by firmly pushing down on the plunger, forcing the wort through the screen.  Unfortunately, had I actually intended to use this starter wort, the excessive pressure on the grains probably resulted in excessive tannin extraction.

I still think this idea could work with some modification.  The mesh screen is the main problem.  If the original screen was replaced with something more coarse, I think this could work pretty well.  I’m going to see what I can find at the hardware store, and I’ll probably run this test again.

I can absolutely confirm that the French press makes truly excellent coffee.

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12 Responses to Mashing Grains In A French Press For Yeast Starters

  1. Sean says:

    I’m the founder/moderator for Punk Domestics (, a community site for those of use obsessed with, er, interested in DIY food. It’s sort of like Tastespotting, but specific to the niche. I’m interested in growing the home brewing section, and I’d love for you to submit this to the site. Genius!

  2. Sean says:

    What a great idea to use a French Press for mashing grains!!

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  4. Fletch says:

    Grains, as you know, are cheaper than extract, so don’t give up because the mesh clogged. In the future, just mash on the stovetop and pour the whole concoction over a strainer into your starter vessel. If a couple of bits get through, it doesn’t matter. They’ll settle in the starter vessel or in your primary vessel.

    • Ryan G. says:

      Yeah, I really want to try this again when I’ve put a bit more thought into it. I decided to try this on a whim, and the entire process was done pretty hastily. I think that instead of trying to force the plunger through the grain bed, it would have worked better if I had simply let gravity pull the wort through the grain bed and mesh screen. If nothing else, the glass decanter and potholder setup held temperatures really well. So I definitely like using it as a small scale, starter-sized mash tun.

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  6. Betsy True says:

    I’m finding needle point canvas comes in several different meshes. There might be one for you. I have no idea about the food safe-ness of these products, but some are plastic and some are fiber. I used some fine mesh to make a greek yogurt strainer.

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  8. Don Osborn says:

    Funny. I was thinking of trying this and your blog came up on a Google search. Couple of thoughts. Your comment on the efficiency being lower makes sense. This is kind of like a “no sparge” batch. Since you are not sparging, you are leaving more sugars in the grain. (I suppose you could pour some 170 degree water in there an do a little sparge. You would have to account for this in volume and gravity thoughts). I’m a little confused by what you mean by the grains getting caught in the mesh screen. Don’t you just plunge it down and the liquid stays on top and you pour it off? I will have to try with mine. Regardless another commenter has a point: you could just dump the whole thing into a hop/grain bag and set that in a strainer over a pot and see what you get. I like this idea because it would be cheaper than buying DME and like you say, it could be fun. But you would have to have some spare time. 🙂 Cheers.

  9. Don Osborn says:

    I was also going to add, to save some time I would just do a half hour mash. By that time you will have gotten by far most of the sugars out of the grain you are going to get. There have been experiments done on this. You might even be able to cut it to 15 min actually but 30 would be pretty safe.

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