[Community_garden] coffee grounds are HIGHLY acidic

Tue Feb 20 16:02:30 EST 2007

OK--so this agrees with Wood's End. Anybody find a 'neutral' source other than the Washington State one?
                                        ---McG
  ----- Original Message ----- 
  From: Steven Garrett 
  To: Mike McGrath ; Ray Schutte ; community_garden at list.communitygarden.org ; yarrow at sfo.com 
  Sent: Tuesday, February 20, 2007 3:58 PM
  Subject: Re: coffee grounds are HIGHLY acidic

  Here is an answer: http://www.food-info.net/uk/products/coffee/acids.htm

  The pH of coffee is 4.9 to 5.2 (the same as beer, but less acidic than rain in the NE). For further comparison, lemons are around 2. Thus, coffee is not HIGHLY acidic, but rather MODERATELY acidic; as food (or rain) goes. As soil goes, 5.0 is HIGHLY acidic, so you probably you don't want to add straight composted coffee grounds to alkaline loving plants.
  Steven

  Mike McGrath <MikeMcG at PTD.net> wrote:
    OK--everybody who drinks coffee and has a pH meter; can you please do a 
    little home testing of your daily grounds and report back in?
    ---Mike McG

    "Two men say they're Jesus; one of them must be wrong."

    ----- Original Message ----- 
    From: "Ray Schutte" 
    To: "'Mike McGrath'" ; 
    ; 
    Sent: Tuesday, February 20, 2007 11:44 AM
    Subject: RE: [Community_garden] coffee grounds are HIGHLY acidic

    I have been using coffee grounds along with selected browns as a mulch for
    years. I have my soil tested regularly and have not found an acidity
    problem here in the Pacific Northwest know for a certain level of acidity.
    I have found the following to be trustworthy.

    Starbucks commissioned a study in 1995
    to better understand the make up of the
    organic matter we call coffee grounds. The
    following is the result of the analysis
    performed by the University of Washington,
    College of Forest Resources:

    Primary Nutrients
    Nitrogen 1.45%
    Phosphorus ND ug/g
    Potassium 1204 ug/g
    Secondary Nutrients
    Calcium 389 ug/g
    Magnesium 448 ug/g
    Sulfur high ug/g
    Terms: ND = indicates sample is below
    detection limit
    ug/g= microgram / gram

    Most of the acidity in coffee is removed
    during the brewing process. Used grounds
    have an average pH of 6.9. Use your
    grounds within 3 weeks to capture the
    most nutritional value.

    Ray Schutte

    "The truth of the matter is that the flower has cleverly manipulated the bee
    into hauling its pollen from blossom to blossom." The Botany of Desire,
    Michael Pollan

    -----Original Message-----
    From: community_garden-bounces at list.communitygarden.org
    [mailto:community_garden-bounces at list.communitygarden.org] On Behalf Of Mike
    McGrath
    Sent: Tuesday, February 20, 2007 6:42 AM
    To: community_garden at list.communitygarden.org; yarrow at sfo.com
    Subject: [Community_garden] coffee grounds are HIGHLY acidic

    My bad! I was one of the people guilty of spreading the 'coffee grounds are
    neutral' news for several years; luckily, I eventually followed up with more

    research. Wood's End Lab has confirmed that coffee grounds are VERY acidic;

    here's the very interesting details:
    http://www.gardensalive.com/article.asp?ai=793
    Best to all, Mike McG

    ----- Original Message ----- 
    From: 
    To: 
    Sent: Monday, February 19, 2007 10:10 PM
    Subject: Re: [Community_garden] Lime, worms and flies

    > Don wrote:
    >>Interestingly, coffee grounds would do the opposite of
    >>lime chemically, making conditions too acidic. But
    >>worms don't like them, either - I did an experimental
    >>trial of large amounts of coffeegrounds as sole
    >>foodstock, with newspaper as bedding, in wormbins, and
    >>the results were a complete bust (small amounts of
    >>grounds are fine).
    >
    > Acidic coffee grounds? That's a common myth. In fact, although coffee
    > itself is acidic, used coffee grounds are neutral.
    >
    > _____
    > http://faq.gardenweb.com/faq/lists/soil/2002015354019975.html
    >
    > While it is widely thought that they are acidic it has been shown
    > that most of this acidity is removed in the brewing process. Used
    > grounds are essentialy neutral and composting them with other
    > materials will buffer any minor residual acidity.
    >
    > One of the forum regulars with a scientific background did some
    > controlled chemistry experiments on the acidity question and this is
    > what he had to say:
    >
    > "Roasted coffee is fairly acidic, but it appears that almost all of
    > the acid is water soluble and is extracted during brewing. Used
    > grounds have essentially neutral pH, although the coffee beverage
    > produced is rather acidic.
    >
    > The measured pH of used coffee grounds was 6.9, with a significant
    > amount of buffer capacity - adding the coffee to either acidic or
    > basic solutions drove both towards neutral pH. The exact pH of used
    > grounds will depend on the pH and alkalinity of the water used in
    > brewing, but with any potable water, used grounds will be close to
    > neutral pH."
    > _____
    >
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  Steven Garrett, PhC, MS, RD
  Ph.D. Candidate, Social and Environmental Geography
  University of Washington and
  Nutrition Education Evaluation Specialist
  Washington State University

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