[Community_garden] coffee grounds are HIGHLY acidic

[Mike McGrath]

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: <yarrow at sfo.com>
To: <community_garden at list.communitygarden.org>
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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