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I stopped drinking but I have a lot of stale beer. Is it ok I pour out all this beer for raised beds? It seems as it is mostly water and yeast. Has anyone have any anecdotal experience with this?

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    As a general rule of thumb, just because something is "mostly water" doesn't mean it's good for your plants. Stomach acid is mostly water. So is herbicide (usually). – csk Mar 3 at 16:33
  • Beer is usually fermented right up to the alcohol tolerance of yeast. I'd expect multicellular plants to have a lower tolerance, as do people. – Wayfaring Stranger Mar 3 at 17:42
  • @WayfaringStranger That is definitely not the case in the UK. There is no particular problem fermenting up to 14% ABV without using special yeast or concentration techniques like freeze-distilling, but almost 80% of beer sold in the UK in 2018 was below 5% ABV and only 2.6% was above 6% ABV. (Source: assets.publishing.service.gov.uk/government/uploads/system/…) – alephzero Mar 3 at 18:46
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    Beer is reputed to be an excellent fertilizer, but the usual method of using it is to drink it first and then apply what is left after the alcohol has been filtered out :) – alephzero Mar 3 at 18:50
  • @alephzero I used to make my own. That's what I did, and it would definitely kick your butt to the curb. In the States, we have this stuff called 3.2%. It is impossible to get drunk off of. You're right though, beer does vary quite a bit, but we multicellular Eukaryotes tend to be more sensitive to alcohol than single celled Eukaryotic yeasts. – Wayfaring Stranger Mar 3 at 20:55
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I wouldn't recommend it, not least because it will stink... plus every slug and snail for miles around will be heading for your garden, they love beer - it is often used to create slug traps. The yeast content is not particularly helpful either - see here https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/using-beer-on-plants.htm#:~:text=Two%20ingredients%20in%20beer%2C%20yeast,seem%20like%20a%20good%20idea.

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If we compare with for example the use of other complex liquids as irrigation candidates such as human/animal urine, dilution seems to be an approach that works. For urine the recommendation is dilution 10 times by volume. Soil type and the specific crop that the diluted product will be used on are also important. For example potatatoes, corn and squash can use diluted urine once they are established as crops. Beer might be easier to handle than urine since the alcohol is only about 3%, and once diluted that would make it 0.3%. Maybe set up a few pots of target plants and try out a test solution to observe the effect on growth, with test and control samples so that you can tip the plants out of the pots to examine the condition of the roots.

Update: There is an article in ASHS "Root-zone Alcohol Is an Effective Growth Retardant for Paperwhite Narcissus" which discusses some experiments done with non-diluted alcohol products of various kinds, including beer, on plants. There is some speculation about why beer in undiluted form would be unsuitable for watering based on sugars present in the beer which would encourage the wrong sort of bacteria for growth, but this avenue was not researched specifically. The whole point of fermenting beer is to convert sugars to alcohol. However not all sugars are susceptible to fermentation - dextrose, maltose and sucrose yes, but lactose not. I guess someone will have to pursue this a bit further to discover how much sugar remains in beer once fermentation is complete. From my own brewing it is clear that once fermentation is complete the gravity is less than 1 indicating very low sugar, but clearly you can still taste the sugar when drinking.

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  • I'm dubious about the biochemistry of this. Plants are natural producers of small amounts of ethanol, not consumers. Unlike urine, ethanol contains zero NPK which are the principal plant "fertilizers". Ethanol also degrades to acetic acid which is used commercially as a herbicide. (The transformation of ethanol into acetaldehyde and finally acetic acid is what gives you a hangover!) – alephzero Mar 3 at 19:03
  • I'm no chemist, but beer is known as liquid bread and setting aside the alcohol and water components the remainder will have some interesting nutrient content. The concentration of alcohol is very low. Regular use of alchohol on leaf tissue to clean insects and their residue seem to have little detrimental effect. The downside being unknown is why I suggested the experiment on potted specimens first. – Colin Beckingham Mar 3 at 20:10

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