Water

The idea that medieval people drank beer because they did not have access to safe drinking water is a complete and unfounded myth.

To quote Steven Harris and Bryon L. Grigsby in their book Misconceptions About the Middle Ages:

“There is no specific reason then to believe that people of the time drank proportionately less water than we do today; rather, since water was not typically sold, transported, taxed, etc., there simply would have been no reason to record its use."

There are plenty of articles out there discussing this topic.

Small beer/ale (the type of beer drunk regularly in the Middle Ages) had a small alcohol content, typically less than 1% and never more than 3%. This would have had some anti-bacterial effect, but in given the life-span of small ale in the Middle Ages (it was usually drunk as soon as it was ready with little to no ageing process) I doubt it would have had too great an effect on the liquid's propensity to spoil (See Jack's link in comments on alcohol affect on bacteria over time). As a brewer of regular strength beer, I can tell you that some bacteria will infect a barrel of ale just as readily as a barrel of water.

Having said that, small ale in the medieval period was on some level less likely to make the drinker ill, solely for the fact that the water/wort used to make the ale was boiled before fermentation.
But this pales in comparison to the real reason small ale was drunk in such quantities in the Middle Ages:
Medieval people drank small beer because it was a great way to squeeze as many calories out of their grain as possible. Off-cuts of stale bread, spare unusable grain were all 'recycled' back into small ale in an attempt to fuel a hungry population.

Without the invention of small ale/alcohol, medieval society would simply just continue drinking water, but in larger quantities. The two articles I have linked do a good job of explaining this, and if you want to make water safer in your world, just make boiling it more prevalent. It is already theorized that medieval folk knew that boiling made water safe through holistic means, just didn't know why :)

Brew a nice cup of tea.

People all around the world found and used all kinds of herbs and other plants with antibiotic properties since prehistoric times. Popular examples for Europe and North America include sage, mint and blueberry. Adding parts of the plant to cold water not only flavors it, but also kills bacteria in the water. But the antibacterial properties might not be enough, so you want to boil the water first.

The disadvantage of tea is that it spoils a few days after brewing, so you always have to make it fresh.

Even in neolithic times people probably had the tools to boil water and cook a soup by lining a pot-sized hole in the ground with leather, filling it with water and putting a hot stone from the fire into the pot.

If you're hunting or travelling and do not have the time or the fire to brew tea, first drink the (untreated) water and then chew the herbs.

Yogurt (etc)

Milk contains lactose, also known as milk sugar.
There are bacteria that ferments this into lactic acid.

Depending on exactly which bacteria and what else you do with it, you get a lot of different products from yogurt to cheese. Wikipedia has a list. (Not all of these are drinkable, but many are)

Goats were the first domesticated milk giver. Cows and sheep soon followed. Check Wikipedia's List of Domesticated Animals for details.

Note that people who can't digest lactose have no problem with lactic acid.

Vaelus pointed out in a comment that these bacteria can process other sugars too. This means that in a world without any no alcohol-producing yeast, grain and fruits would ferment into lactic acid instead.

(Spicy) Soups

Spices have been used around the world, but particularly in hot countries, for their antimicrobial properties (food spoils more quickly in hot weather) for thousands of years.

A soup or broth made with some of the more antimicrobial herbs and spices (the source linked above suggests garlic, onion and allspice are particularly good, as well as the more widely known capsicum) would be sterilised by boiling, and the spices would probably work to keep it safe for a couple of days after cooling down (remember that until the introduction of hops, beer could only be kept a short time too).

Another advantage of this process is that a wide variety of herbs and spices - with a range covering most of the planet - have antimicrobial properties, so such an approach would work be feasible even in places that don't have a suitable climate for growing certain plants (e.g. tea, as suggested above).

Blood.

http://basia.typepad.com/india_ink/2007/09/got-blood.html

Many cultures drink the blood of livestock. Currently the Maasai are the ones famous for it, but horsemen throughout history drink the blood of their horses. If you have big tame animals around it makes sense. Blood is sterile when it comes out. The animals can spare you some now and then in exchange for your good care and concern. Blood is very nutritious. Plus as opposed to milk, male animals can contribute too.

However, microbes that do some other reaction are acceptable.

no need.

Just as beer can be made in almost any part of the world, the replacement beverage must be easily producible worldwide, with Neolithic technology.

you can bleed an animal with a sharp rock.

Just as beer resists spoilage, the replacement beverage must have some sort of chemical makeup that keeps it germ-free relative to pure water.

The immune system of the animal keeps it germ free.

Just like beer, it must be palatable to humans. Acquired tastes will make it delicious.

from above source:

I know I'm looking kind of bug-eyed in these photos, but it actually
wasn't that bad. It was very thin and bland. It tasted just like human
blood. (Not that I'm in the habit of drinking human blood. But if
you've ever cut your lip or had a tooth bleed, you know the taste).
There was actually very little taste as I was drinking it, but for
several minutes afterwards I had strong blood aftertaste.

carbonated malt beverage

So, your two societies — the hunter–gatherer types and the agrarian types — don't have any naturally–occurring way to obtain alcohol in their foodstuffs. Disregarding, for the moment, how exactly that can be, let's consider the other aspects of the question.

You are looking for a beverage which — correct me if necessary

• Is sourced from a malt of grains and other starchy foodstuffs.


• Is prepared using such techniques that do not involve metalworking nor any undue labor or time.


• Is prepared in a way which sterilizes the water so as to kill any microbes which either cause disease or which produce waste products noxious to health.


• Contains a substance that renders the beverage unsuitable to the future growth of any such microbes as per the stipulation listed above.


• Is itself not hazardous to health — at least not in quantities that are necessary to satisfy the requirements of adequate hydration.


• Is not seriously unpalatable. Not an ipecac or anything like that.

Running through various possibilities, I wonder if something like aqueous carbon dioxide could be made tenable?

First, you'd have an aerobic reaction which converted most of the sugars to carbon dioxide and water.

Carbonic acid would retard the growth of most disease–causing micro-organisms and would not affect the flavor of the beverage all too much — indeed, many people like the tingly effect, and it is otherwise almost tasteless.

It would be much like non-artificial soda water: Sodium carbonate was dissolved in a solute of subterranean water which then emerged from springs; it was long believed to possess various health benefits — many of them probably exaggerated, of course.

The one problem with this is the solubility of carbon dioxide in water. Because it doesn't precipitate out in a sludge, which can then be dissolved again, you eventually lose the carbon dioxide through effervescence, or evolution, out from the solution. This would decrease the acidity of the beverage if it was not tightly sealed.

If necessary, I could go through the equations which demonstrate how the solubility of carbonic acid changes with temperature and pressure, and how that changes the pH of the solution. I will summarize with this: the only difference between that and a solution of ethanol — i.e. carbonated beer — is that you wouldn't have any ethanol remaining to retard the growth of unwanted microbes in the beverage.

We can get around that with two other properties of the microbes:

• They act on starches just as well as they do on sugars. They need to ferment sugars also, but if they produce enzymes that assist them in attacking the long poly-saccharides chains of starch, then they can begin their work when most other microbes — such as bacterial deleterious to human health — haven't had an opportunity yet.


• They don't need to completely ferment all the sugars in the malt beverage prior to imbibing it. The slurry can be ingested — although it would pay to not drink it immediately if you wished to avoid very unpleasant gastrointestinal pains resulting from the carbon dioxide being released.

Further considerations regarding the microbes:

• These microbes would need to be much less specialized than any occurring on earth. Not only would they break down starches, but the sugars resulting from that. Furthermore, their rate of fermenting the starchy slurry would be increased chiefly by aeration — mixing in air.


• To make them easier on the human gastrointestinal tract, simply have them encyst or die at a pH more acidic than their home solution of carbonic acid and within the normal peptic range — somewhere around 1.9 should do the trick.

Kefir or Kumis

Kefir and Kumis are drinks made from fermented milk. Beer may have been ubiquitous among sedentary populations, but in the steppes, there wasn't much in the way of grain. Instead, most of their food game from their herd animals, in the form of meat, milk, and blood. Just like with beer, fermentation happened at some point, and this new drink became popular (I mean, who doesn't like booze?).

As a bonus to whomever may be lactose intolerant, the brewing process breaks down most of the lactose into lactic acid, which shouldn't give you as many stomach problems.

Kombucha

Basically fermented mushroom tea tea fermented with a combination of yeast and bacteria. Similar brewing, fermentation, health/calorie traits to beer, but essentially non-alcoholic.

Kefir. In addition to the kefir grains (yes, they are actually blobs that you filter out and reuse and they multiply while doing their thing) used to ferment milk, there are also kefir grains used to ferment sugar water. They are not interchangeable and creating one from the other is not easily done.

Water kefir, as it's called, is just as easy as regular kefir. You throw some kefir grains into your liquid and let it sit for a couple of days, then strain out the kefir and start again. You can also do secondary ferments to get a nice fizz going.

For water kefir, you need literal sugar water or you need a liquid that has sugar in it, like juice or coconut water. Juice and etc are common for secondary ferments. If you use them too often with primary ferments, the kefir grains might permanently stop growing and/or producing. But it's not hard to fix that in a community of kefir makers.

Similar drinks to kefir, like kombucha, are pretty straightforward as well. Others have elaborated on them. I also agree with the statement that water was too dangerous to drink is a myth.

Aside from the fact that alcoholic beverages taste and feel good, the main reason people drank them in quantity was for nutrition. Fermentation produces lots of Vit C and B vitamins, probiotics, and more. Modern beer has none of that because it's filtered and pasteurized, etc. Non-alcoholic ferments will have similar nutritive value.

Revised: I'd say fresh juices, like apple juice. There are many medieval or neolithic ways to press for juices; in the end it is just pressure.

If there are no bacteria that eat sugars, then I'm not sure the fruit would rot as fast, or rot at all. Apples can have a waxy skin that retains moisture, and if no bugs are eating the apple, then the water in it has been very well filtered through the apple tree itself. Also the pulp after pressing still makes for good animal feed, e.g. chickens and goats.

Grape juice and orange juice can provide drinkable filtered liquid, too.

All of these juices can be filtered to remove solids and stored in natural pouches, including animal bladders and stomachs, which is how primitives have carried liquids before. If there are no bacteria that eat sugar, then they will likely not go bad; other than the sugars, without any solids, there should be no caloric content to exploit.

I will take exception to the notion that beer tastes delicious, I hate it. I'm not opposed to alcohol, but beer sucks. Hard cider is good, so is wine and liquers.

You do know that the vast majority of natural ways to get high involves a medicinal plant in one way or another, right?

If you are too vegan to lick a toad and think that ecstasy and other synthetic stuff is too industrialized for your tadte, here are some options for your greenhouse:

• Coffee. See this video from Cracked, 4:55 onwards to see how to prepare real coffee.


• Poppies. America's number 1 addiction problem (not counting alcohol) has to do with opioids. Think of that.


• Salvia. Legal in the US and UK today. If you are into neo-spiritual [be nice].


• Grass. Not the lawn variety.


• Tobacco. Legal drug everywhere, but everyone only wants to smoke it. It can be used in other ways.


• Jimson. Not to be confused with Ginseng.


• Coca.

All of the above can be served in tea. Making it hot will kill germs, just like alcohol would do at room temperature but more efficiently. The last one in the list is also perfect for sodas, for those with a kink for history. Each will have their own extra effects... Some will make you happy for a while, some will clear your mind and ideas, coca helps ignore pain and hunger and tobacco soothens the tremors a psychonaut will get from doing too much of the other items in the list.

I am including only those that are easy to plant or to get in most places. Peyote doesn't grow everywhere, and betel is not a thing in the West.

Finally, as for being germ free... Just use fresh plants to make fresh tea! You don't throw away a good apple just because it has no alcohol in it, the same goes for the plants above.

If you must have a germ-resistant concotion then, stick with coffee, but cook ground beans in a leather bag for a few days before mixing with water and serving. Only the good germs will survive. This is a drug the ancients took to go berserk, so be careful.