So I'm not beer historian, but I do have some observations on how traditional beer is produced and consumed that might be useful. Mods, if this falls under the "no anecdotes" rule, let me know and I'll take it down.

Prior to modern professional beer brewing, brewing was mostly done as an extra income source by housewives (Bennet 1996). This is still the case for some developing countries (Roe 1981, Lobnibe 2016). I am most familiar with the brewing of a sorghum beer from northern Ghana, called pitu or pito (it's not an English word, so best guesses on how to spell it.)

A quick summary of how I observed pitu being brewed is as follows, with relevant photos [here] (https://imgur.com/a/g6uNR3x): Grains of sorghum are wetted and allowed to germinate, after which they are crushed by milling (Image 1). The crushed grains are then mixed with water and boiled over a fire for about two hours (Image 2). Following boiling, the mixture is added to a large bowl with cool water, which both dilutes and cools the mixture (Image 3). Once it cools, the mixture is strained to remove the spent grains and then added all together into a large cauldron (Images 4 & 5). The spent grains are either used as animal feed or as mulch. Yeast is added to the sugary solution in the cauldron in the form of a lump of sourdough starter. The pitu can be drunk at this point (Images 6 & 7), before the fermentation gets far along, or it can be held off for a couple days to allow the alcohol levels to rise. If you drink it early it’s referred to as “soft pitu” whereas later, it will be “hard pitu.” The flavor of the pitu is similar to a fruit beer. If you’ve ever had a mango beer, the flavor isn’t be too far off. The carbonation bubbles are much less prominent than in bottled beer.

In terms of the science for how to consider the quality of the beer, a major difference between how this beer and modern beer is consumed is that pitu and other small beers are meant to be drunk within a couple days of being made. Modern bottled beer is intended to be stored for significant amounts of time in bottles or cans, so any contaminant would have more time to produce toxins and off-flavors that would negatively affect the beer. I would say that this is the biggest difference. Indeed, the addition of hops to beer, begun in Europe in the Medival Period, but not standard until the 15th century, provides preservation that allows beer to be stored for much longer periods (Sakamoto & Konings 2003).

EDIT: If you want to try making something similar, try out this recipe of Sumerian beer: https://anthrochefblog.wpcomstaging.com/2018/01/22/sumerian-beer/ And if you're interested in food history, his podcast is a great one!

Sources:

• Bennet 1996 Ale, Beer, and Brewsters in England: Women's Work in a Changing World, 1300-1600 Oxford University Press.
• Roe 1981. "Who Brews Traditional Beer in Rural Botswana? A review of the Literature and Policy Analysis." Botswana Notes and Records 13:45-53 https://www.jstor.org/stable/40979633
• Lobnibe 2016. "Drinking pito: conviviality, popular culture and changing agricultural production at the rural–urban interface in Brong Ahafo, Ghana." African Geological Review 37(3):227-240 https://doi.org/10.1080/19376812.2016.1253489
• Sakamoto & Konings 2003. "Beer spoilage bacteria and hop resistance." International Journal of Food Microbiology 89(2-3):105-124 https://doi.org/10.1016/S0168-1605(03)00153-3

For wines, there are several chemical factors that contribute to chemical and microbial stability. Acidity, sugar, alcohol (particularly in the case of fortified wines), and the use of sulphur. Sulphur treatments may have been known to the Romans but that knowledge was lost until it was rediscovered by the Dutch in the mid 18th century (Johnson 1989).

The only modern wine that most likely resembles Roman wine is Madeira, which has the distinction of being the most stable of all wines once opened (a bottle will remain largely unchanged for several months once opened). This is due to its high acidity, low pH (wine is a buffer solution), and relatively high residual sugar as well as the process of deliberate oxidation to which it is subjected.

The Romans appear to have used a number of techniques to ensure the high sugar/acid/alcohol characteristics that ensure stability in addition to deliberately oxidative techniques that under the right chemical circumstances “toughen” a wine (Johnson, Halliday 1992). For the finer wines or wines from the best sites, the would dry the grapes on the vines by tying off the stems of the grape clusters, thereby cutting off the cluster’s access to sap from the vines, halting ripening. This was done before the grapes reached phenolic and chemical ripeness, ensuring a high total acidity; the drying would concentrate what sugar had developed ensuring a potential alcohol around 20 percent, possibly higher. Techniques like this are still used to this day in some parts of Europe, notably to produce Amarone (in which the grapes are dried on straw mats for 1-3 weeks prior to vinification) (Johnson 1989).

The other technique employed to achieve the same result was to boil the must, which was presumably done for wines from sites that did not merit the labour intensive practice of tying of clusters (Johnson 1989). The grapes would still have been picked at a time that modern wine makers and modern palates would consider much too early, but the early picking had the advantage of preserving the acidity and the boiling served the function of removing some of the water thus concentrating both the sugar and acidity.

Regardless of how the sugar and acidity levels were achieved, the vinification process was the same: fermentation in a buried pithos or dolium (large amphorae). Fermenting in buried vessels had the advantage of providing a measure of temperature control/stability. Racking was gravity fed and a deliberately oxidative treatment (Johnson 1989).

The resulting wines were probably dark brown (fermentation on skins for the creation of dark red wines is a very recent innovation in terms of the history of fermented grape juice) from the oxidation, rather sweeter than most of the wines commercially available today (think a cheap Californian moscato), but with a lip-smacking acidity that would balance the sweetness, and smelled of nuts and raisins in the best examples, and of rubber and rot in the more common wines (Johnson 1989).

These wines would not suit most modern palates, and it’s possible they didn’t suit most ancient Roman palates as spicing the wines was a very common practice (Johnson 1989). These wines, as you can imagine, were probably not the most enjoyable to drink, but the combination of low pH, high TA, high sugar, and the deliberate oxidation produced wines of remarkable chemical and microbial stability that travelled very well and were probably capable of aging with tremendous longevity had the Romans used suitable containers to do so.

Sources: The Story of Wine (1989), Mitchell Beazley/Octopus, London, UK

The Art and Science of Wine (1992)