I can answer this one!

Let’s start off with a discussion about sources. Academic historians have done some interesting work about the history of brewing. Take for example Ale, Beer, and Brewsters in England: Women's Work in a Changing World by Judith M. Bennett of University of Southern California. It’s an excellent history of the role of women in early modern brewing guilds and how they were pushed out. A lot of the academic history of brewing is in this vein, very solid stuff but focused on the social and economic aspects of brewing with very little attention paid to the actual beer that’s getting brewed. There’s just nearly zero academic interest in things like the history of evolving beer styles.

So where are we going to use as our sources? Breweries? Nah, information put out by breweries is written by marketing hacks who don’t know the first thing about history and often spread long-debunked ideas. Journalists? Again no, they just don’t have the time to dig deep into the subject and divide the truth from the legends and journalistic articles about brewing history are often riddled with errors.

So, if the academics don’t care and other people don’t know, then what sources can we use to answer this kind of question? In general, with when looking at the history of beer styles your best bet is amateur researchers. People like Ronald Pattinson, Martyn Cornell, Lars Marius Garshol, and others have done simply enormous amounts of primary source research (or in Garshol’s case, a huge amount of fieldwork) and really really care about things like how beer tasted in the past. For this answer I’m going to be drawing on Ronald Pattinson’s research which largely involves going to breweries and taking thousands of photos of their brewing records and then posting about what he finds on his blog (barclayperkins.blogspot.com). Don’t let the amateur appearance of his blog fool you, the guy’s done an absolutely mind-boggling amount of primary source research including teaching himself a half-dozen languages just so he can read brewing records in more languages and he’s regularly hired as a consultant by breweries to help them develop historical recreation beers.

OK, with all that out of the way, what can I tell you about small beer? Well first off let’s look at why people in the 18th century (and much earlier) were brewing beer so weak. Not ALL of what was called “small beer” was quite as weak as what you’re talking about, but a lot of it was. They generally weren’t brewing beer so weak because they wanted weak beer but because they were poor.

That sort of incredibly weak ale was often made by using spent grains (the leftover grains that you have after brewing) with just a little bit of fresh malt added. You’d get a little maltose out of the fresh malt as well as a tiny bit that you can squeeze out of the reused grain. Depending on how desperate you were, you could keep on reusing that malt until it got pointless and you’d feed it to the pigs (spent malt is fine as part of an animal’s diet and many people make dog biscuits out of it and peanut butter but there were issues later on with urban dairies having cows that were ONLY fed spent malt which caused horrible malnutrition both in the cows and in the babies that were fed this, often adulterated and infected, milk). This very very weak beer was often not made by professional brewers but by people at home, sometimes with spent grains gotten from professional brewers.

This sort of homemade weak beer because less of a thing later on. Malting and brewing techniques became more efficient so that brewers got better at getting all of the maltose out of the grain. This was helped along by brewers starting to use hydrometers (little floating bobs that measure how dense a liquid is) which allowed them to get actual data on how efficient their processes were which caused radical changes in how brewing was done. This made it more and more pointless to try to squeeze an extra tiny bit of maltose out of spent grains by reusing it after the brewers were done with it. Also, with the rise of cities, fewer poor people had the space or equipment needed to homebrew so that declined a lot. The other thing to note here is taxes. During the Napoleonic Wars there was a large increase on malt taxes and later on in the 19th century there were no taxes on beer per se but instead rather quite high taxes on malt (until the Free Mash Tun Act of 1870) so you couldn’t avoid alcohol taxes by making your own beer which removed one of the main economic reasons for brewing by poor people. Also, while you could pop by your neighborhood guild brewer as ask to please use their left-over malt, that sort of neighborliness didn’t really apply to 19th century industrial breweries. I mean just imagine what would happen if I walked up to the gates of a modern Budweiser brewery and asked for a bucket of their leftover grains.

For quite some time many rural estates would also brew their own beer for their own use, including incredibly strong majority ale (ale brewed after a son was born that was then drank when he officially became a man) and much weaker brews for the farm laborers. This also gradually declined with the rise of capitalism and malt taxes.

So homemade weak beer that had been popular for a very long time dried up in the 19th century but that doesn’t mean that all kinds of week beer died out, some were still produced commercially they just weren’t called “small beer” anymore. But these kinds of weaker brews were very much a sideline. The 19th century saw the rise of industrial-scale brewing for the first time and if you were going to turn beer into a profitable commodity you didn’t want something so cheap that it wouldn’t be worth the price of transporting it. You’d also want beer that wouldn’t spoil. Porter was great for this. Early porter (which tasted NOTHING like modern porters) had plenty of hops (which are preservative), a decent amount of alcohol (which is preservative), and brett yeast (which consumes dissolved oxygen and leftover carbs better than other strains of yeast). Porter kept so well that brewers in the earlier chunk of the 19th century would age it for extended periods of time in ENORMOUS wooden vaults, they were so big that when one burst the beer flood killed people. Porter was also famously cheap enough for working class people to afford.

So, while porter was king (until the rise of mild and then bitter and then other beers later on) brewers DID brew other beers and some of those could be incredibly weak. Generally, these weaker beers, instead of being made separately like in the old days, were just more normal beers watered down after mashing. For example here you can see a list of the strengths of various beers in 1835: http://barclayperkins.blogspot.com/2008/09/ipa-strong-beer.html The strengths are in Original Gravity (i.e. how dense the wort is before you brew it, to compare to modern beers Budweiser has an OG of 1.044 but is fermented a lot drier than 19th century ales so you get more alcohol out of it with the same amount of malt). As you can see there were some quite weak beers kicking around. Throughout the 19th century a lot of quite week beers were marketed under various names but most commonly “table ale.” However, there wasn’t that much of a market for this lower alcohol beer because the customer didn’t save money by drinking a lot of it instead of less but stronger ale.