What is of more relevance is the quality of the beer.
Most authors agree that Rastrum was brown to dark brown, sweet, cloudy and tended to go sour or even stinky fast. It is just one version of the omnipresent Braunbier (brown beer).
Of cause it was top fermenting and it was fermented in wooden vessels that could stand in a cellar or over the ground without any cooling even in the summer.
In the book "Die Kunst des Bierbrauens" (the art of brewing beer) published 1771 in Dresden, Johann Christian Simon explains how to make better beer.
He explicitly refers to the lame leipziger "Rastrum" which should be improved.
he counts 6 reasons for differences between the local beers:
1. climatic differences
2. location of the brewery
3. differences in season and weather
4. different materials used in brewing
5. differences in water
6. different procedures in malting, brewing and fermenting.
He does not know that there are different yeast strains, as he thinks of fermentation as a chemical process. Nevertheless he knows to point out what can cause spoilage and how to keep the wooden vessels and apparatuses clean. He also knows the word "Hefe" and about its importance for fermentation but not about its nature and breeding characteristics.
He advises to bring the wort to a temperature of 25°C to 35°C depending on the ambient temperature.
He also knows that too much or too little yeast is bad.
He knows that top-cropped yeast ("Spundhefen") is the best yeast. (189)
He gives the valuable advice to try the yeast with a small portion of wort before pitching it into the full batch, instead of just checking its smell.(192)
Even his hints for yeast-storage seem acceptable (put them in a stone-bottle, close it with tar-pitch and bury it in the ground at a shady place or plunge it in a cool well) (193).
But what if we have to get fresh yeast? Wheat flour, hops, egg white, honey or sugar? Porridge, wine, juice of sweet fruits, sourdough or rye flour?
There might be a reason for his belief that after every fermentation the brew will go sour - there is only the option to slow that process down.
He knows how to keep beer unspoiled is to make the barrels tight by pitching them and by storing them in fresh cellars or ice-caverns.
He also says that bottled beer is three times stronger and better in its spirit (carbonation) than beer that has fermented at the air. (205-6).
He also describes how to produce Ice-Bock in order make a strong and durable beer (210)
Düsseldorfer Alt might be the one beer of our time that comes closest to the old Braunbier.
some hints how a leipziger Rastrum might have been:
- color: brown to dark brown
- sweet, rel. low in alcohol
- can be well hopped (esp. in the summer)
- funky fermentation or sour (a good one was not too sour or funky)
- Fermented in Wood, conditioned in pitched wood or bottles.
- can be cloudy or clear (a good one was clear)
- Yeast can be everything from wild yeast, bakers yeast or german ale yeast.
- spices and salt are possible, maces, nutmeg, cloves, juniper and citrus zest were quite common