In an excellent post about Native American cuisine, /u/Reedstilt suggests that the Ojibwe ate a lot of maple sap products:
Maple syrup takes a crazy amount of energy to make using modern methods, and sugar all the more so:
What process did the pre-European-contact Ojibwe use to manufacture maple sugar and syrup? How did they tap the trees? How did they collect the sap? And above all, how did they remove the water?
Pre-European sugaring methods have been heavily debated, since native groups took on the use of metal kettles very quickly. On this question, I'd recommend checking out the following (open-access) article:
Holmes and Egan set out the ethnographic information:
Ethnohistorical documenntation of techniques. - References to sugar making using prehistoric methods and utensils are either sketchy, inferential, or late descriptions under circumstances when metal cauldrons were not available. The statement of a Kickapoo chief is, however, often cited (e.g., Henshaw 1890; Nearing and Nearing 1970) as adirect account favoring prehistoric sugaring. He said:
Can it be that thou art so simple as to ask me such a question, seeing that the Master of Life imparted to us an instinct which enabled us to substitute stone hatchets and knives for those made of steel by the whites; wherefore should we know as well as they how to manufacture sugar? He has made us all, that we should enjoy life; he has placed before us all the requisites for the support of existence, food, water, fire, trees, etc. Wherefore then should he have withheld from us the art of excavating trees in order to make troughs of them, of placing the sap in these, of heating the stones and throwing them into the sap so as to cause it to boil, and by this means reducing it to sugar? (Keating 1825).
Stone boiling as described by the Kickapoo chief is commonly inferred to have been the method used prehistorically because pottery or wood containers are considered unable to withstand direct heat (e.g., Nearing and Nearing 1970). Other sources, however, do state that direct boiling over the fire was possible so long as pottery was covered by wet clay or birch barkvessels placed only over coals (H. Smith 1933:93; Nearing and Nearing 1970:20).
Freezing is also frequently cited as a method employed by the Indians to reduce the water content of the sap to produce syrup (Havard 1896; H. Smith 1933; Fernald and Kinsey 1958). Freezing of the sap in shallow containers allows the thicker sugar concentrated sap to settle to the bottom while a layer of ice, which can be easily removed, forms on the top.
From these and other references it seems that sap can be processed in vessels made of pottery (H. Smith 1933; Nearing and Nearing 1970; Densmore 1974, 1979), birch bark (Armstrong 1892; Havard 1896) or wood (Keating 1825; Havard 1896) and that evaporations accomplished by stone boiling (Keating 1825; Havard 1896; Fernald and Kinsey 1958), direct fire (H. Smith 1933) or freezing O. Smith 1831; Havard 1896; Fernald and Kinsey 1958). Additionally, a combination of vessel types and/or techniques may be used. (pp. 63-64)
Holman and Egan decided to experiment whether these suggested pre-Contact sugaring methods could efficiently produce sugar. This was a first try, and they made many mistakes such as burning one of their birchbark containers, but even with their mishaps, they achieved good results, enough to show that sugaring without metal kettles was completely possible, backing up traditions of pre-contact sugaring.
It should be noted that other scholars responded to their article by saying that proving how it could be done doesn't mean it was indeed done, and there's continued vehement debate over finding historical texts supporting early sugaring. Holman debated with Carol Mason, the anti-prehistoric-sugaring scholar through the 80s in many snippy articles.
This is a from a Menomini account circa 1921.
Trees were tapped by cutting them with an axe or a gouge and driving in a wooden sap spout on the sunny side of the tree. A tapper could do 200 to 300 trees per day. The sap was collected in birch bark dishes that were sealed with pine pitch. Great care was taken not to spill any sap or the ma''nabus would be offended and bring bad weather. The sap was collected in a hollowed out basswood log.
The syrup was refined using wood heat. A stick with a pine bough attached was used to skim the sap and prevent boiling over. When the sap starts to get stringy when lifted it's taken aside and strained of impurities and then cooked again over a small fire. After 15 to 30 minutes it is done. After this it is taken to a trough and pulverized into sugar. The sugar is graded according to color from white sugar to pena'o-omi (partridge dung).