An acre of sugar beets at 15-25 tons and 12-20% sugar holds 3,600-10,000 lb of sugar, so the sugar guide’s figure of 200-300 lb of raw sugar per acre implies a recovery of only 2-8%, only about a twelfth to a fiftieth of the sugar in the roots. At an assumed home recovery of 30-50% an acre gives roughly 1,080-5,000 lb, and the wood to boil it is the larger limit.
Sugar beet yield per acre is the weight of sugar recovered from one acre of roots, equal to root weight times sugar content times the fraction recovered by the process.
The Parent’s Figure Does Not Follow From Its Own Beets
The sugar guide states four things about beets: roots contain 12-20% sucrose by weight; a favourable yield is 15-25 tons of beets per acre; one acre gives roughly 200-300 lb of raw sugar; and that is enough to give a community of 100 about 2-3 lb of sugar per person a year. The third does not follow from the first two. This page derives the yield from the first two and shows what recovery the third implies.
Worked Example: Sugar In The Roots
Taking tons as short tons of 2,000 lb.
| Beet yield | 12% sugar | 15% sugar | 20% sugar |
|---|---|---|---|
| 15 tons (30,000 lb) | 3,600 lb | 4,500 lb | 6,000 lb |
| 20 tons (40,000 lb) | 4,800 lb | 6,000 lb | 8,000 lb |
| 25 tons (50,000 lb) | 6,000 lb | 7,500 lb | 10,000 lb |
The range is 3,600 lb (15 tons at 12%) to 10,000 lb (25 tons at 20%) of sucrose in the roots on one acre.
Worked Example: What Recovery Does 200-300 lb Imply?
- Highest case: 200 lb out of 10,000 lb is 2.0%. Lowest case: 300 lb out of 3,600 lb is 8.3%. In the middle row (6,000 lb) it is 200 ÷ 6,000 = 3.3% to 300 ÷ 6,000 = 5.0%.
- So the guide’s yield is 2-8% of the sugar in the roots. Industrial factories recover most of the sugar in the beets (recalled, well over 80%), and even a crude home process should recover far more than 2-8%.
- Scenarios at an assumed home recovery of 30% and 50% (no source; measure your own): 30% of 3,600 = 1,080 lb and 30% of 10,000 = 3,000 lb; 50% of 3,600 = 1,800 lb and 50% of 10,000 = 5,000 lb. So roughly 1,080-5,000 lb per acre.
- Against the guide’s 200-300 lb, the lowest scenario (1,080 lb) is 1,080 ÷ 300 = 3.6 times higher and the highest (5,000 lb) is 5,000 ÷ 200 = 25 times higher.
The guide’s own “2-3 lb per person for 100 people” is 200-300 lb. At 1,080-5,000 lb per acre, that need is met by 300 ÷ 1,080 = 0.28 acre down to 200 ÷ 5,000 = 0.04 acre. One acre could supply 11-50 lb of sugar per person per year for 100 people (1,080 ÷ 100 to 5,000 ÷ 100).
Energy And Land
- Sucrose is about 387 kcal per 100 g (recalled), or 1,755 kcal per lb. At 1,080-5,000 lb, an acre yields 1.9-8.8 million kcal of sugar, comparable with the caloric guide’s 1.2-5.25 million kcal for its staple crops. The sugar has no protein, fat or vitamins to speak of.
- What the land is no longer doing: an acre in beets is an acre not in potatoes (2.8-5.25 million kcal) or wheat (1.2-2.3 million) in the same plan. The beet tops and pulp go back to livestock.
- The wood: the extraction page works out about 177 MJ to evaporate the water from 100 lb of 15%-sugar beets with 90% extraction, which recovers 13.5 lb of sugar, so 177 ÷ 13.5 = 13.1 MJ per lb of sugar. At 14.5 MJ per kg for dry wood and pan efficiencies of 35% down to 15%, that is 13.1 ÷ (14.5 × 0.35) = 2.6 kg to 13.1 ÷ (14.5 × 0.15) = 6.0 kg of wood per lb of sugar. For the guide’s 200-300 lb a year, that is 200 × 2.6 = 520 kg up to 300 × 6.0 = 1,800 kg, about 0.5-1.8 tonnes, a small part of the 10.9-16.3 tonnes the kitchen burns in a year.
So a community can meet the guide’s modest sugar target from a fraction of an acre with modest fuel. What it cannot do is boil a whole acre’s crop at once without a very large supply of wood (Extraction by Boiling and Pressing).
What You Need
- A weighed sample of your own beets: root weight per plant, plants per acre, and sugar content if you can measure it
- Weights through the process: beets in, syrup or sugar out
- A record each season
Method: Derive Your Own Yield
Step 1: Weigh the roots from a measured plot and scale to an acre. Step 2: Take the sugar content from the guide’s 12-20% until you can measure it. Step 3: Weigh the syrup or sugar produced from a weighed batch of beets. Step 4: Compute recovery = sugar out ÷ sugar in the beets. Step 5: Size the plot from your sugar target and recovery, and size the wood from the fuel figures.
Common Mistakes
- Copying 200-300 lb per acre. It conflicts with the guide’s own beet figures.
- Sizing the plot from the crop, not the fuel. Wood sets the batch size.
- Counting syrup weight as sugar weight. A syrup of 66% sugar weighs about 1.5 times its sugar.
What’s Next
- Learn next: Maple Syrup Production — a sweetener that needs no crop land
- Combine with: Yield and Labor Requirements — the same comparison for sorghum