Short answer: the Keg accepts 37 crops. Measured by extra gold per machine per day, the best are Coffee Bean (1,000g), Starfruit (384g) and Ancient Fruit (282g). The list changes a lot if you have only a few machines, because a machine that is always busy earns more from a fast, valuable crop than a slow, cheap one.
How to read the table
"Extra gold per machine per day" is the price of the product minus what the crop would have sold for raw, spread over the days the machine takes, assuming it is never idle and the Artisan profession is on. It is the number to use when you own fewer machines than you have crops. If you have more machines than crops, rank by total gold instead, which is what the Keg vs Preserves Jar tool does with your real harvest. Times use 1,600 game minutes per day, as the wiki states.
| # | Crop | Makes | Price | Days | Extra gold per machine per day |
|---|---|---|---|---|---|
| 1 | Coffee Bean | Coffee (5 needed) | 150g | 0.08 | 1,000g |
| 2 | Starfruit | Wine | 3,150g | 6.25 | 384g |
| 3 | Ancient Fruit | Wine | 2,310g | 6.25 | 282g |
| 4 | Hops | Pale Ale | 420g | 1.41 | 281g |
| 5 | Wheat | Beer | 280g | 1.09 | 233g |
| 6 | Pumpkin | Juice | 1,008g | 3.75 | 183g |
| 7 | Pineapple | Wine | 1,260g | 6.25 | 154g |
| 8 | Red Cabbage | Juice | 819g | 3.75 | 149g |
| 9 | Melon | Wine | 1,050g | 6.25 | 128g |
| 10 | Rhubarb | Wine | 924g | 6.25 | 113g |
| 11 | Cauliflower | Juice | 550g | 3.75 | 100g |
| 12 | Artichoke | Juice | 504g | 3.75 | 92g |
| 13 | Yam | Juice | 504g | 3.75 | 92g |
| 14 | Amaranth | Juice | 471g | 3.75 | 86g |
| 15 | Kale | Juice | 345g | 3.75 | 63g |
| 16 | Strawberry | Wine | 504g | 6.25 | 61g |
| 17 | Beet | Juice | 315g | 3.75 | 57g |
| 18 | Taro Root | Juice | 315g | 3.75 | 57g |
| 19 | Radish | Juice | 282g | 3.75 | 51g |
| 20 | Bok Choy | Juice | 252g | 3.75 | 46g |
| 21 | Potato | Juice | 252g | 3.75 | 46g |
| 22 | Grape | Wine | 336g | 6.25 | 41g |
| 23 | Broccoli | Juice | 219g | 3.75 | 40g |
| 24 | Cactus Fruit | Wine | 315g | 6.25 | 38g |
| 25 | Cranberries | Wine | 315g | 6.25 | 38g |
| 26 | Eggplant | Juice | 189g | 3.75 | 34g |
| 27 | Garlic | Juice | 189g | 3.75 | 34g |
| 28 | Tomato | Juice | 189g | 3.75 | 34g |
| 29 | Powdermelon | Wine | 252g | 6.25 | 31g |
| 30 | Corn | Juice | 156g | 3.75 | 28g |
| 31 | Blueberry | Wine | 210g | 6.25 | 26g |
| 32 | Summer Squash | Juice | 141g | 3.75 | 26g |
| 33 | Green Bean | Juice | 126g | 3.75 | 23g |
| 34 | Carrot | Juice | 109g | 3.75 | 20g |
| 35 | Hot Pepper | Wine | 168g | 6.25 | 20g |
| 36 | Parsnip | Juice | 109g | 3.75 | 20g |
| 37 | Unmilled Rice | Juice | 93g | 3.75 | 17g |
Reading the top of the list
Coffee Beans come out first because Coffee takes only two hours per run and a Keg turns five beans into one. That is a real gain, but it isn't something you can scale: a single Coffee Bean plant doesn't give five beans a day, so a Keg usually waits for beans. Treat the top row as "good when you have the beans" and look further down for crops you grow in volume. Among fruit, Starfruit earns 384g a machine-day.
Each crop has its own page with profit per tile, fertilizer and the other machine. See also How many kegs do I need? for how many machines one plant keeps busy, and Best Greenhouse Setup for Money for the keg count that decides the greenhouse crop.